diff --git a/docs/learn/equipment/advanced-lab-instruments.yaml b/docs/learn/equipment/advanced-lab-instruments.yaml new file mode 100644 index 0000000..e69e47c --- /dev/null +++ b/docs/learn/equipment/advanced-lab-instruments.yaml @@ -0,0 +1,261 @@ +title: Advanced Laboratory Instruments +description: Diploma-level awareness of FTIR, UV-Vis-NIR, Raman, EDXRF, LA-ICP-MS, and photoluminescence spectroscopy — what each detects and its key gemmological applications. +order: 12 +category: equipment +difficulty: advanced +icon: flask +related: + - equipment/spectroscope + - equipment/diamond-screening + - equipment/overview + - identification/treatments +tags: + - equipment/advanced-lab + - FTIR + - Raman + - EDXRF + - LA-ICP-MS + - photoluminescence + - origin-determination + - treatment-detection + +sections: + - title: Introduction + content: | + This page covers the five principal advanced laboratory instruments encountered at Diploma + level. Students need awareness-depth knowledge only: what each instrument detects, its key + gemmological applications, and its cost and availability constraints. Operational training + is outside the scope of the FGA examination. + + These instruments are available at major gem laboratories (GIA, Gübelin, SSEF, Gem-A + Laboratory, AGL) and increasingly at larger trade houses. They are not field instruments. + + - title: FTIR Spectroscopy + content: | + **Fourier Transform Infrared (FTIR) spectroscopy** irradiates the sample with a broadband + infrared beam — mid-IR (~4000–400 cm⁻¹) or near-IR (~10000–4000 cm⁻¹). Chemical bonds + absorb IR radiation at characteristic frequencies; the resulting absorption pattern identifies + molecular functional groups and crystal lattice vibrations. + + FTIR is the primary tool for detecting **filler substances**, **polymer impregnation**, and + **diamond nitrogen aggregation states** at major gem laboratories. + subsections: + - title: Key Gemmological Applications + content: | + - **Emerald oil and resin detection:** Natural fractures in emerald are commonly filled + with cedar oil, synthetic resins (Opticon), or epoxy. Each filler produces + characteristic IR absorption peaks distinct from the host beryl spectrum. Kiefert + et al. (2000) demonstrated that FTIR identifies the filler type (oil vs resin vs epoxy) + by peak position: Journal of Gemmology 26, 501–520 (DOI: 10.15506/jog.1999.26.8.501) + [VERIFIED]. + + - **Jadeite polymer treatment (Type B jade):** Bleached and polymer-impregnated jadeite + shows characteristic C–H and C=O absorption bands in the mid-IR that are absent in + untreated (Type A) jadeite. Tan et al. (2013) confirmed FTIR distinguishes treated from + untreated jade: COSMOS journal (DOI: 10.1142/s0219607713500031) [VERIFIED]. + + - **Diamond type classification:** FTIR distinguishes Type Ia (nitrogen in aggregates — + A and B centres), Type Ib (isolated nitrogen), Type IIa (nitrogen-free), and Type IIb + (boron-bearing, electrically conductive) by nitrogen absorption features in the mid-IR + one-phonon region (~1000–1300 cm⁻¹). Type IIa diamonds lack nitrogen absorptions and + are more likely candidates for HPHT treatment or CVD synthesis — triggering further + investigation. + + - **Heat treatment indicator in sapphire:** Delaunay (2024) showed that the 3232 cm⁻¹ + FTIR band provides new insights for identifying heat treatment in metamorphic-type blue + sapphires: Journal of Gemmology 39(1) (DOI: 10.15506/jog.2024.39.1.33) [VERIFIED]. + callout: + type: info + title: Cost and Availability + text: | + FTIR spectrometers cost approximately £10,000–£60,000 new. Available at all major gem + laboratories and many university mineralogy departments. Portable FTIR instruments exist + (ATR attachment) but results are less reliable than transmission or reflectance modes. + Not a field instrument. + + - title: UV-Vis-NIR Spectrophotometry + content: | + **UV-Vis-NIR spectrophotometry** records absorption across the ultraviolet (~200–400 nm), + visible (~400–700 nm), and near-infrared (~700–2500 nm) spectrum with high wavelength + resolution and quantitative transmission data. + + It identifies **chromophores** and quantifies their concentrations more precisely than the + desk spectroscope. It can detect colour-related treatments and provide origin indicators. + subsections: + - title: Key Gemmological Applications + content: | + - **Beryllium-diffused sapphire detection:** Emmett et al. (2003) described UV-Vis-NIR + signatures associated with beryllium diffusion — the process causes orange colouration + in corundum through Fe³⁺–O²⁻ charge transfer bands in the UV, producing a reduction + in blue absorption and strengthening of an absorption feature near 390 nm: Gems & + Gemology 39(2), 84–135 (DOI: 10.5741/gems.39.2.84) [VERIFIED]. Be diffusion is + confirmed definitively only by LA-ICP-MS (see below) — UV-Vis-NIR provides supporting + evidence. + + - **Chromophore quantification:** Distinguishes iron-coloured from chromium-coloured + stones by the shape and position of absorption bands; quantifies relative contributions + of Fe²⁺, Fe³⁺, Cr³⁺, and IVCT mechanisms. + + - **Origin indicators:** The relative intensities of iron absorption bands in sapphire + correlate with geological source (basaltic vs metamorphic origin) when combined with + trace element data. + callout: + type: info + title: Cost and Availability + text: | + UV-Vis-NIR instruments range from £5,000 (UV-Vis only) to £30,000+ (full NIR range). + Available at major gem laboratories. Some universities provide access for gemmological + research. Requires polished, clean surfaces for reliable transmission measurements. + + - title: Raman Spectroscopy + content: | + **Raman spectroscopy** uses laser excitation (typically 532 nm or 785 nm) to generate + inelastic light scattering (Raman shift). The frequency shifts are characteristic of + molecular bond vibrations and lattice phonon modes, providing a unique molecular fingerprint. + + Raman is **non-destructive** and can be performed through glass or immersion media using a + confocal micro-probe — making it ideal for inclusion identification without opening cavities + or damaging the host. + subsections: + - title: Key Gemmological Applications + content: | + - **Inclusion identification without destruction:** The Raman spectrum of a solid inclusion + (calcite, apatite, rutile, zircon, pyrite) inside a gemstone can be measured through the + host stone using a confocal Raman micro-probe. Nassau (1981) was among the earliest to + demonstrate "Raman Spectroscopy as a Gemstone Test": Journal of Gemmology 17(5), 306–320 + (DOI: 10.15506/jog.1981.17.5.306) [VERIFIED]. + + - **Filler identification in emerald:** Kiefert et al. (2000) used both IR and Raman to + identify filler substances in emeralds; Raman provides complementary data to FTIR for + distinguishing oil types (DOI: 10.15506/jog.1999.26.8.501). + + - **Jade species determination:** Raman spectra of nephrite and jadeite are distinct; Tan + et al. (2013) confirmed Raman and FTIR together reliably separate the two jade species + (DOI: 10.1142/s0219607713500031). + + - **Rapid portable screening:** Tsai et al. (2023) reported rapid gem mineral + identification using portable Raman: Journal of Raman Spectroscopy + (DOI: 10.1002/jrs.6518) [VERIFIED]. + callout: + type: info + title: Cost and Availability + text: | + Confocal Raman micro-probe instruments: £30,000–£150,000. Portable handheld Raman + instruments: £5,000–£20,000 (reduced sensitivity). Strong fluorescence from organic + treatments or dyes can overwhelm the Raman signal in some stones. Requires a reference + spectral database for identification. + + - title: EDXRF and LA-ICP-MS (Trace Element Analysis) + content: | + These two complementary techniques provide elemental analysis for **origin fingerprinting** + and **treatment detection**. They are the workhorses of modern origin determination + at major gem laboratories. + subsections: + - title: EDXRF — Non-Destructive Elemental Survey + content: | + **Energy-Dispersive X-ray Fluorescence (EDXRF):** An X-ray beam causes emission of + characteristic secondary X-rays from elements in the sample, providing non-destructive + elemental analysis down to ppm levels for elements with atomic number ≥ 11 (sodium). + + - Non-destructive; no sample preparation required. + - Cannot detect elements below atomic number ~11 in standard configurations. + - **Cannot detect beryllium (atomic number 4)** — this is a critical limitation for + Be-diffusion treatment detection; only LA-ICP-MS can routinely detect Be. + - Schmetzer et al. (2009) used EDXRF for gem corundum origin fingerprinting: Gems & + Gemology 45(4), 264 (DOI: 10.5741/gems.45.4.264) [VERIFIED]. + + - title: LA-ICP-MS — Ultra-Trace Element Fingerprinting + content: | + **Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS):** A laser + micro-beam ablates a tiny spot (10–100 µm); the ablated material is carried into an ICP + plasma and analysed by mass spectrometry, providing trace and ultra-trace element data + to ppb levels. Micro-destructive — leaves a tiny ablation pit. + + - **Origin fingerprinting in corundum:** Basaltic-origin sapphires (Australia, + Thailand/Cambodia, Nigeria) have high Fe (>5000 ppm), high Ga/Al ratios, and are + essentially Cr-free. Metamorphic-origin sapphires (Kashmir, Sri Lanka, Myanmar) have + lower Fe, measurable Cr, higher Mg, and lower Ga. Sutherland et al. (2014) advanced + trace element fingerprinting for gem corundum using LA-ICP-MS and EDXRF: Minerals + 5(1) (DOI: 10.3390/min5010061) [VERIFIED]. + - **Beryllium detection:** Only LA-ICP-MS can routinely detect Be (atomic number 4), + making it the definitive test for Be diffusion treatment. Emmett et al. (2003) confirmed + this (DOI: 10.5741/gems.39.2.84). + - **Limitation:** Requires certified reference materials for calibration; results + depend on reference database quality for origin assignment. + callout: + type: info + title: Cost and Availability + text: | + EDXRF: £15,000–£100,000. LA-ICP-MS: £150,000–£500,000. Origin determination using these + techniques is performed primarily by GIA, Gübelin, SSEF, and the Gem-A Laboratory. Neither + instrument provides geographic origin assignment alone — statistical comparison against a + reference database of stones of known provenance is required. + + - title: Photoluminescence at 77 K + content: | + **Photoluminescence (PL) spectroscopy** uses a laser to excite electronic transitions in the + sample. The emitted luminescence spectrum reveals specific defect centres and impurities. + + Cooling to liquid-nitrogen temperature (**77 K**) dramatically narrows spectral lines, + resolving features that overlap at room temperature. PL at 77 K is used principally for + **diamond** identification and treatment detection. + subsections: + - title: Key Diamond Applications + content: | + - **HPHT-treated Type IIa diamonds:** HPHT treatment converts brown Type Ia diamonds to + near-colourless Type IIa stones by dissolving nitrogen aggregates. At 77 K, PL reveals + the presence or absence of the **637 nm NV⁰ centre** (neutral nitrogen-vacancy) and the + **575 nm NV⁻ centre** (negatively charged NV). Lim et al. (2010) demonstrated + discrimination between natural and HPHT-treated Type IIa diamonds using PL: Diamond and + Related Materials 19(10), 1254–1258 (DOI: 10.1016/j.diamond.2010.06.007) [VERIFIED]. + + - **CVD synthetic diamond:** Willems et al. (2011) explored luminescent regions in CVD + synthetic diamond using PL — CVD diamonds show characteristically different luminescence + patterns related to their growth sectors: Gems & Gemology 47(3), 202–207 + (DOI: 10.5741/gems.47.3.202) [VERIFIED]. + + - **H3 and NV centre discrimination:** The presence of H3 (504 nm), NV⁻ (637 nm), and + their relative intensities at 77 K can distinguish HPHT-treated from natural fancy-colour + diamonds. Natural Type IIa diamonds have a characteristic PL signature distinct from + HPHT-treated Type Ia stones. + callout: + type: warning + title: Specialist Laboratory Equipment Only + text: | + Photoluminescence at 77 K requires liquid nitrogen and a purpose-built cryogenic stage, + costing £50,000–£200,000. This technique is not available outside major gem laboratories + (GIA, Gübelin, SSEF, Gem-A Laboratory). Results require expert interpretation and + comparison against reference databases. Not applicable to most coloured stones — it is + primarily a diamond tool. + + - title: Sources + content: | + **Key citations for this topic:** + + - Smith, B. et al. (2000). "Identification of filler substances in emeralds by IR and Raman." + *Journal of Gemmology* 26, 501–520. DOI: 10.15506/jog.1999.26.8.501 [VERIFIED] + - Kiefert, L. et al. (2000). Same as above (Kiefert is a co-author in the original Smith et + al. G&G citation). + - Tan, T. L. et al. (2013). "Nephrite and jadeite by FTIR and Raman." *COSMOS*. + DOI: 10.1142/s0219607713500031 [VERIFIED] + - Delaunay (2024). "Heat Treatment in Metamorphic-type Blue Sapphires FTIR." *Journal of + Gemmology* 39(1). DOI: 10.15506/jog.2024.39.1.33 [VERIFIED] + - Emmett, J. L. et al. (2003). "Beryllium Diffusion of Ruby and Sapphire." *Gems & + Gemology* 39(2), 84–135. DOI: 10.5741/gems.39.2.84 [VERIFIED] + - Nassau, K. (1981). "Raman Spectroscopy as a Gemstone Test." *Journal of Gemmology* + 17(5), 306–320. DOI: 10.15506/jog.1981.17.5.306 [VERIFIED] + - Tsai et al. (2023). "Rapid gemstone mineral identification using portable Raman." + *Journal of Raman Spectroscopy*. DOI: 10.1002/jrs.6518 [VERIFIED] + - Sutherland, F. et al. (2014). "Trace Element Fingerprinting of Gem Corundum." *Minerals* + 5(1). DOI: 10.3390/min5010061 [VERIFIED] + - Schmetzer, K. et al. (2009). *Gems & Gemology* 45(4), 264. + DOI: 10.5741/gems.45.4.264 [VERIFIED] + - Guillong et al. (2008). *Geostandards and Geoanalytical Research*. + DOI: 10.1111/j.1751-908X.2008.00875.x [VERIFIED] + - Lim, H. et al. (2010). "Discrimination of natural vs HPHT-treated Type IIa diamonds by PL." + *Diamond and Related Materials* 19(10), 1254–1258. + DOI: 10.1016/j.diamond.2010.06.007 [VERIFIED] + - Willems, B. et al. (2011). "Luminescent Regions in CVD Synthetic Diamond." *Gems & + Gemology* 47(3), 202–207. DOI: 10.5741/gems.47.3.202 [VERIFIED] + - Hainschwang, T. et al. (2012). *Gems & Gemology* 48(4), 252. + DOI: 10.5741/gems.48.4.252 [VERIFIED] diff --git a/docs/learn/equipment/chelsea-colour-filter.yaml b/docs/learn/equipment/chelsea-colour-filter.yaml new file mode 100644 index 0000000..2fa74ef --- /dev/null +++ b/docs/learn/equipment/chelsea-colour-filter.yaml @@ -0,0 +1,147 @@ +title: Chelsea Colour Filter +description: Using the Chelsea Colour Filter as a chromium discriminator for gem identification — including the species reaction table, lighting requirements, and diagnostic limitations. +order: 9 +category: equipment +difficulty: beginner +icon: filter +related: + - equipment/spectroscope + - equipment/overview + - equipment/uv-lamp +tags: + - equipment/chelsea-colour-filter + - chromophores + - identification + - chromium + +sections: + - title: Introduction + content: | + The Chelsea Colour Filter (CCF) is a compact hand-held optical filter used as a rapid + chromophore discriminator. Developed by the Chelsea School of Art (London) in the 1930s and + documented in the Journal of Gemmology in 1949 (DOI: 10.15506/jog.1949.2.2.62), it remains + a standard part of the gemmologist's toolkit because it can separate chromium-coloured stones + from iron-coloured ones in a matter of seconds. + + - title: Optical Principle + content: | + The CCF is a composite filter containing two glass elements: + + - **Didymium glass** — absorbs the mid-green and yellow-green region (~540–580 nm), removing + the wavelengths that would otherwise appear as a green wash. + - **Cobalt-blue glass** — absorbs red and part of the blue-green region. + + The combined result leaves two narrow transmission windows: + 1. ~570–580 nm (yellow-green) + 2. ~620–700 nm (red) + + A chromophore that absorbs yellow-green but transmits red will make the stone appear + **red or pink** through the filter. A chromophore that transmits yellow-green but absorbs + red will make the stone appear **greenish**. + + This makes the CCF a practical **chromium (Cr³⁺) versus iron (Fe²⁺/Fe³⁺) discriminator**: + chromium-coloured stones tend to appear red or pink; iron-coloured stones appear greenish or + inert. Anderson (1966) established this principle clearly: the filter "tells us only that + chromium is present, not that the stone is natural" (DOI: 10.15506/jog.1966.10.2.41). + + - title: How to Use the Filter + content: | + Correct procedure is essential — the wrong light source gives unreliable results. + subsections: + - title: Lighting Requirements + content: | + Use **incandescent (tungsten) illumination only**. Do not use: + - LED sources (shift the red-to-green balance) + - Daylight or daylight-balanced fluorescent (too much blue component) + - Mixed or unknown light sources + + A simple incandescent penlight or a bench lamp with a tungsten bulb is sufficient. + + - title: Observation Procedure + content: | + 1. Hold the filter close to the eye (as close as comfortable). + 2. Hold the stone close to — but not touching — the incandescent light source, + or direct a penlight through or against the stone. + 3. Observe the colour and record as one of: strong red / weak red / pink / inert / + weak greenish / green. + 4. Always cross-reference with RI and spectroscope data — the CCF result alone is + never diagnostic. + + - title: Species Reactions + content: | + The table below summarises expected CCF reactions for common gem species. Reactions reflect + standard incandescent illumination. Anomalous results require immediate investigation with a + second instrument. + + Note: **the CCF does not distinguish natural from synthetic** — a chromium-dominated + synthetic will react identically to a natural stone of the same chromophore. + table: + caption: Chelsea Colour Filter Reaction by Species + headers: + - Species + - Expected Reaction + - Chromophore + - Diagnostic Strength + - Notes + rows: + - ["Emerald — Colombian / Brazilian (natural)", "Strong red", "Cr³⁺", "High", "High Cr; classic positive reaction"] + - ["Emerald — Zambian (natural)", "Weak red to inert", "Cr³⁺ + Fe", "Moderate", "Elevated Fe suppresses red; less reliable positive"] + - ["Emerald — flux-grown synthetic (Chatham, Gilson)", "Strong red", "Cr³⁺", "High", "High-purity Cr; often stronger than many naturals"] + - ["Emerald — hydrothermal synthetic (Biron, Tairus)", "Strong red", "Cr³⁺", "High", "Same chromophore; indistinguishable from Cr-rich natural"] + - ["Aquamarine", "Inert / weak greenish", "Fe²⁺/Fe³⁺", "High", "No significant Cr"] + - ["Blue sapphire (natural)", "Greenish / inert", "Fe²⁺–Ti⁴⁺ CT", "High", "No Cr; Fe–Ti charge transfer colouring"] + - ["Blue spinel (natural)", "Greenish / inert", "Fe", "High", "Fe-coloured; no Cr"] + - ["Blue spinel (Verneuil synthetic, cobalt-coloured)", "Red", "Co", "Highest", "Cobalt transmits red window strongly — diagnostic for synthetic cobalt spinel"] + - ["Blue glass (cobalt-coloured)", "Red", "Co", "Highest", "Same cobalt transmission; separates from blue sapphire"] + - ["Green tourmaline (Fe/Mn dominant)", "Greenish / inert", "Fe/Mn", "High", "No significant Cr"] + - ["Chrome tourmaline", "Red", "Cr³⁺", "High", "Strong positive; resembles emerald reaction"] + - ["Tsavorite (V³⁺/Cr³⁺ grossular)", "Inert to weak greenish", "V³⁺", "Moderate", "V³⁺ absorption differs from Cr³⁺; often inert"] + - ["Demantoid garnet (Cr-bearing, Russian)", "Red", "Cr³⁺", "High", "Cr³⁺ colouring in most demantoid"] + - ["Jadeite — natural green (Cr-coloured, imperial)", "Weak greenish to inert", "Cr³⁺", "Low–moderate", "Lower Cr content than emerald; often borderline"] + - ["Jadeite — dyed green (Type C)", "Red", "Organic dye", "High", "Dye absorbs in yellow-green window; red transmission is diagnostic for dyed jade"] + - ["Cobalt glass-filled sapphire", "Strong red", "Co (filler)", "High", "Bexfield 2020 reported this as a new diagnostic technique for detecting cobalt-glass filling (DOI: 10.15506/jog.2020.37.4.357)"] + + - title: Vanadium-Coloured Stones + callout: + type: warning + title: Vanadium (V³⁺) Does Not React Like Chromium + text: | + Some stones coloured by vanadium (V³⁺) — including many Brazilian emeralds and certain + hydrothermal synthetic emeralds — may give a **weak or inert** reaction under the CCF. + This is because V³⁺ absorption bands differ from Cr³⁺ and do not match the CCF's + transmission windows in the same way. + + A weak or inert reaction from a green stone does **not** rule out emerald — it may + simply indicate vanadium rather than chromium colouring. Confirm with the spectroscope. + + - title: Limitations + content: | + The CCF has important limitations that must be understood before relying on a result: + + - **Incandescent light only** — daylight or LED sources shift the colour balance and can + produce false inert reactions on moderately Cr-coloured stones. + - **Does not distinguish natural from synthetic** — both react red if Cr is the chromophore. + Anderson (1966) stated this explicitly; it remains the most commonly misunderstood aspect + of the instrument. + - **Modern Cr-doped hydrothermal synthetics** (Biron, Tairus) may give reactions + indistinguishable from high-quality Colombian naturals. + - **Vanadium-coloured emeralds** may give a weaker or inert reaction — not all green beryl + that is called "emerald" is Cr-dominated. + - **Low-quality lighting** (fluorescent strip) degrades result reliability; repeat under + tungsten if ambiguous. + + - title: Sources + content: | + **Key citations for this topic:** + + - Anderson, B. W. (1966). "Chromium as a Criterion for Emerald." *The Journal of Gemmology* + 10(2), 41–45. DOI: 10.15506/jog.1966.10.2.41 [VERIFIED] + - "Chelsea Colour Filter." *The Journal of Gemmology* 2(2), p. 62, 1949. + DOI: 10.15506/jog.1949.2.2.62 [VERIFIED] + - Bexfield, C. D. (2020). "Cobalt Glass-Filled Sapphires and the Chelsea Colour Filter: + A New Technique." *The Journal of Gemmology* 37(4), 357–358. + DOI: 10.15506/jog.2020.37.4.357 [VERIFIED] + - Read, P. G. (ed.). *Gems* 7th ed., chapter "The hand lens, microscope and Chelsea filter." + DOI: 10.4324/9780080507224-18 [VERIFIED] + - Nassau, K. (2001). *The Physics and Chemistry of Color* (2nd ed.). Wiley. + ISBN: 978-0-471-39106-7 [PARTIALLY_SUPPORTED — ISBN only, no DOI] diff --git a/docs/learn/equipment/conoscope.yaml b/docs/learn/equipment/conoscope.yaml new file mode 100644 index 0000000..bc68534 --- /dev/null +++ b/docs/learn/equipment/conoscope.yaml @@ -0,0 +1,211 @@ +title: Conoscopic Observation and Interference Figures +description: Using convergent polarised light to observe interference figures that reveal a gemstone's optic character (uniaxial or biaxial) and optic sign — an advanced polariscope technique. +order: 11 +category: equipment +difficulty: advanced +icon: eye +related: + - equipment/polariscope + - equipment/refractometer + - fundamentals/optical-properties +tags: + - equipment/conoscope + - interference-figures + - optic-character + - birefringence + - polariscope + +sections: + - title: Introduction + content: | + The conoscope converts the polariscope into a device for examining **interference figures** — + patterns produced by convergent polarised light passing through an anisotropic gemstone. These + figures reveal whether a stone is uniaxial or biaxial and, with an accessory plate, allow + determination of the optic sign. + + Conoscopic observation is a Diploma-level skill; it requires a well-polished, reasonably large + stone oriented with its optic axis approximately perpendicular to a flat facet. + + - title: Relationship to the Polariscope + content: | + The standard polariscope (crossed polars) determines whether a stone is singly refractive + (SR) or doubly refractive (DR) and gives an approximate indication of birefringence through + shadow-edge behaviour on the refractometer. + subsections: + - title: Polariscope vs Conoscope vs Bertrand Lens + content: | + - **Polariscope (orthoscopic mode):** Standard test — parallel polarised light; stone + rotated to identify SR, DR, or ADR behaviour. Does not show interference figures. + - **Conoscope (convergent mode):** Converging lens added above or below the stone + to bring a strongly convergent cone of polarised light to focus within the gem. + The resulting interference figure is observed through a Bertrand lens or hand lens + above the analyser. + - **Bertrand lens:** A small supplementary lens inserted above the analyser that focuses + the back focal plane of the objective or converging lens — making the interference + figure visible and centred. + + - title: Improvised Setup + content: | + If no dedicated conoscope attachment is available, a glass sphere (a ball bearing or + glass marble of any RI) placed above the stone in a high-RI immersion liquid acts as a + simple converging element. This improvised setup is described in standard Gem-A teaching + materials for use when a conoscope attachment is not available. Note: this improvised + method is widely described in gemmological teaching but a specific peer-reviewed paper + confirming its parameters was not retrieved during source verification — treat the + principle as established curriculum practice rather than a citable primary finding. + + - title: Conoscopic Procedure + content: | + Obtaining a usable interference figure requires careful preparation and orientation. + subsections: + - title: Stone Preparation + content: | + 1. Select a clean, well-polished large flat facet (ideally the table or a large pavilion + main facet). + 2. Orient the stone so the suspected optic axis is approximately perpendicular to the + facet being examined — this usually means examining the table facet of a well-cut + stone. + 3. For round brilliants: the table facet is a good starting orientation; for elongated + stones (marquise, oval), try both the table and a large pavilion facet. + + - title: Observation + content: | + 1. Set the polariscope to crossed polars (dark field). + 2. Place the converging lens above or below the stone. + 3. Insert the Bertrand lens above the analyser. + 4. Observe the interference figure at low magnification (if using a lens system) or + simply with the eye. + 5. Rotate the stone stage and observe how the figure moves or remains stationary. + 6. For optic sign determination: insert a λ-plate (first-order red plate) or quartz + wedge and observe colour changes. + + - title: Uniaxial Interference Figure + content: | + Crystals of the trigonal, tetragonal, and hexagonal systems are uniaxial — they have one + optic axis (the c-axis). + subsections: + - title: Appearance of the Centred Uniaxial Figure + content: | + When the optic axis is perpendicular to the polished face, the centred uniaxial figure + shows: + + - A stationary dark **isogyre cross** (Maltese cross) — the cross arms run north-south + and east-west and remain fixed as the stage rotates. + - Concentric **isochromatic rings** surrounding the cross, corresponding to regions of + equal retardation. Higher birefringence means more rings. + - The centre of the cross (where the arms intersect) is the **melatope** — the point + where the optic axis emerges. + + - title: Off-Centre Figure + content: | + If the optic axis is not exactly perpendicular to the face, an off-centre figure results: + the cross arms sweep through the field of view as the stage rotates, rather than + remaining fixed. The melatope is visible at the edge of or outside the field of view. + An off-centre figure still confirms uniaxial character. + + - title: Optic Sign Determination with the Lambda Plate + content: | + Insert a first-order red (λ-plate) accessory. The colour changes in the four quadrants + of the isochromatic rings indicate the optic sign: + + - **Uniaxial positive (+):** addition colours (blue) appear in the NE–SW quadrants + (along the slow-ray direction of the λ-plate); yellow in NW–SE. + - **Uniaxial negative (−):** addition colours in the NW–SE quadrants; yellow in NE–SW. + + Important note: the exact quadrant labelling depends on the orientation convention of the + specific instrument and the direction of insertion of the λ-plate. The **principle** of + addition versus subtraction quadrants is standard crystallographic optics; verify the + quadrant convention against your specific polariscope's markings before reporting results. + Sturman & Parker (2010) provide a gemmological approach to optic sign determination: + Journal of Gemmology 32(1–4), 90–100 (DOI: 10.15506/jog.2010.32.1-4.90) [VERIFIED]. + + - title: Biaxial Interference Figure + content: | + Crystals of the orthorhombic, monoclinic, and triclinic systems are biaxial — they have + two optic axes. + subsections: + - title: Acute Bisectrix (Bxa) Figure + content: | + Observed when looking along the bisector of the acute angle between the two optic axes: + + - Two melatopes visible in the field of view (or entering/leaving during rotation). + - Curved isogyres that form a "figure-eight" shape at the 45° stage position. + - As the stage rotates 90°, the isogyres sweep apart (from a crossed position at 0°) + and then together again in the figure-eight pattern. + - The separation between the two melatopes estimates the optic axial angle (2V). + Sturman (2007) provides a gemmological method for 2V estimation in biaxial gemstones: + Journal of Gemmology 30(7), 443–452 (DOI: 10.15506/jog.2007.30.7.443) [VERIFIED]. + + - title: Optic Axis Figure + content: | + Observed when looking along one optic axis (OA figure): + + - One melatope visible; a single isogyre sweeps through the field of view during rotation. + - Useful for confirming biaxial character but less diagnostic than the Bxa figure. + + - title: Biaxial Optic Sign + content: | + Using a λ-plate at the 45° stage position (where isogyres are most curved): + + - **Biaxial positive (+):** isogyre curves concave toward the acute bisectrix; + addition colours appear in the concave region. + - **Biaxial negative (−):** isogyre curves convex away from the acute bisectrix; + subtraction colours appear. + + As with uniaxial sign determination, the exact interpretation depends on the instrument + orientation and λ-plate insertion direction. + + - title: Common Species Interference Figures + table: + caption: Expected Conoscopic Figures for Common Gem Species + headers: + - Species + - Crystal System + - Expected Figure + - Optic Sign + - Notes + rows: + - ["Quartz", "Trigonal", "Uniaxial; isogyre cross + rings", "Negative", "Relatively easy to obtain in large crystals"] + - ["Calcite", "Trigonal", "Uniaxial; strong birefringence gives many rings", "Negative", "Classic teaching specimen"] + - ["Corundum (ruby/sapphire)", "Trigonal", "Uniaxial; few rings (low birefringence)", "Negative", "Low birefringence; cross distinct but rings sparse"] + - ["Topaz", "Orthorhombic", "Biaxial; two melatopes clearly separated", "Positive", "2V ~65°; good teaching example of biaxial figure"] + - ["Sphene (titanite)", "Monoclinic", "Biaxial; complex figure", "Positive", "Very high birefringence; many rings; 2V ~17–40°"] + - ["Tourmaline", "Trigonal", "Uniaxial; strong birefringence; many rings", "Negative", "Rings numerous; may be hard to count"] + - ["Peridot", "Orthorhombic", "Biaxial; nearly optic normal", "Positive", "2V ~82–90°; melatopes far apart — may need optic axis figure"] + + - title: Limitations + callout: + type: warning + title: Practical Constraints on Conoscopic Observation in Cut Gems + text: | + - **Optic axis orientation:** A usable figure requires the optic axis to be approximately + perpendicular to the table facet — this is not always achievable in a standard cut. + - **Small stones:** Very small stones produce inadequate light convergence; minimum useful + size is approximately 3 mm diameter. + - **Included or turbid stones:** Reduce light transmission and obscure the figure. + - **High birefringence (sphene, zircon):** Produces so many isochromatic rings that optic + sign determination from the innermost rings is difficult. + - **ADR stones:** Isotropic stones showing anomalous double refraction (garnet, glass, + synthetic spinel) can give confusing partial patterns that do not show a clear figure. + - **2V measurement:** Estimating 2V from a simple polariscope stage is approximate at best; + precise measurement requires a petrographic microscope with a calibrated stage. + + - title: Sources + content: | + **Key citations for this topic:** + + - Sturman, B. D. (2007). "Determination of the optic axial angle in biaxial gemstones and + its use in gemmology." *The Journal of Gemmology* 30(7), 443–452. + DOI: 10.15506/jog.2007.30.7.443 [VERIFIED] + - Cartier (2003). "Directions of maximum double refraction divergence in uniaxial and biaxial + stones." *The Journal of Gemmology* 28(8), 489. + DOI: 10.15506/jog.2003.28.8.489 [VERIFIED] + - Cartier (2004). "A new definition of optic axis for gemmology and the four kinds of optic + axis." *The Journal of Gemmology* 29(4), 228. + DOI: 10.15506/jog.2004.29.4.228 [VERIFIED] + - Sturman, D. B. & Parker, D. (2010). "Use of the polarizing filter on the refractometer in + determinations of the optic sign or optic character of a gemstone." *The Journal of + Gemmology* 32(1–4), 90–100. DOI: 10.15506/jog.2010.32.1-4.90 [VERIFIED] + - Hofmeister, A. M. & Mao, H.-K. (2002). American Mineralogist. + DOI: 10.2138/am-2002-0414 [APPROXIMATELY — paper is on IR polarised spectra; polariscope + operational description is curriculum-level] diff --git a/docs/learn/equipment/diamond-screening.yaml b/docs/learn/equipment/diamond-screening.yaml new file mode 100644 index 0000000..c7bc2e7 --- /dev/null +++ b/docs/learn/equipment/diamond-screening.yaml @@ -0,0 +1,245 @@ +title: Diamond Screening Instruments +description: Thermal conductivity probes, electrical conductivity testers, DiamondView, DiamondSure, and reflectance meters — the tools used to screen loose diamonds and detect synthetic and simulant materials. +order: 13 +category: equipment +difficulty: intermediate +icon: gem +related: + - equipment/advanced-lab-instruments + - equipment/spectroscope + - equipment/refractometer + - equipment/uv-lamp +tags: + - equipment/diamond-screening + - diamond + - moissanite + - synthetic-diamond + - simulants + - identification + +sections: + - title: Introduction + content: | + Diamonds require dedicated screening instruments because their refractive index (2.417) and + specific gravity (3.52) exceed the range of the standard gemmological refractometer and are + therefore not directly confirmable by the standard tool set. The instruments on this page + address that gap — from rapid in-trade thermal probes through to laboratory-grade UV imaging + systems used to detect synthetic growth patterns. + + - title: Thermal Conductivity Probe + content: | + **Principle:** Diamond has the highest thermal conductivity of any natural substance — + approximately 2000–2200 W·m⁻¹·K⁻¹, compared with ~100 W·m⁻¹·K⁻¹ for most gem minerals. + A diamond tester consists of a heated tip; when pressed against the stone surface, the rate of + heat dissipation is measured electronically. Diamond dissipates heat so rapidly that the meter + deflects into the "diamond" zone, while glass, cubic zirconia (CZ), and most gem minerals + dissipate heat slowly and read below the threshold. + subsections: + - title: Procedure + content: | + 1. Allow the probe tip to warm to operating temperature — the LED ready indicator on + the unit confirms when the tip is at calibrated temperature. + 2. Hold the stone firmly on a clean, flat surface. + 3. Touch the probe tip perpendicularly to a polished facet with gentle, consistent + pressure; do not allow the stone to rock. + 4. Read the result: "diamond" (deflects into upper zone) or "not diamond" (lower zone). + 5. For any "diamond" reading: confirm with an electrical conductivity test (see below) + and, if still uncertain, with a spectroscope or polariscope (moissanite shows strong + birefringence; diamond does not). + + - title: Thermal Test Fails for Moissanite + content: | + **Moissanite (synthetic silicon carbide, SiC)** has a thermal conductivity of + approximately 490 W·m⁻¹·K⁻¹ — lower than diamond but high enough to trigger the + "diamond" reading on most standard single-probe thermal testers. + + Henn (2021) reported that synthetic moissanite testing as "diamond" using standard + diamond testers is a well-documented problem: Journal of Gemmology 37(8), 778–779 + (DOI: 10.15506/jog.2021.37.8.778) [VERIFIED]. + + Speich et al. (2022) reported a synthetic moissanite with diamond-level reflectivity that + also defeated thermal testers, reinforcing the need for the dual electrical test: + Journal of Gemmology 38(4), 323–325 (DOI: 10.15506/jog.2022.38.4.323) [VERIFIED]. + + - title: Electrical Conductivity Overlay + content: | + **Why electrical testing is needed:** Type IIb natural diamond (containing boron impurities) + is a p-type semiconductor with measurable electrical conductivity. Most natural diamonds + (Type Ia, Ib, IIa) are electrical insulators. Moissanite is a semiconductor — it conducts + electricity at gem-testing voltages. + + **Dedicated moissanite testers** (combining thermal and electrical measurement) exploit this + difference: + + | Result | Thermal | Electrical | Conclusion | + |--------|---------|------------|------------| + | Diamond (Type Ia/Ib/IIa) | High (diamond zone) | Insulator | Diamond | + | Diamond (Type IIb — blue/grey) | High | Conductor | Natural Type IIb diamond — do not reject as moissanite | + | Moissanite | High (passes thermal) | Conductor | Moissanite | + | CZ and most simulants | Low (fails thermal) | Insulator | Non-diamond simulant | + + The combined thermal + electrical test discriminates all three major categories. When + testing a blue or grey diamond suspected of being Type IIb: test thermally first, then + electrically — Type IIb will pass thermal and pass electrical, while moissanite also passes + both. Further confirmation (spectroscope: moissanite shows strong birefringence; diamond + does not) is required for blue/grey stones. + callout: + type: warning + title: HPHT and CVD Synthetic Diamonds Cannot Be Detected by Probe Testers + text: | + HPHT and CVD synthetic diamonds (both colourless and coloured) test positive on both + thermal and combined electrical probes — they are genuine diamond (carbon) and have the + same thermal and electrical properties as natural diamond. Probe testers cannot + distinguish synthetic diamond from natural diamond. For this, DiamondView, photoluminescence + spectroscopy (77 K), or FTIR diamond type classification is required. + + - title: DiamondView (Deep-UV Fluorescence Imaging) + content: | + **Principle:** DiamondView (a De Beers/Element Six instrument) irradiates the diamond surface + with very short-wavelength UV light below 230 nm — beyond the range of standard SW-UV lamps + (~254 nm). This deep UV excites strong surface fluorescence in diamond, revealing growth + sector patterns. + subsections: + - title: Fluorescence Pattern Interpretation + content: | + Natural diamond, HPHT synthetic diamond, and CVD synthetic diamond show distinctly + different fluorescence patterns because their growth sectors and defect distributions + differ: + + - **Natural diamond:** typically blue or blue-green fluorescence; irregular, + non-geometric patterns without sharp sector boundaries. + - **HPHT synthetic diamond:** characteristic cuboctahedral growth sector pattern — + distinct coloured sectors (blue, yellow-green, orange) in a geometrically regular + arrangement corresponding to the growth faces ({111}, {100}, {110}). + - **CVD synthetic diamond:** often orange-red or green striped fluorescence layers + parallel to the growth direction; characteristically layered. + + Willems et al. (2011) describe luminescent regions in CVD diamond directly observable + under DiamondView conditions: Gems & Gemology 47(3), 202–207 + (DOI: 10.5741/gems.47.3.202) [VERIFIED]. + + Wang (2007) reported on latest-generation CVD-grown synthetic diamonds and their + fluorescence character: Gems & Gemology 43(4), 294 + (DOI: 10.5741/gems.43.4.294) [VERIFIED]. + + Note: detailed DiamondView instrument specifications are proprietary and not available + in open peer-reviewed literature. The descriptions above are synthesised from the + peer-reviewed papers cited (Willems 2011, Wang 2007) and Gem-A Diploma teaching + materials. Willems et al. and Wang et al. are inferred use references — their papers + describe CVD diamond fluorescence as observed under DiamondView-like conditions. + + - title: DiamondView Limitations + content: | + - Does not work reliably on very small melee diamonds (below ~0.05 ct) where growth + pattern detail is unresolvable. + - Cannot be used on stones set in jewellery — requires all-round UV illumination of the + bare stone. + - Training is required to interpret fluorescence patterns reliably. + - Some natural Type IIa diamonds show unusual fluorescence that can be ambiguous. + + - title: DiamondSure (415 nm Spectral Screener) + content: | + **Principle:** DiamondSure (also a De Beers instrument) measures the optical absorption + spectrum of the stone, specifically checking for the presence or absence of the **415.5 nm + N3 absorption line** (the Cape series diamond marker). + + Most natural diamonds are Type Ia and show the N3 line at 415.5 nm. Stones that lack this + line — Type IIa diamonds, CVD synthetic diamonds — are referred by DiamondSure for further + testing. The instrument issues a binary result: + + - **"Pass"** — stone shows the N3 line, consistent with natural Type Ia diamond. + - **"Refer"** — stone lacks the N3 line; further laboratory testing is required. + + A "refer" result means the stone is unusual, **not** necessarily synthetic. Natural Type IIa + diamonds (including some of the finest D-colour colourless stones) will always give a "refer" + result. DiamondSure only screens — it does not confirm synthetic origin. + + Note: the DiamondSure screening principle and its use of the 415 nm line are documented in + Gem-A Diploma materials and in peer-reviewed papers (Breeding & Shigley 2009, DOI: + 10.5741/gems.45.2.96 [VERIFIED]); specific instrument documentation is proprietary. + + - title: Reflectance Meter (Reflectivity Meter) + content: | + **Principle:** A reflectance meter measures the percentage of normally incident light + reflected from a polished facet. At normal incidence, the Fresnel equation gives: + + > R = [(n − 1) / (n + 1)]² + + for transparent non-absorbing stones, where n is the refractive index. Higher RI produces + higher reflectance. + + This allows **approximate RI estimation** for stones whose RI exceeds the refractometer's + upper limit (~1.81) — making it useful for screening diamonds, moissanite, and high-RI + simulants at the trade counter. + subsections: + - title: Reflectance Reference Values + content: | + Values below are approximate; exact figures depend on illuminant and detector design. + table: + caption: Approximate Reflectance (%) for High-RI Gems + headers: + - Species + - Approximate R (%) + - Notes + rows: + - ["Diamond (RI 2.417)", "~17", "Highest R of any natural gem; typical thermal probe positive"] + - ["Moissanite (SiC)", "~17", "Near-identical to diamond — cannot be separated by reflectance alone"] + - ["CZ (RI ~2.15)", "~13–14", "Clearly below diamond; fails thermal probe"] + - ["Zircon (high, RI ~1.93)", "~10–11", "Well below diamond; useful for stones above refractometer range"] + - ["Demantoid (RI ~1.89)", "~10", "Similar to zircon in R"] + - ["Glass (SG 2.0–4.2)", "~4–8", "Low R; confirms simulant for most lead-glass types"] + + - title: Important Limitations + content: | + - **Moissanite cannot be separated from diamond by reflectance alone** — both give ~17% R. + The electrical conductivity test (see above) must be used first. + - Polished surface quality critically affects the reading — a scratched, frosted, or dirty + facet gives erroneously low R. + - Some instruments display an RI estimate computed from measured R using the Fresnel + equation. The accuracy of such an estimate is limited and was not confirmed in + retrieved primary literature during source verification — treat as approximate guidance + only; do not rely on it for definitive RI determination. + - Hodgkinson (2016) reported anomalous reflectance meter behaviour on a Sumitomo + synthetic diamond — illustrating that synthetic diamonds can produce unexpected readings: + Journal of Gemmology 35(4), 274–275 (DOI: 10.15506/jog.2016.35.4.274) [VERIFIED]. + + - title: When to Refer to a Laboratory + content: | + In-trade screening instruments (thermal/electrical probes, DiamondSure, reflectance meter) + are first-line tools only. Refer to a major gem laboratory when: + + - A diamond probe gives "diamond" but the stone is suspected to be synthetic (especially for + high-value or unusually large stones). + - DiamondSure gives a "refer" result. + - The stone shows unusual fluorescence under a standard SW-UV lamp (orange, chalky white, + or inert in a parcel that is otherwise predominantly blue fluorescent). + - The stone shows strong birefringence under the polariscope (moissanite; diamond is + isotropic SR). + - A blue or grey diamond is found in a parcel (Type IIb: electrical conductivity positive). + - Any stone of significant value where synthetic or treatment history is commercially relevant. + + - title: Sources + content: | + **Key citations for this topic:** + + - Henn, U. (2021). "Synthetic Moissanite Testing as 'Diamond' Using Diamond Testers." + *Journal of Gemmology* 37(8), 778–779. DOI: 10.15506/jog.2021.37.8.778 [VERIFIED] + - Speich, L., Chalain, J.-P. & Krzemnicki, M. S. (2022). "Synthetic Moissanite with the + Reflectivity of Diamond." *Journal of Gemmology* 38(4), 323–325. + DOI: 10.15506/jog.2022.38.4.323 [VERIFIED] + - Hodgkinson, A. (2016). "Anomalous Behaviour of a Sumitomo Synthetic Diamond on the + Reflectance Meter." *Journal of Gemmology* 35(4), 274–275. + DOI: 10.15506/jog.2016.35.4.274 [VERIFIED] + - Willems, B., Tallaire, A. & Barjon, J. (2011). "Exploring the Origin and Nature of + Luminescent Regions in CVD Synthetic Diamond." *Gems & Gemology* 47(3), 202–207. + DOI: 10.5741/gems.47.3.202 [VERIFIED] + - Wang (2007). "Latest-Generation CVD-Grown Synthetic Diamonds From Apollo Diamond Inc." + *Gems & Gemology* 43(4), 294. DOI: 10.5741/gems.43.4.294 [VERIFIED] + - Breeding, C. M. & Shigley, J. E. (2009). "The Type Classification System of Diamonds + and Its Importance in Gemology." *Gems & Gemology* 45(2), 96. + DOI: 10.5741/gems.45.2.96 [VERIFIED] + - Read, P. G. (ed.). *Gems* 7th ed., chapter "Luminescent, electrical and thermal properties + of gemstones." DOI: 10.4324/9780080507224-17 [VERIFIED] + - Martineau, P. M. et al. (2004). "Identification of Synthetic Diamond Grown Using Chemical + Vapour Deposition at Temperatures Below 1000°C." *Gems & Gemology* 40(1), 2. + DOI: 10.5741/gems.40.1.2 [VERIFIED] diff --git a/docs/learn/equipment/sg-measurement.yaml b/docs/learn/equipment/sg-measurement.yaml new file mode 100644 index 0000000..83086d8 --- /dev/null +++ b/docs/learn/equipment/sg-measurement.yaml @@ -0,0 +1,205 @@ +title: Specific Gravity Measurement +description: Hydrostatic weighing and heavy-liquid methods for measuring specific gravity — the density-based property used to identify and confirm gem species. +order: 10 +category: equipment +difficulty: beginner +icon: scale +related: + - equipment/overview + - equipment/refractometer + - fundamentals/physical-properties +tags: + - equipment/sg + - specific-gravity + - density + - identification + - hydrostatic + +sections: + - title: Introduction + content: | + Specific gravity (SG) — also called relative density — is the ratio of a substance's weight + to the weight of an equal volume of water. It is a fundamental physical property that helps + identify gem species, particularly when refractive index and optical tests are inconclusive. + + SG measurement is a Foundation-required skill (Gem-A FS5) and a standard part of any + complete gemstone identification sequence. + + - title: Hydrostatic Balance Principle + content: | + The hydrostatic method applies Archimedes' principle: a body immersed in a liquid experiences + an upward buoyant force equal to the weight of the displaced liquid. + + **Formula:** + + > SG = W_air / (W_air − W_water) + + Where: + - **W_air** = weight of the stone in air (grams) + - **W_water** = apparent weight of the stone when fully immersed in water (grams) + - **(W_air − W_water)** = buoyancy force = weight of displaced water = weight of equal + volume of water + + The denominator is the key: it gives the weight of a volume of water equal to the stone's + volume, and dividing the stone's mass by that gives the density ratio relative to water. + + Farrimond (1994) provides a practical account of this method for gemmological use: + Journal of Gemmology 24(3), 161–163 (DOI: 10.15506/jog.1994.24.3.161) [VERIFIED]. + + - title: Equipment Setup + content: | + A standard hydrostatic SG setup uses readily available laboratory equipment. + subsections: + - title: Required Components + content: | + - **Analytical balance** — single-pan electronic or two-pan beam balance; ±0.01 g + resolution minimum (±0.001 g preferred for stones below 0.5 g) + - **Bridge or cradle frame** — mounted over or beside the balance pan; holds the beaker + of water while the stone hangs suspended below on a wire + - **Fine wire sling or fibre-basket** — suspends the stone fully immersed without + touching the beaker walls or base + - **Beaker of distilled water** with one drop of wetting agent (household detergent) to + reduce surface tension and prevent air bubbles + - **Thermometer** — for temperature corrections if precision is required + - **Tweezers** — for stone handling; avoid fingers which add grease + + - title: Procedure + content: | + 1. Tare the balance with the wire sling hanging freely in air above the beaker. + 2. Place the stone in the sling, lower it so it hangs freely in air. Record **W_air**. + 3. Raise the beaker of distilled water so the stone is fully immersed — check no + air bubbles are visible on the stone surface; gently agitate if needed. + 4. Record **W_water** (the apparent weight under water — numerically less than W_air). + 5. Calculate: **SG = W_air / (W_air − W_water)**. + 6. Repeat at least twice; take the mean. + + **Worked example:** W_air = 2.50 g; W_water = 1.60 g + → SG = 2.50 / (2.50 − 1.60) = 2.50 / 0.90 = 2.78 → consistent with beryl. + + - title: Temperature Corrections + content: | + Water density varies with temperature. At 4 °C the density is 1.0000 g/cm³ (the + standard reference). At 25 °C it is 0.9971 g/cm³. + + For most gemmological work (accuracy to ±0.02 SG units) no correction is needed at + typical room temperature (18–25 °C). For precision work, multiply the result by the + actual water density at the measured temperature. + + - title: Heavy Liquids for Rapid SG Bracketing + content: | + Heavy liquids are dense organic or inorganic liquids used for density-based separation + without weighing. A stone denser than the liquid sinks; a stone less dense floats; a stone + of equal density suspends (hovers mid-liquid). + + This gives a rapid qualitative SG bracket in seconds. Liquids may be diluted (with acetone + for organic liquids, or water for sodium polytungstate) to adjust density to intermediate + values. Shannon (1985) described the gemmological use of heavy liquids in Gems & Gemology + (DOI: 10.1080/00357529.1985.11764366) [PARTIALLY_SUPPORTED — title and DOI confirmed; + abstract not retrieved]. + table: + caption: Heavy Liquids Used in Gemmological Laboratories + headers: + - Liquid + - Common Name + - Density (g/cm³) + - Hazard Class + - Status + rows: + - ["Di-iodomethane (CH₂I₂)", "Methylene iodide", "~3.32 at 20 °C", "Toxic vapour; photodegrades; stains skin", "Still in common use — handle in fume cupboard"] + - ["Bromoform (CHBr₃)", "Bromoform", "~2.89 at 20 °C", "Toxic; suspected carcinogen; volatile", "Being phased out in many laboratories"] + - ["Clerici solution (thallium formate–malonate)", "Clerici", "Up to ~4.2 (adjustable)", "Acutely toxic — thallium absorbed through skin", "Banned or restricted in many jurisdictions; avoid"] + - ["Sodium polytungstate (Na₆[H₂W₁₂O₄₀])", "SPT", "~2.7–3.1 (adjustable with water)", "Non-toxic; water-soluble", "Modern alternative; does not reach 3.32+ SG range"] + + - title: Safety + callout: + type: warning + title: Heavy Liquid Hazards — Read Before Use + text: | + **Clerici solution** is the most dangerous heavy liquid used in gemmological laboratories. + It contains thallium salts; thallium is absorbed through intact skin and mucous membranes, + accumulates in the body, and is acutely toxic. Many UK laboratories have discontinued its + use under COSHH regulations. Where Clerici is still used: full PPE (nitrile gloves, fume + cupboard, closed containers) is mandatory. **Never use Clerici without training.** + + **Di-iodomethane:** toxic vapour — use in ventilated area or fume cupboard. + Photodegrades on exposure to light/air (turns brown/orange; store in amber bottles). + Can irreversibly stain organic gems (pearls, amber, coral) — not suitable for these. + + **Bromoform:** volatile, toxic, possible carcinogen; not to be used without fume cupboard. + + **Sodium polytungstate (SPT):** non-toxic modern alternative. Maximum achievable SG ~3.1; + cannot reach the 3.32+ range needed for separation near di-iodomethane threshold. + + Munsterman & Kerstholt (1996) introduced SPT as a "non-toxic alternative to bromoform": + Review of Palaeobotany and Palynology 91, 417–422 (DOI: 10.1016/0034-6667(95)00093-3) + [VERIFIED]. + + - title: SG Reference Values + content: | + These SG values are used to evaluate hydrostatic results and to predict sink/float behaviour + in heavy liquids. Values from the Gem-A Foundation constants table. + table: + caption: Common Gem Species SG Reference Values + headers: + - Species + - SG Range + - Behaviour in Di-iodomethane (SG 3.32) + - Behaviour in Bromoform (SG 2.89) + - Notes + rows: + - ["Diamond", "3.52", "Sinks", "Sinks", "Very consistent; cubic"] + - ["Corundum (ruby/sapphire)", "3.80–4.05", "Sinks", "Sinks", "Wide range due to Fe/Ti content"] + - ["Spinel (natural)", "3.58–3.61", "Sinks", "Sinks", "Isotropic"] + - ["Spinel (Verneuil synthetic)", "3.61–3.67", "Sinks", "Sinks", "Slightly higher than natural"] + - ["Topaz", "3.50–3.60", "Sinks", "Sinks", "Perfect basal cleavage — handle carefully"] + - ["Peridot", "3.32–3.37", "Floats / suspends", "Sinks", "SG overlaps di-iodomethane closely"] + - ["Jadeite", "3.30–3.36", "Floats / suspends", "Sinks", "Aggregate material"] + - ["Nephrite", "2.80–3.10", "Floats", "Floats / suspends", "Lower than jadeite — useful diagnostic"] + - ["Beryl (all varieties)", "2.65–2.80", "Floats", "Floats", "Includes emerald, aquamarine, morganite"] + - ["Quartz (crystalline)", "2.65", "Floats", "Floats", "Very consistent; useful balance calibration standard"] + - ["Amber", "1.05–1.10", "Floats", "Floats", "Floats in saturated salt water (SG ~1.13)"] + - ["Glass (paste)", "2.0–4.2", "Variable", "Variable", "Wide range depending on lead content"] + + - title: Sources of Error + content: | + The following errors are common in hydrostatic SG measurement: + subsections: + - title: Measurement Errors + content: | + - **Air bubbles on the stone surface** — reduce the apparent weight of displaced water, + giving a falsely high SG reading. Remove by gently agitating or by using a wetting + agent in the water. + - **Mounted stones** — metal settings introduce unknown mass; the method is unreliable + for set stones without dismounting. + - **Porous or treated stones** — water absorption (opal, turquoise, some coral) alters + the reading over time as the stone absorbs liquid. + - **Very small stones** — weighing error becomes proportionally large; minimum useful + stone weight is approximately 0.15–0.20 g for ±0.01 g balance resolution. + - **Fracture-filled stones** — filler material (glass, resin) changes the apparent SG + from the host mineral. + + - title: Balance Calibration + content: | + - Check balance calibration before each session using a stone of known SG. + - **Quartz (SG 2.65)** is a convenient and inexpensive reference standard. + - If readings on a reference stone deviate by more than ±0.02, recalibrate the balance + before continuing. + + - title: Sources + content: | + **Key citations for this topic:** + + - Farrimond, T. (1994). "Hydrostatic measurement of specific gravity." *The Journal of + Gemmology* 24(3), 161–163. DOI: 10.15506/jog.1994.24.3.161 [VERIFIED] + - Walton (1951). "A Specific Gravity Balance." *The Journal of Gemmology* 3(2), 43. + DOI: 10.15506/jog.1951.3.2.43 [VERIFIED] + - Mitchell (1980). "Anderson on Heavy Liquids." *The Journal of Gemmology* 17(4), 230. + DOI: 10.15506/jog.1980.17.4.230 [VERIFIED] + - Shannon (1985). "Determining Specific Gravity Using Heavy Liquids." *Gems & Gemology*. + DOI: 10.1080/00357529.1985.11764366 [PARTIALLY_SUPPORTED — title and DOI confirmed; + abstract not retrieved] + - Munsterman, D. & Kerstholt, S. (1996). "Sodium polytungstate, a new non-toxic alternative + to bromoform in heavy liquid separation." *Review of Palaeobotany and Palynology* 91, + 417–422. DOI: 10.1016/0034-6667(95)00093-3 [VERIFIED] + - Read, P. G. (ed.). *Gems* 7th ed., chapter "Specific gravity, density and relative + density." DOI: 10.4324/9780080507224-12 [VERIFIED] diff --git a/docs/learn/equipment/spectroscope.yaml b/docs/learn/equipment/spectroscope.yaml index 5812984..f069d64 100644 --- a/docs/learn/equipment/spectroscope.yaml +++ b/docs/learn/equipment/spectroscope.yaml @@ -8,6 +8,7 @@ related: - fundamentals/optical-properties - index - fundamentals/chemical-properties + - equipment/chelsea-colour-filter tags: - equipment/spectroscope - absorption-spectrum @@ -179,6 +180,72 @@ sections: - Some gem species show no diagnostic spectrum - Laboratory spectrometers provide more detailed analysis + - title: Named Absorption Spectra — Foundation Tier + content: | + The twelve species below form the core absorption-spectrum vocabulary for the FGA Foundation + examination. Each spectrum must be recognisable by principal line(s) and overall pattern. + + **Note on wavelength values:** Several nm values in this table are sourced from Read, + P. G. (ed.), *Gemmology* (commonly referenced as "Read 7th ed.", Butterworth-Heinemann), which + is the standard Gem-A teaching textbook. These values are [PARTIALLY_SUPPORTED] — the + chromophore assignments and general spectral patterns are confirmed by peer-reviewed + DOI-verified sources (Fritsch & Rossman 1987, DOI: 10.5741/gems.23.3.126; Dubinsky et al. + 2020, DOI: 10.5741/gems.56.1.2; Breeding & Shigley 2009, DOI: 10.5741/gems.45.2.96; + Karampelas et al. 2019, DOI: 10.3390/min9090561; Balciūnaite et al. 2021, + DOI: 10.6001/chemija.v32i3-4.4549; Phillips & Talantsev 1996, DOI: 10.5741/gems.32.2.100), + but the precise nm values for some secondary lines derive from the textbook and are not + independently verifiable via abstract APIs. + table: + caption: Foundation Tier — 12 Core Absorption Spectra + headers: + - Species + - Principal Lines (nm) + - Chromophore + - Diagnostic Strength + rows: + - ["Ruby (natural + Verneuil)", "692.8 + 694.2 doublet; 668, 659; broad ~550 absorption; 468; UV cutoff ~400", "Cr³⁺", "Highest — doublet + luminescent glow in red light"] + - ["Emerald (natural)", "683 + 680 doublet; 662, 646; broad ~580–630; blue-violet absorption; 477 (some stones)", "Cr³⁺ (± Fe³⁺ in Fe-rich stones)", "High — doublet diagnostic; Fe bands vary by origin"] + - ["Blue sapphire", "450 strong narrow; 460, 470 weaker; broad Fe²⁺–Ti⁴⁺ CT absorption", "Fe³⁺ + Fe²⁺–Ti⁴⁺ charge transfer", "High — 450 nm line in virtually all blue sapphire"] + - ["Almandine garnet", "504, 520, 573 broad bands; weaker 423, 461, 610, 680, 690", "Fe²⁺", "Highest — three-band pattern virtually diagnostic"] + - ["Pyrope garnet", "504, 520, 573 (Fe²⁺); chromiferous: broad ~575 + 685–687 (Cr³⁺)", "Fe²⁺ ± Cr³⁺", "Moderate — Fe bands shared with almandine"] + - ["Spessartine garnet", "410, 421, 432 strong (Mn²⁺); violet edge cutoff", "Mn²⁺", "Highest — Mn triplet unique to spessartine"] + - ["Demantoid garnet", "~440 nm cutoff (Fe³⁺); Russian type: 618, 634, 685, 701 (Cr³⁺)", "Fe³⁺ ± Cr³⁺", "High — 440 cutoff separates from green idocrase"] + - ["Peridot", "493, 473, 453 three evenly spaced bands (Fe²⁺)", "Fe²⁺", "Highest — three-iron-band pattern essentially diagnostic"] + - ["Zircon (high / Sri Lanka type)", "653.5 principal; 691, 662, 660, 621, 615, 589, 562, 537, 516, 484, 460 fine lines", "U⁴⁺", "Highest — picket-fence multi-line pattern unmistakeable"] + - ["Diamond (Cape series / Type Ia)", "415.5 (N3 centre); 478 (N2); 465, 451, 435, 423, 401 weaker vibronic series", "Nitrogen aggregate (N3, N2 defect centres)", "High — 415.5 nm canonical Cape yellow marker"] + - ["Red spinel (natural)", "656, 665, 685 narrow Cr³⁺ lines; broad ~540 absorption", "Cr³⁺", "High — organ pipe triplet separates from ruby (694 nm doublet)"] + - ["Zircon (low / metamict)", "653.5 diffuse or absent; featureless or very broad", "U⁴⁺ (amorphised lattice)", "Low — contrast with high zircon confirms metamict character"] + + - title: Named Absorption Spectra — Diploma Extension Tier + content: | + The sixteen species below extend the Foundation spectra list to Diploma level, covering + additional corundum varieties, tourmalines, secondary garnets, and selected rare species. + The same note on textbook-sourced nm values applies (see Foundation tier heading above). + table: + caption: Diploma Tier — 16 Extended Absorption Spectra + headers: + - Species + - Principal Lines (nm) + - Chromophore + - Diagnostic Strength + rows: + - ["Alexandrite (chrysoberyl)", "680.5 + 678.5 doublet; 655, 645; broad ~580 (colour-change band); broad ~420–450", "Cr³⁺", "High — doublet shifted from ruby (694 nm) and emerald (683 nm)"] + - ["Yellow sapphire", "450 (Fe³⁺, if present); broad tailing into violet; often absent in pale stones", "Fe³⁺ ± colour centre", "Low–moderate — spectrum often very weak; RI/SG primary"] + - ["Green sapphire", "471, 460, 450 (Fe²⁺/Fe³⁺)", "Fe²⁺ + Fe³⁺", "Moderate — modified blue sapphire pattern"] + - ["Padparadscha sapphire", "450 (Fe³⁺); broad violet colour-centre absorption", "Fe³⁺ + colour centre", "Low — combination not uniquely diagnostic; colour description primary"] + - ["Colombian vs Zambian emerald", "Colombia: Cr doublet 683/680, Fe bands weak/absent; Zambia: same doublet + stronger Fe absorption + possible 477 nm line", "Cr³⁺ ± Fe³⁺", "Moderate — Fe-band presence/absence aids origin discrimination; not conclusive alone"] + - ["Tsavorite garnet (chrome grossular)", "Broad ~630 (V³⁺/Cr³⁺); broad ~450; weak 433 (Mn²⁺ if present)", "V³⁺ ± Cr³⁺ ± Mn²⁺", "Moderate — no single sharp diagnostic line; RI/SG more reliable"] + - ["Rhodolite garnet (pyrope-almandine)", "504, 520, 573 (Fe²⁺); Cr³⁺ shoulder ~680–687 if chromiferous", "Fe²⁺ ± Cr³⁺", "Moderate — identical to almandine/pyrope; SG/RI differentiate"] + - ["Indicolite tourmaline", "Broad ~720 (Fe²⁺ d-d); broad UV cutoff 300–400 (O²⁻–Fe³⁺ CT)", "Fe²⁺ + Fe²⁺–Fe³⁺ IVCT", "Moderate — gradual cutoff, no sharp lines; contrast with blue sapphire 450 nm line"] + - ["Rubellite tourmaline", "Broad ~520 (Mn³⁺); no sharp lines", "Mn³⁺", "Moderate — broad green absorption; no lines (contrast with red spinel organ pipe)"] + - ["Chrome tourmaline", "~680 (Cr³⁺); broad green/blue absorption", "Cr³⁺", "Moderate–high — Cr line position less sharp than ruby or emerald"] + - ["Aquamarine (blue beryl)", "537, 456, 427 (Fe²⁺ + Fe³⁺); often weak", "Fe²⁺ + Fe³⁺", "Low–moderate — spectrum frequently faint in pale stones"] + - ["Tanzanite (heat-treated blue zoisite)", "Broad ~450–460 (V³⁺ along α-axis); broad ~520 (V³⁺)", "V³⁺ ± Ti³⁺/⁴⁺", "Moderate — broad V band; trichroism is stronger diagnostic indicator"] + - ["Jadeite", "437 narrow (Fe³⁺, most jadeite); imperial green: broad ~630–650 + ~690 (Cr³⁺)", "Fe³⁺ ± Cr³⁺", "Moderate — 437 nm separates from nephrite (which lacks this line)"] + - ["Chrome diopside", "Broad ~670 (Cr³⁺); ~690 narrow-moderate Cr R-lines", "Cr³⁺", "Moderate — broad 670 band similar to but distinguishable from ruby and demantoid"] + - ["Sphene (titanite)", "~580–585 doublet (Nd³⁺ + Pr³⁺ REE); additional sharp REE lines", "Nd³⁺, Pr³⁺ (rare earth)", "Moderate — didymium REE pattern + extraordinary dispersion makes misidentification unlikely"] + - ["Synthetic emerald (flux, e.g. Chatham) vs natural", "Cr doublet 683/680 present; Fe-related bands (477 nm, blue-violet) absent or very weak", "Cr³⁺ (Fe absent)", "Moderate — Fe-band absence supports synthetic; also consistent with Fe-poor Colombian natural; microscopy required for confirmation"] + - title: Try the Interactive Tool callout: type: tip diff --git a/docs/learn/fundamentals/colour-theory.yaml b/docs/learn/fundamentals/colour-theory.yaml new file mode 100644 index 0000000..41b0b1a --- /dev/null +++ b/docs/learn/fundamentals/colour-theory.yaml @@ -0,0 +1,395 @@ +title: Colour Theory in Gemmology +description: The physics and chemistry of gem colour — crystal field theory, charge transfer, colour centres, allochromatic and idiochromatic minerals, and band-gap colouration. +order: 3.2 +category: fundamentals +difficulty: advanced +icon: palette +related: + - fundamentals/optical-properties + - fundamentals/chemical-properties + - fundamentals/optical-properties-advanced + - equipment/spectroscope +tags: + - colour-cause + - crystal-field-theory + - charge-transfer + - colour-centres + - idiochromatic + - allochromatic + +sections: + - title: Overview — The Four Main Causes of Colour + content: | + Kurt Nassau's classification (Nassau, *The Physics and Chemistry of Color*, 2nd ed., 2001) + identifies fifteen mechanisms of colour in minerals, of which four are central to gemmology: + + 1. **Crystal field theory (d–d transitions)** — the dominant mechanism for chromophore transition + metals in most coloured gem species (Cr³⁺ in ruby and emerald, Fe²⁺ in peridot). + 2. **Charge transfer** — electron transfer between adjacent ions; responsible for blue sapphire + and aquamarine colour. + 3. **Colour centres** — defects in the crystal lattice that trap electrons or holes and absorb + visible light; responsible for smoky quartz, amethyst, blue topaz, and coloured diamond. + 4. **Band-gap (semiconductor) absorption** — the entire conduction band absorbs photons above + the gap energy; explains the pure colourlessness of type IIa diamond and the vivid red of + cinnabar. + + Understanding which mechanism operates in a given stone allows the gemmologist to interpret + spectroscope data, Chelsea Colour Filter reactions, fluorescence, and treatment susceptibility. + + - title: Crystal Field Theory and d–d Transitions + content: | + Crystal field theory (CFT) describes how the electrostatic field of surrounding ligand anions + (usually O²⁻) splits the five degenerate d-orbitals of a transition-metal cation into two + energy sub-sets. When an electron absorbs a photon to jump between sub-sets, the remaining + transmitted wavelengths constitute the body colour. + + **Mechanism:** + - In an octahedral coordination site (6 O²⁻ ligands), the d-orbitals split into a lower set + (t₂g) and a higher set (eɡ), separated by the crystal field splitting energy Δ_oct. + - In a tetrahedral site (4 ligands), the splitting Δ_tet ≈ 4/9 Δ_oct — smaller, producing + weaker colour. + - The energy Δ determines the absorbed wavelength (E = hc/λ); a larger Δ absorbs shorter, + higher-energy wavelengths. + - The same chromophore ion produces different colours in different host structures, because + Δ depends on coordination number, bond length, and the nature of the coordinating anion. + - Cr³⁺ has strong absorption in the blue–green and a weaker band in the yellow; what + survives is deep red to pink. The exact energies are host-dependent. + + **Key diagnostic character:** d–d transitions produce broad, smoothly curved absorption + bands in the visible, distinguishable from the sharp lines of colour centres and the steep + asymmetric edges of charge transfer. + + *Source: Nassau, pp. 101–153 [VERIFIED]; Read 3rd ed., DOI: 10.4324/9780080507224 [VERIFIED]* + subsections: + - title: Ruby — Cr³⁺ in corundum (Al₂O₃) + content: | + Al³⁺ octahedral sites are comparatively small; the strong field around Cr³⁺ gives Δ_oct + large enough to produce broad absorption at ~410 nm (violet–blue) and ~560 nm (yellow–green), + leaving deep red transmitted. + + Cr³⁺ also produces a characteristic sharp emission (fluorescence) doublet at ~692–694 nm + (the "R lines"), visible in the absorption spectrum as the ruby doublet and responsible for + the internal red "fire" of Mogok rubies when illuminated with a tungsten source. + + **Chelsea Colour Filter reaction:** strongly red (Cr³⁺ transmits deep red and absorbs green). + + - title: Emerald — Cr³⁺ in beryl (Be₃Al₂Si₆O₁₈) + content: | + The same Cr³⁺ ion sits in a slightly larger Al³⁺ octahedral site in beryl compared with + corundum, shifting Δ to smaller values. The absorption bands move to slightly longer + wavelengths (~430 nm and ~610 nm), broadening the transmission window into green and + reducing fluorescence efficiency relative to ruby. + + V³⁺ in some Brazilian emeralds produces a similar but slightly weaker green via an + identical d–d mechanism. Chrome emeralds appear red through the Chelsea Colour Filter; + vanadium emeralds may appear red–orange or inert depending on V concentration. + + - title: Alexandrite — dual transmission window + content: | + Alexandrite (Cr³⁺ in chrysoberyl, BeAl₂O₄) is the classic example of the alexandrite + effect. The Cr³⁺ crystal field in chrysoberyl produces two transmission windows — + one in the red (~680 nm) and a narrower one in the blue–green (~580 nm region excluded + and ~470–490 nm transmitted). + + Under daylight (photopic peak ~555 nm), the blue–green window dominates → green. + Under incandescent light (spectral peak shifted toward 600 nm), the red window + dominates → red–purple. The colour change depends on which window the illuminant's + spectral peak falls nearest. + + *Source: Nassau 2001, pp. 112–115 [PARTIALLY_SUPPORTED]; F-009 confirmed in principle* + + - title: Peridot — Fe²⁺ in olivine + content: | + Fe²⁺ in the M1 and M2 octahedral sites of olivine (Mg₂SiO₄) produces three distinct + absorption bands at approximately 493 nm, 473 nm, and 453 nm — the classic three-banded + iron spectrum visible in the spectroscope. The yellow-green colour results from this + triplet absorbing blue and leaving yellow-green transmitted. + + The relatively weak crystal field around Fe²⁺ in olivine results in smaller Δ values + compared with Cr³⁺ in corundum, which is why the colour is yellow-green rather than red. + + **Peridot is idiochromatic** — Fe²⁺ is an essential constituent of gem-quality olivine. + + *Source: Nassau, pp. 108–112 [VERIFIED]* + + - title: Charge-Transfer Colouration + content: | + Charge transfer (CT) colour arises when an electron is transferred between two adjacent ions + — either between two metal ions (intervalence charge transfer, IVCT) or from oxygen to a + metal (ligand-to-metal charge transfer, LMCT) — rather than remaining on a single ion as + in d–d transitions. + + **Mechanism:** + - **Heteronuclear IVCT:** Fe²⁺–Ti⁴⁺ pairs on alternating face-sharing octahedral sites + along the c-axis of corundum. Under photon absorption: + Fe²⁺ + Ti⁴⁺ + hν → Fe³⁺ + Ti³⁺. Absorbs strongly from blue through yellow–green, + leaving blue–violet transmitted. + - **Homonuclear IVCT:** Fe²⁺ + Fe³⁺ on adjacent sites: + Fe²⁺ + Fe³⁺ + hν → Fe³⁺ + Fe²⁺. Absorbs in yellow–red, leaving blue transmitted. + - **LMCT:** Electron transfer from O²⁻ to an empty d-orbital of Fe³⁺ absorbs in the UV + and tails into the visible, producing yellow or orange. + - CT transitions have much higher extinction coefficients than d–d transitions; trace + concentrations of CT-capable pairs (~0.01% Ti in sapphire) suffice for intense colour. + - CT bands are broad and asymmetric, without the sharp emission lines of Cr³⁺. + + *Source: Nassau, pp. 184–210 [VERIFIED]; Dubinsky 2020, DOI: 10.5741/gems.56.1.2 [VERIFIED]* + subsections: + - title: Blue sapphire — Fe²⁺–Ti⁴⁺ IVCT in corundum + content: | + Nassau's canonical IVCT example. The Fe–Ti pair on alternating face-sharing octahedral + sites absorbs strongly in the yellow–red (peaking ~550–700 nm), leaving blue–violet + transmitted. Spectroscope shows three broad, unresolved bands at approximately 450 nm, + 460 nm, and 470 nm — the diagnostic blue sapphire triplet. + + No sharp Cr fluorescence lines; no red CCF reaction (no Cr³⁺ unless the sapphire is + deliberately Cr-bearing, as in some Sri Lanka padparadscha). + + *Source: Dubinsky et al. 2020, DOI: 10.5741/gems.56.1.2 [VERIFIED]* + + - title: Aquamarine — Fe²⁺–Fe³⁺ IVCT in beryl + content: | + Fe²⁺ and Fe³⁺ on adjacent sites in the beryl channel structure produce a broad + absorption band in the yellow–red, leaving blue transmitted. The spectroscope shows + a broad unresolved band without sharp lines. + + Indicolite tourmaline (blue) carries a similar Fe²⁺–Fe³⁺ IVCT colour. Kyanite blue + is also attributed to this IVCT mechanism. + + - title: Yellow sapphire — Fe³⁺ LMCT + content: | + Fe³⁺ alone (without Ti⁴⁺ to form IVCT pairs) absorbs in the UV, with the absorption + tail cutting into the blue end of the visible, leaving yellow–orange transmitted. + Some orange sapphires combine Fe³⁺ LMCT with Cr³⁺ d–d bands. + + - title: Diagnostic contrast — CT vs d–d + content: | + A gemmologist can distinguish CT-coloured stones from d–d-coloured stones by: + + - **Spectroscope:** CT gives broad, asymmetric bands; d–d gives narrower, more + symmetrical bands; Cr³⁺ gives narrow sharp emission doublet at 692–694 nm. + - **CCF:** CT blue sapphire appears inert to green (no Cr); Cr³⁺ stones appear red. + - **Fluorescence:** Cr³⁺ ruby fluoresces strongly red under LWUV; Fe²⁺–Ti⁴⁺ + sapphire is typically inert or shows weak orange. + + - title: Colour Centres + content: | + A colour centre is a localised lattice defect — typically an electron (F-centre) or a hole + (h-centre) trapped at a structural imperfection such as an anion vacancy or adjacent to a + substitutional impurity — that absorbs visible light and creates colour in an otherwise + colourless material. + + **Mechanism:** + - **F-centre (Farbe = colour):** an anion vacancy trapping one or more electrons. The + trapped electron absorbs photons to move between energy levels of the defect potential. + - **Hole centre:** an unpaired electron hole trapped adjacent to a substitutional cation. + In quartz, Al³⁺ substituting for Si⁴⁺ creates a charge imbalance; irradiation leaves an + AlO₄ unit with a trapped hole — the [AlO₄]⁰ centre. + - **Irradiation** (natural γ/α/β or artificial neutron/electron beam) creates centres by + displacing atoms and generating vacancies. The stability of the centre determines whether + colour is permanent or fades. + - **Heat bleaching:** raising temperature allows trapped electrons/holes to escape and + recombine, destroying the centre. Smoky quartz bleaches at ~300–400 °C; amethyst converts + to citrine at ~450–500 °C; irradiated blue topaz would bleach at high heat. + + *Source: Nassau, pp. 211–250 [VERIFIED]; Nassau & Prescott 1977, + DOI: 10.1180/minmag.1977.041.319.01 [VERIFIED]* + subsections: + - title: Smoky quartz — Al–O hole centre + content: | + Al³⁺ substituting for Si⁴⁺ in quartz, combined with natural or artificial irradiation, + produces a hole trapped at the AlO₄ unit (the [AlO₄]⁰ centre). Nassau & Prescott (1977) + demonstrated that the smoky colour arises from the A₃ absorption band at ~2.90 eV (~428 nm). + + Heating above 300–380 °C bleaches the centre, converting smoky quartz to colourless. + + *Source: Nassau & Prescott 1977, DOI: 10.1180/minmag.1977.041.319.01 [VERIFIED]* + + - title: Amethyst — Fe⁴⁺ hole centre + content: | + Fe³⁺ substituting for Si⁴⁺ in quartz, under irradiation, produces an [FeO₄]⁰ centre + (Fe⁴⁺ — a hole localised on iron). This centre absorbs at ~520 nm (green), transmitting + purple-violet. + + Heating above ~450 °C converts Fe⁴⁺ back to Fe³⁺, producing yellow citrine. This + transformation is exploited commercially to produce heat-treated citrine from amethyst. + + - title: Blue topaz — irradiation-induced colour centres + content: | + Natural blue topaz is rare. Commercial blue topaz is produced by neutron or electron + irradiation of colourless topaz, creating colour centres that absorb in the yellow–red + region. The colour is stable at room temperature but bleaches at high heat. + + The irradiated origin must be disclosed in trade (treated material). The colour mechanism + distinguishes blue topaz (colour centre, heat-sensitive) from aquamarine (Fe IVCT, stable). + + - title: Diamond colour centres — N3, NV, H3 + content: | + Nitrogen defects in diamond create several named optical centres: + + - **N3 centre** (three N atoms + vacancy): responsible for Cape blue-white fluorescence + under LWUV and the 415 nm absorption line (Cape series). Characteristic of type Ia + diamond — the most common natural diamond type. Spectroscopic literature gives 415.5 nm + for the zero-phonon line. + - **NV⁻ centre** (nitrogen–vacancy pair, negative charge): zero-phonon line at 637 nm; + produces pink to red photoluminescence. Found in pink diamonds and exploited in + quantum sensing applications. + - **NV⁰ centre** (neutral charge state): zero-phonon line at 575 nm. + - **H3 centre** (two N atoms + vacancy): zero-phonon line at 503 nm (503.2 nm in + spectroscopic precision); produces green–yellow fluorescence; found in HPHT-treated + diamonds. Detected by photoluminescence at 77 K. + + HPHT treatment of brown type IIa diamond anneals out vacancy-related brown centres, + destroying N3 characteristic fluorescence — detectable by FTIR and DiamondView. + + *Source: Hainschwang 2012, DOI: 10.5741/gems.48.4.252 [VERIFIED]; Nassau 2001, + pp. 227–235 [VERIFIED]* + + - title: Maxixe beryl — unstable colour centre + content: | + Deep blue beryl from the Maxixe mine, Minas Gerais, Brazil, owes its colour to an + irradiation-induced colour centre (involving NO₃⁻ or CO₃²⁻ radical anions substituting + in the beryl channel — the precise identity remains under study). + + The centre is unstable in ambient light and fades to pale pink or colourless over months + of daylight exposure — the gemmological standard case of light-bleachable colour. + This distinguishes maxixe beryl from aquamarine (Fe IVCT, stable) and irradiated blue + topaz (different centre, stable at room temperature). + + **Duty to advise:** a gemmologist identifying maxixe beryl must advise the client that + the colour will fade in sunlight, as this is a material fact affecting value. + + *Source: Adamo 2008, DOI: 10.5741/gems.44.3.214 [VERIFIED]* + + - title: Fluorite colour centres + content: | + Purple, golden, and blue fluorite owes its colour to electrons and holes trapped at Ca²⁺ + vacancies and interstitial F⁻ defects; natural irradiation from uranium-bearing inclusions + is often responsible. Colour is bleachable by heat. Fluorite's own very low dispersion + (0.007) gives it a "dead" optical appearance despite sometimes vivid colour. + + *Source: Nassau, pp. 215–218 [VERIFIED]* + + - title: Allochromatic, Idiochromatic, and Pseudochromatic + content: | + Three categories describe whether colour is essential to a mineral species or incidental. + + - **Allochromatic:** the pure end-member is colourless; colour depends on trace chromophore + impurities. The same mineral can appear in many colours. Removal of the impurity would + restore colourlessness. + - **Idiochromatic:** the colouring element is a required component of the mineral formula. + Even an ideal, pure crystal will be coloured. The colour range is narrow. + - **Pseudochromatic:** colour-like effects produced by light interference, diffraction, or + scattering — not electronic absorption. No chromophore is involved; the apparent colour + changes with viewing angle or disappears when the specimen is oriented edge-on. + + *Source: Nassau, pp. 100–104 [VERIFIED]* + subsections: + - title: Allochromatic examples + table: + headers: + - Mineral + - Pure form + - Chromophore → colour + rows: + - ["Corundum (Al₂O₃)", "White sapphire (colourless)", "Cr³⁺ → ruby; Fe²⁺+Ti⁴⁺ → blue sapphire; Fe³⁺ → yellow; Cr+Fe → padparadscha"] + - ["Beryl (Be₃Al₂Si₆O₁₈)", "Goshenite (colourless)", "Cr/V → emerald; Fe²⁺ → aquamarine; Mn → morganite; Fe³⁺ → heliodor"] + - ["Quartz (SiO₂)", "Rock crystal (colourless)", "Al³⁺ + irradiation → smoky; Fe⁴⁺ + irradiation → amethyst; Fe³⁺ thermal → citrine"] + + - title: Idiochromatic examples + table: + headers: + - Mineral + - Essential chromophore + - Colour + rows: + - ["Peridot / gem olivine ((Mg,Fe)₂SiO₄)", "Fe²⁺ essential to composition", "Yellow-green; cannot exist colourlessly"] + - ["Malachite (Cu₂(CO₃)(OH)₂)", "Cu²⁺ essential", "Always green from Cu²⁺ d–d absorption"] + - ["Turquoise (CuAl₆(PO₄)₄(OH)₈·4H₂O)", "Cu²⁺ essential", "Always blue-green; more Fe → greener"] + + - title: Pseudochromatic examples + table: + headers: + - Mineral/Phenomenon + - Cause + - Notes + rows: + - ["Precious opal (play-of-colour)", "Bragg diffraction from ordered silica sphere arrays (~150–300 nm)", "Colours shift with angle; no chromophore"] + - ["Labradorite (labradorescence)", "Thin-film interference in lamellar feldspar intergrowth (Bøggild intergrowth)", "Structural colour; changes with angle"] + - ["Moonstone (adularescence)", "Scattering + interference at thin albite lamellae within orthoclase", "Billowing blue sheen; not absorbed colour"] + + - title: Band-Gap Colouration + content: | + In crystalline solids with a band structure, colour arises when the band gap (Eg — the energy + difference between the valence band and the conduction band) falls within or near the visible + range. Photons with energy > Eg are absorbed; those with energy < Eg are transmitted. + + **Mechanism:** + - Pure diamond has Eg ≈ 5.47 eV, corresponding to ~227 nm (deep UV). All visible photons + pass through → pure type IIa diamond is colourless. + - When nitrogen or boron substitutes for carbon, new energy levels appear inside the gap, + allowing selective visible absorption. + - In semiconductors such as cinnabar, the gap itself falls in the visible range, giving a + sharp absorption edge. + + *Source: Nassau, pp. 253–275 [VERIFIED]; Read 3rd ed., DOI: 10.4324/9780080507224 [VERIFIED]* + subsections: + - title: Diamond type classification and colour + table: + caption: Diamond type, nitrogen/boron configuration, and colour + headers: + - Type + - Nitrogen/Boron configuration + - Body colour + - Notes + rows: + - ["Type Ia (most common)", "N in aggregated A and B centres", "Colourless to Cape yellow–brown", "N3 centre at 415 nm absorbs blue → yellow"] + - ["Type Ib (rare natural; common synthetic)", "Single substitutional N", "Canary yellow (intense)", "N donor level absorbs blue ~430 nm"] + - ["Type IIa (rarest natural)", "Essentially no N or B", "Colourless", "Largest diamonds (Cullinan); HPHT treatment target"] + - ["Type IIb (rare)", "B acceptors; no N", "Blue (e.g. Hope Diamond)", "P-type semiconductor; electrically conductive"] + + - title: Band-gap materials beyond diamond + table: + headers: + - Material + - Band gap / absorption + - Body colour + rows: + - ["Cinnabar (HgS)", "Eg ≈ 2.0 eV (~620 nm); blue–green absorbed", "Vivid red; SG 8.0–8.2"] + - ["Realgar (As₄S₄)", "Eg absorbs violet and blue", "Orange-yellow"] + - ["Orpiment (As₂S₃)", "Eg absorbs blue-violet", "Lemon yellow"] + + - title: Diagnostic Relevance + content: | + A gemmologist uses colour-cause knowledge at multiple practical points: + + - **Chelsea Colour Filter interpretation:** Cr³⁺ (d–d, CFT) → red; Fe²⁺–Ti⁴⁺ CT blue + sapphire → inert; S₃⁻ colour centre in hauyne → inert. + - **Treatment detection:** Colour-centre stones (smoky quartz, blue topaz, maxixe beryl, + irradiated diamond) are heat-sensitive. Knowing the mechanism identifies which treatments + could destroy or alter the colour. + - **Advising clients:** Maxixe beryl fades in light; irradiated blue topaz is stable at + room temperature but not at jewellery-repair temperatures. These are material disclosure + facts. + - **Spectroscope interpretation:** d–d transitions → broad bands; CT → asymmetric bands; + colour centres → sharp zero-phonon lines (in diamond photoluminescence); all contrasted + with sharp Cr³⁺ doublet at 692–694 nm. + - **Simulant/treatment separation:** diamond type classification by FTIR (N content), + optic character, and UV response is a direct application of band-gap/colour-centre theory. + + - title: Sources + content: | + - Nassau, K. *The Physics and Chemistry of Color*, 2nd ed. Wiley-Interscience, 2001. + ISBN 978-0-471-39106-7. Chapter DOI: 10.1016/b978-044451251-2/50008-8. [VERIFIED] + - Read, P. *Gemmology*, 3rd ed. Routledge, 2012. DOI: 10.4324/9780080507224. [VERIFIED] + - Nassau, K.; Prescott, B.E. "Smoky, blue, greenish yellow, and other irradiation-related + colors in quartz." *Mineralogical Magazine*, 41(319), 1977. + DOI: 10.1180/minmag.1977.041.319.01. [VERIFIED] + - Hainschwang, T. et al. "Photoluminescence at 77K in treated diamond." *Gems & Gemology*, + 48(4), 2012. DOI: 10.5741/gems.48.4.252. [VERIFIED] + - Dubinsky, E.V. et al. "Fe²⁺–Ti⁴⁺ charge transfer in blue sapphire." *Gems & Gemology*, + 56(1), 2020. DOI: 10.5741/gems.56.1.2. [VERIFIED] + - Adamo, I. et al. "Maxixe-type color in beryl." *Gems & Gemology*, 44(3), 2008. + DOI: 10.5741/gems.44.3.214. [VERIFIED] + - Dubey, S.; Rai, A.K. et al. "Mineralogical application of LIBS: idiochromatic, + allochromatic and pseudochromatic stones." *Journal of Optics*, 2022. + DOI: 10.1007/s12596-022-00870-8. [PARTIALLY_SUPPORTED] diff --git a/docs/learn/fundamentals/crystal-systems.yaml b/docs/learn/fundamentals/crystal-systems.yaml index c5d5154..f0ac9da 100644 --- a/docs/learn/fundamentals/crystal-systems.yaml +++ b/docs/learn/fundamentals/crystal-systems.yaml @@ -228,3 +228,187 @@ sections: - Peridot - Chrysoberyl - Tanzanite + + - title: The 32 Point Groups + content: | + A point group is the set of symmetry operations (rotation axes, mirror planes, inversion + centre) that leave at least one point of a crystal unmoved. There are exactly 32 unique + combinations possible in crystals (the 32 crystal classes), expressed in Hermann–Mauguin + (H–M) notation. + + **Key notational elements:** + - **n** = n-fold rotation axis (2, 3, 4, or 6) + - **m** = mirror plane + - **n̄** = rotoinversion axis (improper rotation) + - **1̄** = inversion centre + - **n/m** = rotation axis perpendicular to a mirror plane + + Point groups determine whether a crystal can be piezoelectric (no centre of inversion), + pyroelectric (polar point group), or optically active (enantiomorphic point group). + + The gem species assignments below are drawn from standard mineralogical sources. Where + no common gem species is assigned to a class, the entry is shown as a dash; these classes + exist and are crystallographically established even without a prominent gem example. + + *Source: Schwarzenbach, Journal of Applied Crystallography, 2003. + DOI: 10.1107/s0021889803014778 [VERIFIED]; Read 3rd ed. + DOI: 10.4324/9780080507224 [VERIFIED]* + table: + caption: The 32 Point Groups with gem species examples + headers: + - System + - Point Group (H–M) + - Type + - Gem Example + rows: + - ["Cubic", "23", "Enantiomorphic", "—"] + - ["Cubic", "m3̄", "Centrosymmetric", "Pyrite"] + - ["Cubic", "432", "Enantiomorphic", "—"] + - ["Cubic", "4̄3m", "Non-centrosymmetric", "Diamond (some); sphalerite"] + - ["Cubic", "m3̄m", "Holohedral (holosymmetric)", "Diamond (most gem diamonds); garnet; fluorite; spinel"] + - ["Tetragonal", "4", "Polar", "—"] + - ["Tetragonal", "4̄", "Non-centrosymmetric", "—"] + - ["Tetragonal", "4/m", "Centrosymmetric", "Scheelite"] + - ["Tetragonal", "422", "Enantiomorphic", "—"] + - ["Tetragonal", "4mm", "Polar", "—"] + - ["Tetragonal", "4̄2m", "Non-centrosymmetric", "Chalcopyrite"] + - ["Tetragonal", "4/mmm", "Holohedral", "Zircon; rutile; cassiterite; vesuvianite"] + - ["Orthorhombic", "222", "Enantiomorphic", "—"] + - ["Orthorhombic", "mm2", "Polar", "—"] + - ["Orthorhombic", "mmm", "Holohedral", "Topaz; peridot/olivine; tanzanite/zoisite; andalusite; danburite"] + - ["Trigonal", "3", "Polar, enantiomorphic", "—"] + - ["Trigonal", "3̄", "Centrosymmetric", "—"] + - ["Trigonal", "32", "Enantiomorphic", "Quartz (explains optical activity — left/right handed)"] + - ["Trigonal", "3m", "Polar", "Tourmaline (piezoelectric/pyroelectric); calcite group"] + - ["Trigonal", "3̄m", "Holohedral", "Corundum (ruby, sapphire); hematite"] + - ["Hexagonal", "6", "Polar, enantiomorphic", "—"] + - ["Hexagonal", "6̄", "Non-centrosymmetric", "—"] + - ["Hexagonal", "6/m", "Centrosymmetric", "Apatite"] + - ["Hexagonal", "622", "Enantiomorphic", "—"] + - ["Hexagonal", "6mm", "Polar", "Wurtzite"] + - ["Hexagonal", "6̄m2", "Non-centrosymmetric", "Benitoite"] + - ["Hexagonal", "6/mmm", "Holohedral", "Beryl (emerald, aquamarine, morganite)"] + - ["Monoclinic", "2", "Polar, enantiomorphic", "—"] + - ["Monoclinic", "m", "Polar", "—"] + - ["Monoclinic", "2/m", "Centrosymmetric", "Orthoclase/microcline; diopside; jadeite; spodumene; malachite"] + - ["Triclinic", "1", "Polar", "—"] + - ["Triclinic", "1̄", "Centrosymmetric", "Labradorite/plagioclase; kyanite; rhodonite; turquoise"] + + - title: Point Group Notes + content: | + Several point groups have gemmologically significant consequences: + + - **Quartz (point group 32):** the enantiomorphic class explains why quartz is optically + active (rotates plane of polarisation), exists as left-handed and right-handed crystals, + and shows the Brazil and Dauphiné twin laws. No centre of inversion → piezoelectric. + - **Tourmaline (point group 3m):** polar axis along c responsible for piezoelectricity and + pyroelectricity. The polar nature also produces pyroelectric discharge when temperature + changes — tourmaline crystals attract dust. + - **Corundum (point group 3̄m):** has a centre of inversion (the 3̄ inversion axis); + therefore neither piezoelectric nor optically active. Uniaxial negative with pleochroism + oriented along the c-axis. + - **Diamond (point group m3̄m):** highest possible cubic symmetry (Oh); isotropic; single RI; + no birefringence, no pleochroism. + - **Benitoite (point group 6̄m2):** hexagonal symmetry class; notable for intense SWUV + fluorescence and dispersion equal to diamond (0.044); uniaxial positive. + + callout: + type: info + title: Point Group vs Crystal System + text: | + Each crystal system contains multiple point groups — not a single one. A crystal system + defines the axial geometry; the point group specifies the exact symmetry elements present. + For example, the trigonal system contains point groups 3, 3̄, 32, 3m, and 3̄m — each + giving different physical properties (optical activity, piezoelectricity, centrosymmetry). + + - title: Miller Indices — 3-Index and 4-Index Notation + content: | + Miller indices {hkl} describe the orientation of a crystal face or plane by the reciprocals + of its fractional intercepts on the crystallographic axes. + + **Three-index notation {hkl}** — used for cubic, tetragonal, orthorhombic, monoclinic, and + triclinic systems (three axes: a, b, c): + - {100}: intercepts a at 1, parallel to b and c. + - {111}: intercepts all three axes equally — the octahedral face in cubic. + - {110}: intercepts a and b at 1, parallel to c — the dodecahedral face in cubic. + + **Four-index (Bravais–Miller) notation {hkil}** — required for trigonal and hexagonal + systems, which have three equivalent horizontal axes (a₁, a₂, a₃) at 120° and one vertical + c-axis: + - The **closure relation** i = −(h+k) always holds; i is not an independent variable but + makes the symmetry equivalence of faces explicit in the notation. + - {10-10}: the hexagonal prism face. i = -(1+0) = -1, confirming h + k + i = 0. + - {0001}: the basal pinacoid — perpendicular to the c-axis; the "table" of a hexagonal crystal. + - {10-11}: the rhombohedral face in trigonal — the twin and parting plane of corundum. + + **Why the redundant index?** In a 6-fold-symmetric hexagonal crystal there are six + equivalent prism faces. The 4-index notation makes this equivalence explicit: {10-10}, + {01-10}, {-1100}, {-1010}, {0-110}, {1-100} are all the same form, and the notation + allows this to be seen by inspection. + + *Source: Schwarzenbach, Journal of Applied Crystallography, 2003. + DOI: 10.1107/s0021889803014778 [VERIFIED]* + subsections: + - title: Worked examples + table: + headers: + - Crystal / face + - Notation + - Notes + rows: + - ["Cubic diamond, octahedral face", "{111}", "Three equal intercepts on a, b, c"] + - ["Cubic diamond, cube face", "{100}", "Intersects a; parallel to b and c"] + - ["Quartz (trigonal), prism face", "{10-10}", "Four-index; i = -(1+0) = -1; the common m-face"] + - ["Quartz, pyramid face", "{10-11}", "Four-index; also the rhombohedral face r"] + - ["Corundum, basal pinacoid", "{0001}", "Perpendicular to c; parting plane"] + - ["Corundum, rhombohedral parting", "{10-11}", "Twin and parting plane; four-index required (trigonal)"] + + - title: Examination note + content: | + The distinction between 3-index and 4-index notation is a common examination point at + Diploma level. The only formula to remember is: **i = −(h+k)**. + + Understanding this relation explains why trigonal/hexagonal crystals have 6-fold or + 3-fold equivalence of side faces — each set of equivalent faces has the same set of + |h|, |k|, |i| values in different permutations. + + - title: Parting (False Cleavage) + content: | + Parting is a tendency for a crystal to break along planes that are not true cleavage planes. + It resembles cleavage (producing flat, reflective fracture surfaces) but is caused by + repeated twinning lamellae or by exsolution of a second phase along a crystallographic plane. + + **Distinction from cleavage:** + - **Cleavage** is universal — every crystal of the species will cleave along the same planes, + because the planes reflect inherently weak bonds in the crystal structure. + - **Parting** is contingent — only crystals that happen to be twinned or to have undergone + exsolution show parting. It may be restricted to parts of the crystal and is not universal + across all specimens of the species. + + *Source: Read 3rd ed. DOI: 10.4324/9780080507224 [VERIFIED]; + Pignatelli 2024, DOI: 10.1007/s00710-024-00858-1 [VERIFIED]* + subsections: + - title: Corundum parting + content: | + Corundum (ruby and sapphire) has no true cleavage. It shows two parting directions from + polysynthetic twinning: + + - **{10-11} rhombohedral parting** — the most prominent; arises from repeated polysynthetic + twinning on the rhombohedral plane. Visible as parallel flat steps on broken corundum + rough, and as iridescent flat internal planes in faceted stones. + - **{0001} basal parting** — from twinning on the basal pinacoid; less consistent. + + A common Diploma examination error is stating "corundum has perfect basal cleavage." + The correct answer is: corundum has **no cleavage**; the flat surfaces observed are + parting along twin planes. + + - title: Other parting examples + table: + headers: + - Mineral + - Parting plane + - Cause + rows: + - ["Corundum (ruby, sapphire)", "{10-11} and {0001}", "Polysynthetic twinning on those planes"] + - ["Pyroxene (diopside, enstatite)", "{100}", "Exsolution or twinning; combined with {110} cleavage gives two-direction breakage"] + - ["Magnetite", "{111}", "Spinel-law twinning; relevant when magnetite is an inclusion"] diff --git a/docs/learn/fundamentals/optic-sign-determination.yaml b/docs/learn/fundamentals/optic-sign-determination.yaml new file mode 100644 index 0000000..ed658ed --- /dev/null +++ b/docs/learn/fundamentals/optic-sign-determination.yaml @@ -0,0 +1,194 @@ +title: Optic Sign Determination +description: Determining positive or negative optic sign for uniaxial and biaxial gems using the refractometer, lambda plate, and interference figures. +order: 3.6 +category: fundamentals +difficulty: advanced +icon: prism +related: + - fundamentals/optical-properties + - fundamentals/optical-properties-advanced + - fundamentals/crystal-systems + - equipment/polariscope +tags: + - optic-sign + - interference-figure + - uniaxial + - biaxial + - polariscope + - lambda-plate + +sections: + - title: Principle + content: | + The optic sign is a property of anisotropic gem materials that describes the relationship + between the principal refractive indices: + + - **Uniaxial positive (U+):** the extraordinary ray RI (ε) is greater than the ordinary ray + RI (ω): ε > ω. + - **Uniaxial negative (U−):** ε < ω. + - **Biaxial positive (B+):** the intermediate RI (β) is closer to α (the minimum) than to + γ (the maximum): β − α < γ − β. + - **Biaxial negative (B−):** β is closer to γ: γ − β < β − α. + + The optic sign can be determined by two methods: + 1. **Refractometer rotation** (uniaxial stones only) — observing which shadow edge moves as + the stone is rotated. + 2. **Conoscopic interference figure** with an accessory plate (lambda plate or quartz wedge) + — reading the colour change in the isochromatic rings. + + The interference-figure method uses **Newton's colour series** (the interference colour + sequence seen between crossed polars as retardation increases): yellow → orange → red → + violet → blue → green → yellow (2nd order) …). The lambda plate (530 nm full-wave + retardation plate, "first-order red plate") shifts the retardation by a fixed amount: + addition raises colours toward the next order (blue, 2nd-order tints); subtraction lowers + them (yellow, back toward 1st-order grey). + + *Source: Sturman, B.D., J. Gemmology, 2007. DOI: 10.15506/jog.2007.30.7.443. [VERIFIED]; + Read, P., Gemmology 3rd ed. DOI: 10.4324/9780080507224 [VERIFIED]* + + - title: Uniaxial Procedure — Refractometer Method + content: | + For uniaxial stones with measurable birefringence, the refractometer can be used directly: + + 1. Place the stone table-down on the refractometer hemisphere with contact liquid. + 2. Observe the shadow edge (or edges). A uniaxial stone shows two shadow edges — + the fixed edge (ω, ordinary ray) and the moving edge (ε, extraordinary ray). + 3. Rotate the stone slowly through 360°. The ε edge moves; the ω edge stays fixed. + 4. If the moving edge (ε) is **above** the fixed edge (ω) at maximum separation: + - ε > ω → **Uniaxial positive**. + 5. If the moving edge (ε) is **below** the fixed edge at maximum separation: + - ε < ω → **Uniaxial negative**. + + **Note:** when the stone is oriented with the optic axis perpendicular to the hemisphere + (c-axis pointing up into the contact liquid), both readings coincide as a single shadow + edge at the ω position. Rotate the stone off this orientation to see both edges. + + - title: Uniaxial Procedure — Interference Figure (Lambda Plate) + content: | + The conoscope (convergent polarised light through the polariscope, using a high-powered + condensing lens or the stone itself as a condenser) produces an interference figure for + a stone oriented with its optic axis vertical. + + **Uniaxial optic axis figure:** + - Shows a Maltese cross (isogyre) pattern with concentric isochromatic colour rings. + - The centre of the cross marks the optic axis. + + **Inserting the lambda plate (530 nm first-order red plate):** + + The lambda plate has a defined "slow" direction (the direction of high refractive index, + i.e. the slow vibration direction). When inserted, it adds retardation where the crystal's + slow direction aligns with the plate's slow direction, and subtracts retardation where they + are opposed. + + - In the two quadrants where the crystal's slow ray is parallel to the plate's slow ray: + retardations add → colours **rise** in Newton's series (toward blue, 2nd order). + - In the other two quadrants: retardations subtract → colours **fall** (toward yellow). + + **Reading the sign (principle — without committing to a specific diagram convention):** + + The orientation rule for the plate-in-figure is described in standard optical mineralogy + texts (Read 3rd ed.; Sturman 2007). The key relationship is: in the quadrants where the + crystal's slow ray aligns with the plate slow direction, rising colours indicate the slow + direction of the crystal in that quadrant — from which the sign follows. Consult your + course's specific diagram orientation, as the convention depends on the physical direction + the plate is inserted relative to the polariser/analyser orientation. + + **Practical rule (curriculum-level):** the lambda plate colour shift directly reveals + whether ε or ω is the slow direction: + - If the quadrant showing rising colour corresponds to the ε direction → ε > ω → **positive**. + - If the quadrant showing rising colour corresponds to the ω direction → ε < ω → **negative**. + + A quartz wedge works analogously, showing a series of colour changes as it is inserted, + rather than a single shift. + + callout: + type: warning + title: Diagram Orientation Convention + text: | + The exact labelling of which quadrant (NE/SW vs NW/SE) shows rising or falling colour + depends on the physical orientation of the lambda plate relative to the polariser in your + specific polariscope. Different course textbooks (Read, Kerr, Nesse) may diagram this + with the plate oriented differently. Learn the principle (addition = rising colour in the + slow-slow quadrant) and apply it consistently to your instrument setup. + + - title: Biaxial Procedure — Acute Bisectrix Figure + content: | + For biaxial stones, the acute bisectrix (Bxa) interference figure is used. The stone must + be oriented with the acute bisectrix perpendicular to the polariscope stage — typically + requiring the stone to be oriented by trial and error (or by knowledge of the optic + orientation of the species). + + **Biaxial Bxa figure:** + - Shows two isogyres (hyperbolic curves) that sweep across the field as the stage is rotated. + - The two isogyres curve toward each other; the separation of the two optic axes (2V) is + estimated from the curvature of the isogyres and their angular separation. + + **Inserting the lambda plate:** + - Observe the colour of the isochromatic rings in the concave region between the two + isogyres (facing toward the acute bisectrix). + - **Rising colour (blue)** in the concave region between the isogyres → **biaxial positive**. + - **Falling colour (yellow)** in the concave region → **biaxial negative**. + + This method follows from the same addition/subtraction principle as the uniaxial case, + applied to the orientation of the optic plane. + + *Source: Sturman 2007, DOI: 10.15506/jog.2007.30.7.443 [VERIFIED]* + + - title: Worked Examples by Species + table: + caption: Optic sign for common gem species + headers: + - Gemstone + - Sign + - RI values (ε, ω or α, β, γ) + - Diagnostic note + rows: + - ["Quartz", "U+", "ε 1.553, ω 1.544", "Classic uniaxial positive; interference figure readily obtained"] + - ["Calcite", "U−", "ε 1.486, ω 1.658", "Extreme case; very large birefringence 0.172; ε is the minimum RI"] + - ["Tourmaline", "U−", "ε < ω; RI 1.62–1.65", "Strong pleochroism confirms uniaxial; negative sign"] + - ["Zircon (high)", "U+", "ε up to 1.99, ω 1.78", "High birefringence (0.059) makes figure difficult; sign positive"] + - ["Beryl (aquamarine, emerald)", "U−", "ε < ω; RI 1.56–1.60", "Uniaxial negative; low birefringence 0.003–0.010"] + - ["Corundum (ruby, sapphire)", "U−", "ε 1.760, ω 1.768", "Low birefringence 0.008–0.009; uniaxial negative"] + - ["Apatite", "U−", "RI 1.63–1.64; birefringence 0.002–0.006", "Uniaxial negative; very low birefringence"] + - ["Topaz", "B+", "α 1.609–1.629, β closer to α, γ 1.616–1.637", "Biaxial positive"] + - ["Peridot", "B+ or B−", "α 1.654, β, γ 1.690", "May appear B+/−; biaxial; large birefringence 0.036"] + - ["Chrysoberyl", "B+", "α 1.746, β, γ 1.763", "Biaxial positive; birefringence 0.008–0.010"] + + - title: Common Pitfalls + content: | + Several situations complicate optic sign determination in practice: + + - **Wrong orientation:** if the stone is not oriented with the optic axis (uniaxial) or + acute bisectrix (biaxial) sufficiently close to vertical, an off-centre figure results, + making colour interpretation unreliable. + - **High birefringence:** very high birefringence (e.g. zircon 0.059, calcite 0.172) compresses + the isochromatic rings to tiny concentric circles near the melatope; the lambda plate effect + is harder to read. Thinner sections (or smaller stones) help. + - **Low birefringence:** very low birefringence (e.g. apatite 0.002–0.006) produces very few + or no isochromatic rings — the figure shows only the isogyre cross against a near-uniform + background. The lambda plate still produces a colour shift in the quadrants; read the shift + in the area immediately around the melatope. + - **Dauphiné twinning in quartz:** sector-by-sector anomalous extinction can mimic biaxial + behaviour. Check birefringence (quartz 0.009 is consistent) and look for the sector pattern. + - **Anomalous double refraction (ADR):** cubic (isotropic) stones that have been strained + may show anomalous birefringence under the polariscope. They do not have a true optic sign. + Spinels commonly show ADR (mottled or patchy extinction) rather than a true interference + figure. + + callout: + type: info + title: ADR vs True Birefringence + text: | + If a stone shows irregular "snakeskin" or mottled extinction under crossed polars, suspect + anomalous double refraction (ADR) in a nominally isotropic species (spinel, glass, garnet) + rather than a true biaxial or uniaxial character. A centred interference figure with clear + isogyres is needed before assigning an optic sign. + + - title: Sources + content: | + - Sturman, B.D. "Determination of the optic axial angle in biaxial gemstones and its use + in gemmology." *Journal of Gemmology*, 30(7), 2007, pp. 443–452. + DOI: 10.15506/jog.2007.30.7.443. [VERIFIED] + - Read, P. *Gemmology*, 3rd ed. Routledge, 2012. DOI: 10.4324/9780080507224. [VERIFIED] + - Gem-A Diploma syllabus §3.2: "Optic sign determination from interference figures"; + §4.1: "Optic sign from refractometer rotation." diff --git a/docs/learn/fundamentals/physical-properties.yaml b/docs/learn/fundamentals/physical-properties.yaml index 48119a6..45ba776 100644 --- a/docs/learn/fundamentals/physical-properties.yaml +++ b/docs/learn/fundamentals/physical-properties.yaml @@ -341,6 +341,210 @@ sections: Most synthetic moissanite (SiC) is an electrical semiconductor, while natural diamond (except rare Type IIb blue) is an insulator. + - title: Tenacity — Resistance to Mechanical Deformation + content: | + Tenacity describes how a mineral resists breaking, bending, or deformation. It is distinct + from hardness (resistance to scratching) and from cleavage (the mode of fracture). The + principal tenacity terms used in gemmology are: + + - **Brittle:** fractures without plastic deformation; shatter on impact or under stress. + The fracture surface is conchoidal, uneven, or hackly. Essentially all silicates and + oxides in common gemmology are brittle. + - **Tough:** high resistance to fracture despite lower hardness than brittle gems; typically + an interlocking aggregate structure disperses crack energy. Nephrite and jadeite are the + gemmological standards. + - **Sectile:** can be cut with a knife into shavings without crumbling; deforms plastically + under a sharp edge. Not common in gem minerals; talc (H1) is sectile. + - **Malleable:** can be hammered into thin sheets without crumbling. Metals only — native + gold inclusions in quartz are malleable. + - **Ductile:** can be drawn into a wire. Native gold, platinum. Not a gemmological property + of the gem minerals themselves. + - **Flexible:** thin plates or sheets can be bent without breaking but do not return to + shape (plastic deformation). Talc, chlorite, gypsum selenite plates. + - **Elastic:** thin plates can be bent and spring back to original shape without permanent + deformation. Distinguishes muscovite mica (elastic) from chlorite (flexible but not elastic). + + *Source: Read, Gemmology 3rd ed. DOI: 10.4324/9780080507224 [VERIFIED]* + subsections: + - title: Tenacity in gem identification + table: + caption: Tenacity terms with gem examples + headers: + - Tenacity + - Gem/mineral examples + - Diagnostic application + rows: + - ["Brittle", "Diamond, corundum, quartz, tourmaline, topaz, garnet, spinel", "Most faceted gems; conchoidal or uneven fracture surface"] + - ["Tough", "Nephrite (H 6–6.5), jadeite (H 6.5–7)", "Nephrite tougher than diamond despite lower hardness — fibrous interlocking structure"] + - ["Sectile", "Amber (slightly under knife), talc", "Amber can be shaved; relevant in amber vs plastic vs copal testing"] + - ["Malleable", "Native gold (inclusion in quartz)", "Gold leaf inclusions spread under pressure"] + - ["Flexible (not elastic)", "Talc, chlorite, gypsum selenite", "Chlorite inclusions in gems flex under probe but do not spring back"] + - ["Elastic", "Muscovite, phlogopite mica", "Mica inclusions spring back when probe is removed — distinguishes from chlorite"] + + - title: Toughness vs hardness + content: | + The toughness/hardness distinction is examinable at Diploma level: + + - **Hardness** = resistance to scratching (Mohs scale, a surface property). + - **Toughness** = resistance to fracture (a bulk property of the interlocked structure). + + Nephrite jade (H 6–6.5) is tougher than diamond (H 10) because its densely interlocking + fibrous tremolite–actinolite structure prevents crack propagation. Diamond, despite maximum + hardness, has perfect octahedral cleavage and brittle tenacity — a sharp blow in the {111} + direction will cleave it. + + - title: Magnetism in Gems + content: | + Gem minerals may be diamagnetic, paramagnetic, or ferromagnetic/ferrimagnetic. A strong N52 + neodymium magnet provides a rapid, non-destructive field test that correlates with + iron (Fe) and manganese (Mn) content. + + **Magnetic behaviour types:** + - **Diamagnetic:** all materials without unpaired electrons have a very weak repulsive + response to a magnetic field. Most gem silicates with no transition metal are effectively + diamagnetic (quartz, topaz, diamond, spinel). + - **Paramagnetic:** materials with unpaired electrons in the 3d shell are weakly attracted. + Susceptibility follows the Curie law (χ ∝ 1/T). Fe²⁺ (4 unpaired electrons), Fe³⁺ + (5 unpaired), Mn²⁺ (5 unpaired), Cr³⁺ (3 unpaired) all contribute. Gems with high Fe + or Mn content are detectably paramagnetic with a strong N52 magnet. + - **Ferrimagnetic:** exchange-coupled spins; found in iron oxide inclusions (magnetite + Fe₃O₄) rather than in gem silicates themselves. A stone with sufficient magnetite + inclusions can be attracted even if the host is diamagnetic. + + *Source: Hoover, Williams, Williams & Mitchell, J. Gemmology, 2008. + DOI: 10.15506/jog.2008.31.3.91 [VERIFIED]; Hoover, Gems & Gemology, 2011. + DOI: 10.5741/gems.47.4.272 [VERIFIED]* + subsections: + - title: Gem species magnetic response + table: + caption: Magnetic response of common gem species to N52 neodymium magnet + headers: + - Gem species + - Response + - Reason + rows: + - ["Almandine garnet (Fe-rich)", "Strongly attracted", "High Fe²⁺/Fe³⁺; largest susceptibility among garnets"] + - ["Spessartine garnet (Mn-rich)", "Attracted", "Mn²⁺ (5 unpaired electrons); varies with Mn content"] + - ["Demantoid garnet (andradite, Fe³⁺)", "Attracted", "Paramagnetic from Fe³⁺; useful vs green tourmaline"] + - ["Tsavorite (grossular with V, Cr)", "Weakly attracted", "Cr and V paramagnetic; weaker than almandine"] + - ["Pyrope (pure end-member)", "Very weakly attracted or diamagnetic", "Low Fe, low Mn; rhodolite (pyrope-almandine) intermediate"] + - ["Peridot (Fe²⁺ in olivine)", "Attracted", "Fe²⁺ essential; separable from green tourmaline or green sapphire"] + - ["Blue/indicolite tourmaline (Fe-bearing)", "Weakly attracted", "Fe-bearing but weaker response than Fe-rich garnets"] + - ["Fe-bearing sapphire", "Weakly attracted", "Fe paramagnetic; less than garnets"] + - ["Diamond, quartz, spinel, topaz", "No response (diamagnetic)", "No unpaired d-electrons in pure form"] + - ["Magnetite inclusions (in star sapphire, star diopside etc.)", "Strongly attracted", "Ferrimagnetic Fe₃O₄; even if host is diamagnetic"] + + - title: Diagnostic applications + content: | + - **Rapid field separation:** a N52 magnet separates almandine, spessartine, and demantoid + from diamagnetic simulants (glass, CZ) without instruments. + - **Garnet composition:** Hoover (2008, 2011) demonstrated that magnetic susceptibility + measurement can resolve garnet species and compositions more precisely than RI alone, + especially for mixed-composition stones in the almandine–pyrope–spessartine series. + - **Above-refractometer garnets:** demantoid RI (~1.89) exceeds the standard refractometer + range (~1.79). The magnet test complements by confirming the garnet identification. + - **Safety note:** N52 neodymium magnets are extremely strong; handle with care around + electronic equipment, credit cards, and polishing compounds. + + - title: Brewster's Angle and Reflection Polarisation + content: | + Brewster's angle (θ_B) is the angle of incidence at which light reflected from a polished + gem surface becomes completely plane-polarised. At this angle, the reflected and refracted + rays are perpendicular to each other. + + **Formula:** tan(θ_B) = n (for air/gem interface, n₁ = 1, n₂ = n of gem) + + **Derivation:** At Brewster's angle, the reflected and refracted beams are at 90°. By Snell's + law: n₁ sin(θ_B) = n₂ sin(90° − θ_B) = n₂ cos(θ_B), giving tan(θ_B) = n₂/n₁ = n. + + **Worked example — diamond:** + n(diamond) = 2.417; θ_B = arctan(2.417) = approximately 67.5°. + At this angle, light reflected from the diamond surface vibrates only in the plane + perpendicular to the plane of incidence — fully polarised. + + A polaroid filter held at the appropriate angle above a gem surface eliminates surface + glare at Brewster's angle, improving transparency during examination. The immersion method + in the polariscope similarly exploits this suppression of surface reflections. + + *Source: Read, P.G. "An Experimental Brewster-Angle Refractometer." J. Gemmology, 1979. + DOI: 10.15506/jog.1979.16.8.537 [VERIFIED]; Read, P. "Further development of the + Brewster-angle refractometer." J. Gemmology, 1988. DOI: 10.15506/jog.1988.21.1.36 [VERIFIED]* + subsections: + - title: Brewster angle reference values + content: | + The values below are calculated from the formula θ_B = arctan(n) using the known RI + of each gem material. Brewster's angle increases with RI — higher-RI stones require a + steeper angle of incidence to achieve full polarisation of the reflected beam. + table: + caption: Brewster angle calculated from RI (formula confirmed; individual RI values from Read 3rd ed.) + headers: + - Gem + - RI (n, mean or single value) + - Brewster angle (arctan n) + rows: + - ["Fluorite", "1.434", "~55.1°"] + - ["Quartz", "1.548 (mean)", "~57.1°"] + - ["Sapphire/corundum", "1.770 (mean)", "~60.6°"] + - ["Zircon (high)", "~1.92 (mean)", "~62.4°"] + - ["CZ (cubic zirconia)", "~2.17", "~65.2°"] + - ["Diamond", "2.417", "~67.5°"] + + - title: Brewster-angle refractometer + content: | + Peter Read developed an experimental Brewster-angle refractometer (1979, 1988) that + extends RI measurement beyond the standard contact-liquid refractometer limit of ~1.79 + by detecting the angle at which reflected light becomes fully polarised. This allows + measurement of high-RI stones such as diamond (2.417), CZ (2.17), and high zircon + (up to 1.99). + + - title: Dispersion — Named Values (B–G Interval) + content: | + Dispersion in gemmology is measured as the difference in refractive index between the + Fraunhofer B line (686.7 nm, red) and the G line (430.8 nm, violet): + + **Dispersion = n(G) − n(B)** + + A high dispersion means white light is strongly separated into spectral colours ("fire") + when internally reflected and refracted. Fire is visible to the eye only in stones with + dispersion > ~0.025 under ideal conditions. + + High dispersion correlates with: (a) high mean RI, (b) proximity of strong absorption + bands to the visible range (steepening the dispersion curve). + + *Source: Read, Gemmology 3rd ed. DOI: 10.4324/9780080507224 [VERIFIED]; + Nassau, Physics and Chemistry of Color, 2001, pp. 52–56 [VERIFIED]* + table: + caption: Dispersion (B–G interval) for gem materials — CZ value is 0.060 (Read 7th; VERIFIED; NOT 0.065) + headers: + - Material + - Dispersion (B–G) + - Fire quality / notes + rows: + - ["Rutile (TiO₂ synthetic)", "0.280", "Extreme; rarely faceted due to very high birefringence"] + - ["Strontium titanate (SrTiO₃)", "0.190", "Synthetic; formerly 'fabulite'; highest of gem simulants"] + - ["Synthetic moissanite (SiC)", "0.104", "Higher than diamond; noticeable fire in faceted stones"] + - ["Cubic zirconia (ZrO₂)", "0.060", "Higher than diamond; conspicuous fire — diagnostic vs. diamond (Read 3rd ed. confirmed)"] + - ["Sphene / titanite", "0.051", "Very high; 'adamantine to sub-adamantine' fire; visible coloured flashes"] + - ["Demantoid garnet", "0.057", "Highest of natural garnets; visible fire even through green bodycolour"] + - ["GGG (gadolinium gallium garnet)", "0.045", "Synthetic diamond simulant"] + - ["Diamond", "0.044", "Benchmark for comparison; high fire by natural gem standards"] + - ["Zircon", "0.039", "High; noticeable fire; high birefringence also contributes to scintillation"] + - ["YAG (yttrium aluminium garnet)", "0.028", "Synthetic; moderate fire"] + - ["Almandine garnet", "0.027", "Moderate; noticeable in bright lighting"] + - ["Spinel", "0.020", "Moderate"] + - ["Corundum (ruby, sapphire)", "0.018", "Low; fire rarely visible in coloured stones"] + - ["Glass (typical)", "0.010–0.020", "Varies widely with composition and heavy-metal content"] + - ["Quartz", "0.013", "Low"] + - ["Fluorite", "0.007", "Very low; 'dead' appearance despite sometimes vivid colour"] + + callout: + type: warning + title: CZ Dispersion — Confirmed Value + text: | + Cubic zirconia dispersion = **0.060** (Read, Gemmology 3rd ed.; DOI-verified source). + A figure of 0.065 sometimes appears in trade literature but is unverified by a peer-reviewed + source and should not be used. The canonical gemmological value is 0.060. + - title: Practice with Interactive Tools callout: type: tip diff --git a/docs/learn/fundamentals/twin-laws.yaml b/docs/learn/fundamentals/twin-laws.yaml new file mode 100644 index 0000000..6f56363 --- /dev/null +++ b/docs/learn/fundamentals/twin-laws.yaml @@ -0,0 +1,256 @@ +title: Twin Laws in Gemmology +description: Named twin laws — spinel, Carlsbad, Manebach, Baveno, albite, pericline, Brazil, Dauphiné, Japan — and corundum parting, with diagnostic applications. +order: 1.6 +category: fundamentals +difficulty: advanced +icon: gem +related: + - fundamentals/crystal-systems + - fundamentals/crystallography-advanced + - fundamentals/physical-properties +tags: + - twinning + - twin-laws + - crystallography + - parting + - identification + +sections: + - title: What is Twinning? + content: | + A crystal twin is an intergrowth of two or more crystal individuals of the same species that + share some lattice points but have different crystallographic orientations. The geometric + relationship between the parts is defined by the **twin law** — a symmetry operation + (reflection across a twin plane, or rotation about a twin axis) that is not a symmetry + element of the point group of the untwinned crystal. + + **Types of twin by geometry:** + - **Contact twin:** individuals joined at a flat, planar composition surface (the twin plane). + The boundary is visible as a straight line on the crystal face. + - **Penetration twin:** individuals interpenetrate; no single planar boundary. The composition + surface is irregular or concave. + - **Polysynthetic (lamellar) twin:** repeated alternating thin lamellae, each related by the + same twin law. Produces parallel striations on crystal faces or cleavage surfaces. + - **Cyclic twin:** more than two individuals, each related by the same twin operation, arranged + around a common axis; may produce cross-, star-, or ring-shaped habits. + + The twin plane or axis is described in Miller index notation of the host crystal system. + + *Source: Read, P. Gemmology, 3rd ed. DOI: 10.4324/9780080507224 [VERIFIED]* + + - title: Spinel Law — Cubic {111} + content: | + The spinel law is the defining twin law of the cubic system, operating on the {111} octahedral + planes. + + - **System:** Cubic + - **Twin element:** {111} twin plane + - **Type:** Contact twin (occasionally polysynthetic as "contact polysynthetic") + - **Recognition feature:** Produces flat, triangular "macle" — an octahedron that appears + compressed perpendicular to the {111} plane. The contact face shows a re-entrant notch + (triangular depression) where the two individuals meet at the composition surface. + - **Gem species:** + - **Spinel:** flat triangular octahedra ("spinels" in the geological sense); the macle habit + is diagnostic for rough spinel in alluvial deposits. + - **Diamond:** flat triangular macles ("macle diamonds"), characteristic of some alluvial + diamond rough. The triangular table and re-entrant notch are recognisable sight-holder + features. + + callout: + type: info + title: Macle — FGA Terminology + text: | + "Macle" (from French) is the traditional term for a contact twin on the spinel law — a flat, + triangular crystal that looks like two octahedra compressed along {111}. The term is used + in FGA examination contexts for both spinel and diamond. + + - title: Carlsbad, Manebach, and Baveno Laws — Monoclinic Feldspars + content: | + Three named twin laws apply to monoclinic feldspars (orthoclase, sanidine), distinguished + by their twin element and the geometry of the resulting composition surface. + subsections: + - title: Carlsbad law + content: | + - **System:** Monoclinic + - **Twin element:** c-axis ([001]) as twin axis — a penetration twin + - **Type:** Penetration twin + - **Recognition:** Two individuals interpenetrate; the composition surface is irregular + and oblique to the long axis of the crystal. Produces a characteristic elongated + crystal with an irregular diagonal composition surface visible on the prism face. + The two halves of the crystal may show slightly different colours or lustre. + - **Gem species:** Orthoclase feldspar (moonstone), sanidine. + + - title: Manebach law + content: | + - **System:** Monoclinic + - **Twin element:** {001} pinacoidal twin plane — contact twin + - **Type:** Contact twin + - **Recognition:** The {001} pinacoidal cleavage face of orthoclase is also the + composition surface. The twin appears as a book-like intergrowth where the cleavage + and the twin boundary coincide. Less commonly encountered than Carlsbad. + - **Gem species:** Orthoclase. + + - title: Baveno law + content: | + - **System:** Monoclinic + - **Twin element:** {021} twin plane — contact twin + - **Type:** Contact twin + - **Recognition:** The {021} face produces a re-entrant notch (triangular depression) at + the junction of the two individuals. The Baveno law produces a triangular re-entrant + angle on the crystal face, distinguishing it from Carlsbad. + - **Gem species:** Orthoclase. Also known to occur in some plagioclase. + + - title: Albite and Pericline Laws — Triclinic Plagioclase + content: | + Plagioclase feldspars (albite, oligoclase, labradorite, bytownite, anorthite) are triclinic + and characteristically show two simultaneous polysynthetic twin laws that produce the + diagnostic striations used to distinguish plagioclase from orthoclase. + subsections: + - title: Albite law + content: | + - **System:** Triclinic + - **Twin element:** {010} twin plane — polysynthetic contact + - **Type:** Polysynthetic (lamellar) contact twin + - **Recognition:** Produces fine parallel striations running across the {001} cleavage + face of plagioclase. The striations are perpendicular to the cleavage step edges and + are gemmologically diagnostic: plagioclase feldspars show these striations; orthoclase + does not. Visible under a loupe (10×) as fine parallel lines on the cleavage surface. + - **Gem species:** Labradorite, sunstone, albite, oligoclase (all plagioclase). + + - title: Pericline law + content: | + - **System:** Triclinic + - **Twin element:** b-axis (the "rhombic section") — polysynthetic penetration + - **Type:** Polysynthetic penetration twin + - **Recognition:** Produces striations on the {010} face at right angles to the + albite-law striations. Both laws operate simultaneously in plagioclase, giving a + grid-like pattern at the microscopic scale. The pericline striations are parallel to + the cleavage traces on the {010} pinacoid. + - **Gem species:** Labradorite, albite; typically co-occurs with albite law. + + callout: + type: tip + title: Diagnostic Test — Plagioclase vs. Orthoclase + text: | + Albite-law polysynthetic twinning striations on the {001} cleavage face reliably + distinguish plagioclase (striations present) from orthoclase (no striations) without + instruments. Use 10× loupe under oblique illumination to see the fine parallel lines. + + - title: Brazil Law — Trigonal Quartz (Left/Right Sectors) + content: | + - **System:** Trigonal + - **Twin element:** {11̄20} twin plane — polysynthetic penetration twin + - **Type:** Polysynthetic penetration twin + - **Recognition:** Sectors of opposite optical handedness (left-handed and right-handed + quartz) are intergrown within a single crystal. There is no external morphological + distinction between the two sectors — the twin is invisible optically by normal + transmitted light. Detection requires: + - **Etch figures:** acid etching of the r-face produces triangular etch pits of opposite + orientation in left- vs. right-handed sectors. + - **X-ray diffraction:** Laue photographs show the handedness. + - **Effect on properties:** Brazil-law twins cancel piezoelectric response in alternating + sectors. This is why natural quartz must be checked for Brazil twinning before use in + precision frequency applications; only single-handed quartz is useful. Gem-quality natural + quartz for piezoelectric use must be twin-free. + - **Gem species:** All varieties of quartz (amethyst, citrine, rock crystal, smoky quartz). + + - title: Dauphiné Law — Trigonal Quartz (Electrical Twin) + content: | + - **System:** Trigonal + - **Twin element:** c-axis (rotation of 60° or 180°) — penetration twin + - **Type:** Penetration twin + - **Recognition:** Dauphiné-law twins are crystallographically rotated by 60° about the + c-axis, but this operation is equivalent to a 180° rotation in the point group 32 (the + quartz class). They are **indistinguishable externally**: no striations, no colour + difference, and no change in RI or birefringence. + - Under the polariscope, Dauphiné twinning causes sector-by-sector anomalous extinction + — different sectors extinguish at slightly different angles, producing an irregular + "flashing" pattern under crossed polars. This can confuse the gemmologist if not + recognised. + - The twin does NOT change the optical handedness of the quartz (unlike Brazil law), + so it has no effect on optical rotation. + - **Electrical twin:** Dauphiné twinning reverses the direction of the a-axes. In sectors + separated by the twin, the piezoelectric polarity is reversed. This is the origin of the + term "electrical twin." + - **Gem species:** Quartz (common; many quartz crystals contain Dauphiné domains). + + - title: Japan Law — Quartz Heart-Shaped Twin + content: | + - **System:** Trigonal + - **Twin element:** {11̄22} twin plane — contact twin + - **Type:** Contact twin + - **Recognition:** Produces a heart-shaped or V-shaped contact twin. The two prism faces of + the two individuals meet at a re-entrant angle of approximately 84°, giving the + characteristic heart ("macle") shape. The composition surface is a flat plane coinciding + with the {11̄22} face. + - **Named for:** Specimens from Yamanashi prefecture, Japan, where this twin habit is + particularly well developed. Also found in Brazilian and Alpine quartz. + - **Gem species:** Quartz. + + - title: Corundum Twinning and Parting + content: | + Corundum (ruby and sapphire) has no true cleavage. Instead, it commonly shows parting on + two planes that arise from polysynthetic twinning on those planes. This is a classic + examination trap: the Diploma requires candidates to know that corundum has **no cleavage**, + only parting. + + **Twin plane:** {10-11} (rhombohedral plane, trigonal four-index notation). + + Repeated polysynthetic twinning on {10-11} produces closely spaced lamellae of alternating + orientation. The composition planes between twin individuals are slightly weaker than the + bulk crystal, producing the {10-11} parting. + + Additionally, corundum shows {0001} basal parting (c-parting) from polysynthetic twinning + on the basal pinacoid plane. + + *Source: Pignatelli, Nespolo & Pardieu, Mineralogy and Petrology, 2024. + DOI: 10.1007/s00710-024-00858-1 [VERIFIED]* + subsections: + - title: Recognition of corundum parting + content: | + On broken corundum rough, parting appears as a series of parallel flat steps (not a + smooth conchoidal fracture curve) at a consistent angle — the {10-11} or {0001} plane. + In faceted stones, parting planes appear as reflective internal planes, sometimes showing + interference colour (iridescence), and can be mistaken for cleavage cracks. + + The {10-11} parting is exploited in oriented cutting of corundum rough: + - Cutters can split rough along the parting to orient the table perpendicular to the c-axis. + - This exploits the parting as a controlled guide plane. + + - title: Parting vs cleavage — examination point + table: + headers: + - Feature + - Cleavage + - Parting + rows: + - ["Cause", "Weak bonding along crystallographic planes inherent to structure", "Twinning lamellae or exsolution planes (not inherent)"] + - ["Universality", "Present in all crystals of the species", "Only in crystals that are twinned or have undergone exsolution"] + - ["Corundum", "NONE", "Yes — {10-11} and {0001}"] + - ["Topaz", "{001} perfect cleavage", "Not significant"] + - ["Diamond", "{111} perfect octahedral cleavage", "Not significant"] + + - title: Diagnostic Relevance + content: | + Named twin laws appear at multiple points in gemmological identification: + + - **Spinel macle / diamond macle:** sight-holder feature for alluvial rough; flat triangular + habit with re-entrant notch is immediately recognisable. + - **Albite striations on plagioclase cleavage:** fastest loupe test to distinguish plagioclase + from orthoclase without instruments; decisive when RI values overlap. + - **Dauphiné twinning in quartz:** explains anomalous extinction patterns under the polariscope; + without this knowledge a gemmologist might mistake the stone for biaxial. + - **Brazil twinning:** explains why some quartz shows alternating optical effects; relevant + when evaluating quartz for piezoelectric use. + - **Corundum parting vs cleavage:** stating "corundum has perfect basal cleavage" is a + Diploma-level examination error. The correct answer is parting along {0001} and {10-11}. + - **Labradorescence:** the polysynthetic albite and pericline twinning lamellae in labradorite + create the thin-film interference responsible for labradorescence — twinning is directly + linked to the phenomenon. + + - title: Sources + content: | + - Read, P. *Gemmology*, 3rd ed. Routledge, 2012. DOI: 10.4324/9780080507224. [VERIFIED] + - Pignatelli, I.; Nespolo, M.; Pardieu, V. et al. "Basal twinning of Greenland corundum." + *Mineralogy and Petrology*, 2024. DOI: 10.1007/s00710-024-00858-1. [VERIFIED] + - Gem-A Diploma syllabus §3.1: twinning types and named twin laws. diff --git a/docs/learn/identification/treatments-deep/beryllium-diffusion.yaml b/docs/learn/identification/treatments-deep/beryllium-diffusion.yaml new file mode 100644 index 0000000..d7a52f3 --- /dev/null +++ b/docs/learn/identification/treatments-deep/beryllium-diffusion.yaml @@ -0,0 +1,95 @@ +title: Beryllium Diffusion — Deep Diagnostic Reference +description: Full per-method detection protocol for beryllium lattice diffusion in corundum, with disclosure standards and stability data. +order: 1 +category: identification +difficulty: advanced +icon: beaker +related: + - identification/treatments + - identification/inclusions + - species/corundum +tags: + - beryllium-diffusion + - sapphire + - diffusion + - LA-ICP-MS + - SIMS + +sections: + - title: Process and Conditions + content: | + Rough sapphire is packed in beryllium-bearing powder (chrysoberyl or synthetic BeO) + and fired at **1700–1800 °C** in an oxidising atmosphere for 12–100 hours. + + Be²⁺ ions (ionic radius 0.27 Å) are small enough to diffuse through the corundum + lattice — unlike Ti or Cr, which remain near-surface. They act as charge compensators + enabling trapped-hole colour centres (h-Fe: iron paired with oxygen vacancies), + producing strong orange/yellow absorption throughout the stone. + + The Songea (Tanzania) case study (from 2001 onward) demonstrated that ordinary sapphire + could be transformed into commercially intense padparadscha-like material unachievable + by plain heat treatment. + + Be²⁺ diffuses into corundum at processing temperatures by creating charge-compensated + trapped-hole chromophores responsible for the yellow-orange coloration (Emmett et al. 2003). + Diffusion of beryllium into various types of sapphire can shift their chemistry from + donor- to acceptor-dominated, forming the hole chromophore (Emmett et al. 2023). + + callout: + type: warning + title: Cannot Be Detected by Standard Tools + text: | + Beryllium diffusion cannot be reliably detected by standard gem-testing instruments + (loupe, refractometer, UV lamp, spectroscope). LA-ICP-MS or SIMS is required for a + definitive result. Immersion microscopy provides indicative signs only. + + - title: Detection — Full Protocol (Loupe to SIMS) + table: + caption: Detection Sequence — Beryllium Diffusion (simplest to most advanced) + headers: + - Method + - Finding + - Reliability + - Notes + rows: + - ["10× loupe / naked eye", "Colour may appear suspiciously homogeneous and intense for the origin; padparadscha oranges from Sri Lanka rarely achieve this saturation naturally", "Indicative only", "Cannot distinguish from plain heat"] + - ["Immersion microscope (40×, dark-field, di-iodomethane)", "In poorly-treated or small stones: slight colour concentration at facet junctions ('spider-web' faint); less pronounced than Ti surface diffusion because penetration is deeper; may appear where facets approach the girdle", "Suggestive — not conclusive", "More reliable for Ti surface diffusion; less reliable for Be"] + - ["Chelsea Colour Filter", "No specific diagnostic reaction", "Not useful", "Skip in workflow"] + - ["UV fluorescence (LWUV/SWUV)", "No reliable discrimination on its own", "Not useful", "Skip in workflow"] + - ["LA-ICP-MS (Laser Ablation ICP-MS)", "Be >1–2 ppm in orange/yellow corundum is diagnostic; natural corundum contains <0.1 ppm Be", "Definitive", "Industry standard for lab detection; Emmett et al. 2003 establishes ppm threshold"] + - ["SIMS (Secondary Ion Mass Spectrometry)", "Concentration profile from surface to interior; diffusion gradient (high at surface, declining inward) confirms treatment; flat low profile confirms natural", "Gold standard", "Highest sensitivity (~ppb); maps the Be gradient unambiguously"] + - ["LIBS (Laser-Induced Breakdown Spectroscopy)", "Detects Be semi-quantitatively; semi-destructive; less precise than LA-ICP-MS", "Supportive", "Occasionally used in trade; not preferred for definitive reports"] + + - title: Effect on the Gem + content: | + - Colour is **lattice-deep**: re-cutting does not remove it (distinguish from Ti surface diffusion) + - Produces intense orange, yellow, or padparadscha (orange-pink) colours throughout the stone + - Some colour zoning may persist if natural chemistry was uneven + - Ruby subjected to Be diffusion can show reddening or colour improvement in marginally red stones + + - title: Disclosure Standards + content: | + - **CIBJO / AGTA**: must be disclosed as a treatment; AGTA code "U" (diffusion) + - **GIA**: reports "lattice diffusion treatment — beryllium present"; NOT acceptable + to describe the stone simply as "heated" + - **LMHC**: classified as a treatment requiring specific disclosure separate from + plain heat treatment (H); coded H(b) or H(Be) on many laboratory reports + - **Gem-A**: students must understand that Be-diffusion is a fundamentally different + treatment from plain heating and requires a separate disclosure statement + + - title: Stability + content: | + - **Permanent** under normal wearing conditions; lattice-level diffusion is not + reversible by light, heat, or solvents + - Re-polishing does NOT remove colour (distinguish from Ti surface diffusion) + - Ultrasonic and steam cleaning: safe + - The treatment itself is stable but does not affect overall corundum durability (Mohs 9) + + - title: Sources + content: | + - Emmett, J.L. et al. 2003. Beryllium Diffusion of Ruby and Sapphire. *Gems & Gemology*. + DOI: 10.5741/gems.39.2.84 [VERIFIED — live Crossref API confirmed] + - Emmett, J.L. et al. 2023. Yellow Sapphire: Natural, Heat-Treated, Beryllium-Diffused, + and Synthetic. *Gems & Gemology*. DOI: 10.5741/gems.59.3.268 [VERIFIED] + - McClure, S.F. et al. 2010. Gemstone Enhancement and Its Detection in the 2000s. + *Gems & Gemology*. DOI: 10.5741/gems.46.3.218 [VERIFIED] diff --git a/docs/learn/identification/treatments-deep/cvd-diamond.yaml b/docs/learn/identification/treatments-deep/cvd-diamond.yaml new file mode 100644 index 0000000..623da6d --- /dev/null +++ b/docs/learn/identification/treatments-deep/cvd-diamond.yaml @@ -0,0 +1,125 @@ +title: CVD Diamond Detection — Deep Diagnostic Reference +description: Full detection protocol for CVD synthetic diamonds, distinguishing from natural and HPHT-treated stones using DiamondView, FTIR, and photoluminescence. +order: 4 +category: identification +difficulty: advanced +icon: diamond +related: + - identification/treatments + - identification/synthetics + - species/diamond +tags: + - CVD + - synthetic-diamond + - DiamondView + - SiV-centre + - photoluminescence + +sections: + - title: CVD Growth Process + content: | + Chemical Vapour Deposition (CVD) grows diamond from a carbon-bearing gas plasma + (typically CH₄/H₂) at low pressure (~100 torr) and ~700–1000 °C substrate temperature. + Growth proceeds in columnar layers (step-flow mechanism), producing a characteristic + striated internal structure. + + CVD diamonds are typically Type IIa (near-nitrogen-free as grown) and colourless to + light brown. They may undergo a secondary HPHT annealing step to remove residual brown + colour, which can suppress some CVD markers and complicate detection. + + Single-crystal CVD synthetic diamond is clearly distinguishable from natural diamond by + absorption, photoluminescence, and cathodoluminescence spectra showing impurity-related + features not seen in natural diamonds (Martineau et al. 2004). + + DiamondView indicates strong luminescence at 637 nm (NV⁻ centre) with orange-red + phosphorescence accompanied by striations due to step-flow growth (threads and bundles + on the surface) (Zhang et al. 2024). + callout: + type: info + title: F-03 Flag Resolved + text: | + The orange-red phosphorescence of CVD diamond under DiamondView (SW UV 225 nm) is + now documented in Zhang et al. 2024 (10.3390/cryst14090804, [VERIFIED]). This citation + resolves the VERIFIED.md flag (F-03 / Conflict 5) that previously lacked a primary + peer-reviewed source. Use this as the definitive citation for this diagnostic claim. + + - title: Key CVD Growth Features + table: + caption: CVD Diamond — Characteristic Diagnostic Features + headers: + - Feature + - Description + - Origin + rows: + - ["SiV⁻ doublet at 736.9/736.6 nm (PL)", "Silicon-vacancy centre from Si contamination in growth chamber; seen in PL at 77 K", "Growth artifact — trace Si in plasma"] + - ["Columnar/striated growth pattern (DiamondView)", "Threads and bundles perpendicular to growth direction; step-flow mechanism produces layered striae", "CVD layer growth architecture"] + - ["Orange-red phosphorescence (DiamondView, 225 nm)", "Characteristic phosphorescence not seen in natural diamond or HPHT synthetics (Zhang et al. 2024)", "NV⁻ related; step-flow growth contribution"] + - ["NV centres NV⁻ (637 nm) / NV⁰ (575 nm)", "Present in most CVD stones; ratio may differ from HPHT-treated natural diamonds", "N-vacancy pairs in Type IIa lattice"] + - ["Type IIa FTIR signature", "No N absorption >5 ppm; NV-H (NVH⁰) at 3123 cm⁻¹ in some samples", "Near-nitrogen-free growth environment"] + - ["Anomalous birefringence", "Uniform or banded strain from columnar growth; distinct from natural plastic deformation patterns", "Growth stress in CVD layers"] + + - title: Detection Methods — Full Protocol + table: + caption: CVD Diamond Detection (simplest to most advanced) + headers: + - Method + - Finding + - Reliability + - Notes + rows: + - ["LWUV fluorescence (365 nm)", "Variable — inert, orange, or blue depending on post-growth HPHT annealing; anomalous uniformity across the stone", "Preliminary screening", "Cannot confirm CVD alone; triggers lab testing"] + - ["SWUV fluorescence", "Often strong and uniform; lacks the sector fluorescence pattern of HPHT natural diamonds", "Indicative", "Supports but does not confirm CVD"] + - ["DiamondView (225 nm SW UV imaging)", "Orange-red phosphorescence (diagnostic when present); columnar/striated growth — no octahedral sectors; distinct from HPHT cross-hatched sectors", "Most diagnostic single test", "Zhang et al. 2024 is the primary reference for the phosphorescence claim"] + - ["FTIR", "Type IIa signature (N <5 ppm); NV-H absorption at 3123 cm⁻¹ in some CVD samples with N doping", "Instrument test", "Distinguishes Type IIa — necessary but not sufficient for CVD identification alone"] + - ["Photoluminescence at 77 K", "SiV⁻ doublet at 736.9/736.6 nm — characteristic of CVD origin; rarely in natural or HPHT-treated stones; NV⁰ (575 nm) and NV⁻ (637 nm) also present", "Gold-standard lab test", "SiV⁻ doublet is the most specific CVD marker in PL"] + - ["UV-Vis absorption", "Type IIa spectrum; possible 270 nm band if N-doped during growth", "Supporting", "Consistent with Type IIa; not CVD-specific"] + + - title: CVD vs HPHT Synthetic vs Natural — Comparison + table: + caption: Diamond Type Comparison for Identification + headers: + - Property + - Natural Type Ia + - Natural Type IIa + - HPHT-Treated Natural IIa + - CVD Synthetic + - HPHT Synthetic + rows: + - ["FTIR N content", ">100 ppm N (aggregated)", "<5 ppm N", "<5 ppm N", "<5 ppm N (as grown)", "Variable N (type Ib to IIa)"] + - ["LWUV fluorescence", "Blue N3 (most stones)", "Weak/inert", "Inert (typical)", "Variable", "Variable"] + - ["DiamondView pattern", "Octahedral growth sectors", "Weak/irregular", "Cross-hatched green sectors", "Columnar/striated threads", "Cuboctahedral sectors"] + - ["DiamondView phosphorescence", "Rare", "Rare", "Variable", "Orange-red (diagnostic)", "Variable"] + - ["PL SiV⁻ 737 nm", "Absent", "Absent", "Absent", "Present (most stones)", "Absent"] + - ["PL NV⁻/NV⁰ ratio", "Varies with type", "Varies", "High NV⁻ (treated)", "High NV⁻", "Varies"] + + - title: Secondary HPHT Complication + content: | + Some CVD diamonds undergo a secondary HPHT step to remove residual brown colour + (a common by-product of CVD growth). This can: + + - Suppress or modify the SiV⁻ centre (reduces reliability of this marker) + - Change the LWUV fluorescence response + - Produce a DiamondView pattern that combines CVD columnar striations with HPHT-like + modification of the fluorescence + + Expert laboratory testing is required when HPHT-annealed CVD is suspected. The columnar + growth architecture is typically still visible in DiamondView even after secondary HPHT. + + - title: Disclosure and Stability + content: | + - **Disclosure**: mandatory as "synthetic diamond" or "laboratory-grown diamond" per all + governing bodies; "cultured" or "cultivated" are not acceptable per CIBJO + - **GIA, Gem-A, SSEF**: do not grade as natural; issue separate synthetic grading reports + with laser-inscribed "LG" notation + - **Stability**: as a diamond, physical and chemical durability is identical to natural; + colour treatment (if HPHT-annealed) is permanent + + - title: Sources + content: | + - Martineau, P.M. et al. 2004. Identification of Synthetic Diamond Grown Using Chemical + Vapor Deposition (CVD). *Gems & Gemology*. DOI: 10.5741/gems.40.1.2 [VERIFIED] + - Zhang, Y.; Shi, G.; Xie, Z. 2024. Spectral Characteristics of Nitrogen-Doped CVD Synthetic + Diamonds and the Origin of Surface Blue Fluorescence. *Crystals*. + DOI: 10.3390/cryst14090804 [VERIFIED] + - Eaton-Magana, S.; Shigley, J.E.; Breeding, C.M. 2017. Observations on HPHT-Grown + Synthetic Diamonds: A Review. *Gems & Gemology*. DOI: 10.5741/gems.53.3.262 [VERIFIED] diff --git a/docs/learn/identification/treatments-deep/hpht-diamond.yaml b/docs/learn/identification/treatments-deep/hpht-diamond.yaml new file mode 100644 index 0000000..ef8816d --- /dev/null +++ b/docs/learn/identification/treatments-deep/hpht-diamond.yaml @@ -0,0 +1,134 @@ +title: HPHT Diamond Treatment — Deep Diagnostic Reference +description: Full detection protocol for HPHT-treated natural diamonds, including type-by-type outcomes, DiamondView patterns, and photoluminescence signatures. +order: 3 +category: identification +difficulty: advanced +icon: diamond +related: + - identification/treatments + - identification/synthetics + - species/diamond +tags: + - HPHT + - diamond + - DiamondView + - photoluminescence + - colour-treatment + +sections: + - title: Process and Conditions + content: | + High Pressure High Temperature (HPHT) annealing subjects natural diamonds to conditions + of 5–6 GPa pressure and 1700–2100 °C — replicating diamond formation conditions. The + mechanism differs by diamond type. Diamonds are encapsulated in a metal capsule (often + Fe or Co) to prevent graphitisation during treatment. + + Results from spectroscopic analyses of GE POL HPHT-annealed nominally type IIa diamonds + reveal that any yellow coloration in such stones is due to low concentrations of single + nitrogen, not observed in untreated diamonds of similar appearance (Fisher & Spits 2000). + + With increasing availability of treated and synthetic diamonds, gemologists benefit from + a complete understanding of the type system and what this information holds for + identification (Breeding & Shigley 2009). + callout: + type: info + title: Laboratory Testing Always Required + text: | + HPHT treatment cannot be detected by standard gem-testing instruments. LWUV fluorescence + provides a screening trigger; definitive identification requires FTIR, photoluminescence + spectroscopy at 77 K, and/or DiamondView imaging. Send to a specialist diamond laboratory. + + - title: Outcomes by Diamond Type + table: + caption: HPHT Treatment — Mechanisms and Results by Type + headers: + - Starting Diamond Type + - Mechanism + - HPHT Result + - Commercial Significance + rows: + - ["Type IIa (brown)", "Anneals plastic deformation (slip-plane graining) responsible for brown colour; removes ~270 nm absorption", "Near-colourless D–H colour range achievable", "Most common commercial application; high value uplift"] + - ["Type IaB (paired-N aggregates / N₂ pairs)", "Converts B-centres to H3 (N–V–N complex, 503 nm); creates yellow-green", "Yellow-green or yellow colour", "Less common"] + - ["Type Ib (isolated N)", "Modifies single-N centres", "Orange or brownish-orange", "Uncommon"] + - ["Type IIb (B-containing, blue)", "Removes residual N contamination; enhances blue", "Enhanced blue", "Rare; uncommon commercially"] + + - title: Key Spectroscopic Signatures + content: | + The N3 centre (415 nm, three-nitrogen + vacancy) is responsible for the blue LWUV + fluorescence seen in ~80% of natural gem diamonds (type Ia). HPHT-treated type IIa + diamonds frequently show **no blue LWUV fluorescence** — anomalous for gem-quality + colourless stones. This absence is the primary screening trigger. + + Additional spectroscopic changes: + - **270 nm absorption band disappears**: the deformation-related brown absorption in type IIa + is centred near 270 nm; HPHT annealing removes it + - **NV⁻ (637 nm) strong relative to NV⁰ (575 nm)**: the ratio of these photoluminescence + lines is diagnostic in treated type IIa at 77 K + - **H3 centre (503 nm / 503.2 nm spectroscopic precision)**: may become prominent in type + IaB treated stones; created from B-centres by HPHT + - **1344 cm⁻¹ peak in FTIR**: isolated-N absorption may appear in partially decoloured stones + + Sources: Fisher & Spits 2000 (10.5741/gems.36.1.42, [VERIFIED]); + Eaton-Magana et al. 2017 (10.5741/gems.53.3.262, [VERIFIED]); + Hainschwang et al. 2012 (10.5741/gems.48.4.252, [VERIFIED]); + Zhu 2024 (10.15506/jog.2024.39.1.24, [VERIFIED]) + + - title: Detection Methods — Full Protocol + table: + caption: HPHT Diamond Detection (simplest to most advanced) + headers: + - Method + - Finding + - Reliability + - Notes + rows: + - ["LWUV fluorescence (365 nm)", "Inert / no blue fluorescence in colourless stone — anomalous; ~80% of natural diamonds show at least weak blue", "Primary screening trigger", "Absence of fluorescence alone does not confirm HPHT; triggers lab testing"] + - ["Crossed polarisers (microscope)", "Anomalous birefringence: strain patterns, planar annealing fronts, cross-hatched strain halos distinct from untreated type IIa graining", "Strong indicator", "Requires dark-field polarised light microscopy"] + - ["FTIR spectroscopy", "Type IIa: no nitrogen absorption (<5 ppm N); 270 nm band absent; 1344 cm⁻¹ isolated-N peak may appear in partially decoloured stones; loss of A-centre peaks", "Instrument test", "Instrument accessible at major labs"] + - ["Photoluminescence (PL) at 77 K", "NV⁻/NV⁰ ratio diagnostic; specific centres absent or modified; H3 (503 nm) prominent in some treated types; specialist technique", "Advanced diagnostic", "Hainschwang 2012: NV⁻ 637 nm / NV⁰ 575 nm ratio characteristic"] + - ["DiamondView (SW UV 225 nm imaging)", "Irregular or cross-hatched green fluorescence sectors following original octahedral growth; distinct from CVD columnar striations and HPHT synthetic cuboctahedral sectors", "Most discriminating", "Specialist instrument; used at GIA, SSEF, Gübelin"] + - ["UV-Vis absorption spectroscopy", "N3 (415 nm) absent or weak; 270 nm band gone; single-N peaks at 270 nm may appear", "Instrument test", "Complements FTIR"] + + - title: DiamondView Pattern Summary (HPHT vs CVD vs Natural) + table: + headers: + - Diamond Type + - DiamondView Pattern + - Fluorescence Sector Pattern + - Phosphorescence + rows: + - ["Natural type Ia", "Octahedral growth sectors; blue N3 fluorescence", "Triangular/octahedral", "Rare; variable"] + - ["Natural type IIa", "Weak or irregular; may show no clear sector pattern", "Absent or faint", "Rare"] + - ["HPHT-treated natural type IIa", "Cross-hatched or irregular green sectors; modified original octahedral growth disrupted by treatment", "Irregular / cross-hatched", "Variable"] + - ["CVD synthetic", "Columnar/striated growth threads; no octahedral sectors", "Columnar (perpendicular to growth direction)", "Orange-red (diagnostic)"] + - ["HPHT synthetic", "Cuboctahedral growth sectors", "Cuboctahedral", "Variable"] + + - title: Disclosure and Stability + content: | + **Disclosure:** + - Mandatory under CIBJO, AGTA (code HPHT), and all major laboratory standards + - GIA practice: "HPHT Processed" laser-inscribed on the girdle (GE POL programme); + all major labs issue treatment notation — no standard grading report without disclosure + - LMHC: HPHT treatment is a permanent modification; must be disclosed at every + transaction in the supply chain + + **Stability:** + - Permanent; structural change cannot be reversed by normal wear, jewellery repair, + laser drilling, repolishing, or ultrasonic + - Thermally stable up to ~800 °C under 1 atm pressure + - Standard jeweller's torch temperatures (800–1000 °C) are safe for the diamond itself + + - title: Sources + content: | + - Fisher, D.; Spits, R.A. 2000. Spectroscopic Evidence of GE POL HPHT-Treated Natural + Type IIa Diamonds. *Gems & Gemology*. DOI: 10.5741/gems.36.1.42 [VERIFIED] + - Breeding, C.M.; Shigley, J.E. 2009. The "Type" Classification System of Diamonds and + Its Importance in Gemology. *Gems & Gemology*. DOI: 10.5741/gems.45.2.96 [VERIFIED] + - Overton, T.W.; Shigley, J.E. 2008. A History of Diamond Treatments. *Gems & Gemology*. + DOI: 10.5741/gems.44.1.32 [VERIFIED] + - Eaton-Magana, S.; Shigley, J.E.; Breeding, C.M. 2017. Observations on HPHT-Grown + Synthetic Diamonds: A Review. *Gems & Gemology*. DOI: 10.5741/gems.53.3.262 [VERIFIED] + - Hainschwang, T. et al. 2012. Photoluminescence at 77 K in treated diamonds. + *Gems & Gemology*. DOI: 10.5741/gems.48.4.252 [VERIFIED] + - Zhu, Y. et al. 2024. Spectral characteristics relevant to HPHT treatment identification. + *Journal of Gemmology*. DOI: 10.15506/jog.2024.39.1.24 [VERIFIED] diff --git a/docs/learn/identification/treatments-deep/lead-glass-ruby.yaml b/docs/learn/identification/treatments-deep/lead-glass-ruby.yaml new file mode 100644 index 0000000..c8e1ef4 --- /dev/null +++ b/docs/learn/identification/treatments-deep/lead-glass-ruby.yaml @@ -0,0 +1,110 @@ +title: Lead Glass-Filled Ruby — Deep Diagnostic Reference +description: Full detection protocol for composite (lead glass-filled) ruby, with nomenclature, durability, and disclosure standards. +order: 2 +category: identification +difficulty: advanced +icon: gem +related: + - identification/treatments + - identification/inclusions + - species/corundum +tags: + - lead-glass + - composite-ruby + - fracture-filling + - EDXRF + +sections: + - title: Process and Composition + content: | + Heavily fractured, near-gem to sub-gem quality corundum is placed in a high-lead silicate + glass melt (PbO content typically 70–95% by weight) at temperatures of 900–1000 °C. + The low-viscosity, high-RI Pb-glass (RI ~1.74–1.78) flows into open fractures by + capillary action over multiple fill cycles (flux-and-fill). + + In early 2004, the GAAJ laboratory in Japan issued a lab alert about rubies with large + numbers of fractures filled with high-lead-content glass, which made them appear very + transparent. Clarity enhancement of ruby by lead glass filling was one of the most + significant developments of the 2000s (McClure et al. 2006; McClure et al. 2010). + + Glass composition: PbO 70–95%; SiO₂, Al₂O₃; variable TiO₂, CaO; some formulations + include cobalt oxide to add blue tinting to mask brownish or orange body tones. + callout: + type: error + title: Composite Ruby — Not a Treated Ruby + text: | + Stones containing significant glass fill are composite materials, not treated rubies. + CIBJO and GIA require the term "composite ruby" or "glass-filled ruby". The term + "enhanced ruby" is insufficient and misleading. + + Damage agents: jeweller's torch temperatures (glass melts/bubbles), lemon juice + (etches glass within minutes), pickling solutions, ultrasonic cleaning, steam. + + - title: Physical Properties of Composite Ruby + table: + caption: Composite Ruby vs Natural Ruby — Physical Comparison + headers: + - Property + - Natural Ruby + - Composite Ruby + rows: + - ["RI", "1.762–1.770 (uniaxial −)", "Mixed: ruby RI + glass RI ~1.74–1.78"] + - ["SG", "~4.00", "3.60–3.80 (depends on glass volume fraction)"] + - ["Lustre", "Adamantine to vitreous", "Areas of vitreous lustre from glass patches"] + - ["UV fluorescence (SWUV)", "Variable red/orange Cr fluorescence", "Glass may fluoresce chalky greenish"] + - ["Acid resistance", "Unaffected by dilute acid", "Glass etched and clouded by lemon juice or HCl"] + + - title: Detection Methods — Full Protocol + table: + caption: Lead Glass-Filled Ruby Detection (simplest to most advanced) + headers: + - Method + - Diagnostic Feature + - Reliability + - Notes + rows: + - ["10× loupe, reflected light", "Glassy/vitreous lustre patches interrupting ruby's adamantine lustre; depressions or pits where glass has eroded", "Strong indicator", "Most accessible first check"] + - ["Darkfield microscope (40–60×) — blue/orange flash", "Blue flash when tilted one way, orange flash the other, at fracture–ruby interface (thin-film interference from glass fill–corundum boundary)", "Most reliable in-lab indicator", "Primary diagnostic; described in McClure et al. 2006"] + - ["Gas bubbles (40–60×, darkfield)", "Spherical or elongated bubbles trapped in glass fill — not present in natural growth features (feathers, fingerprints)", "Diagnostic", "Natural features never contain spherical bubbles"] + - ["Flow structures (40–60×)", "Swirling patterns in glass under darkfield; absent in natural feathers and liquid inclusions", "Diagnostic", "Confirms glass rather than resin"] + - ["Hydrostatic SG", "Values <3.90 in a ruby-sized stone strongly suggest significant glass content", "Strong screening", "Natural ruby ~4.00; composite values as low as 3.60"] + - ["Chelsea Colour Filter (cobalt variant)", "If cobalt in glass: red reaction from Co; combined glass-fill + cobalt gives anomalous result vs pure Cr ruby", "Useful if cobalt glass suspected", "Natural ruby reacts red from Cr only"] + - ["SW UV fluorescence", "Lead glass frequently fluoresces chalky greenish or shows abnormal fluorescence patterns not seen in natural ruby inclusions", "Supporting", "Not conclusive alone"] + - ["Acid sensitivity test (destructive)", "A drop of lemon juice (citric acid, pH ~2) or dilute HCl on pavilion girdle: glass etches and clouds within minutes; corundum unaffected", "Conclusive if positive", "Destructive — use only on obscure area, when other evidence inconclusive"] + - ["EDXRF", "Elevated Pb signal at surface or in fractures — Pb is diagnostic of glass fill; non-destructive, rapid", "Definitive confirmation", "Most labs use EDXRF as first confirmatory step"] + - ["LA-ICP-MS", "Quantifies Pb at trace and major element levels; unambiguous confirmation of glass fill", "Definitive", "Used in research-level reports"] + + - title: Disclosure and Nomenclature + content: | + - **CIBJO Blue Book**: must be described as "composite ruby" or "glass-filled ruby", + NOT simply as "ruby" + - **GIA**: does not issue standard ruby grading reports for composite rubies; issues a + "Composite Ruby" identification report with statement of glass content + - **AGTA code**: F (filling) + - **LMHC**: composite rubies require disclosure at every point in the supply chain; + "enhanced ruby" is considered insufficient; correct terminology is "glass-filled + composite ruby" + - **Gem-A**: distinction between "treated ruby" (heated, oiled) and "glass-filled + composite ruby" is categorically important — these are different disclosure situations + and different value categories + + - title: Stability and Care + table: + caption: Lead Glass-Filled Ruby — Care Warnings + headers: + - Risk Factor + - Effect + - Care Instruction + rows: + - ["Jeweller's torch / heat", "Glass melts or bubbles at working temperatures; filling destroyed", "No jeweller's torch; no heat repairs"] + - ["Dilute acids (lemon juice, citric)", "Glass etches and clouds within minutes", "No acid-based cleaners; avoid fruit juice contact"] + - ["Ultrasonic cleaning", "Vibration loosens glass from fractures; can cause fracturing", "Never ultrasonic"] + - ["Steam cleaning", "Thermal shock may crack glass–ruby interface", "Avoid steam"] + - ["Repolishing", "Safe if done correctly; may expose new fracture mouths", "Proceed with caution"] + + - title: Sources + content: | + - McClure, S.F. et al. 2006. Identification and Durability of Lead Glass-Filled Rubies. + *Gems & Gemology*. DOI: 10.5741/gems.42.1.22 [VERIFIED] + - McClure, S.F. et al. 2010. Gemstone Enhancement and Its Detection in the 2000s. + *Gems & Gemology*. DOI: 10.5741/gems.46.3.218 [VERIFIED] diff --git a/docs/learn/identification/treatments.yaml b/docs/learn/identification/treatments.yaml index b389447..edc057b 100644 --- a/docs/learn/identification/treatments.yaml +++ b/docs/learn/identification/treatments.yaml @@ -1,5 +1,5 @@ title: Gemstone Treatments -description: Heat treatment, filling, diffusion, coating, and detection methods for treated gemstones. +description: Heat treatment, filling, diffusion, coating, and detection methods for treated gemstones — with per-species diagnostic depth. order: 5 category: identification difficulty: intermediate @@ -10,6 +10,10 @@ related: - market/professional-practice - care/gem-care-durability - species/diamond + - identification/treatments-deep/beryllium-diffusion + - identification/treatments-deep/lead-glass-ruby + - identification/treatments-deep/hpht-diamond + - identification/treatments-deep/cvd-diamond tags: - heat-treatment - market/disclosure @@ -27,13 +31,14 @@ sections: title: Disclosure Requirement text: | All gemstone treatments must be disclosed at the point of sale. Major laboratories - (GIA, Gubelin, SSEF) provide treatment reports. Undisclosed treatments are - considered fraudulent. + (GIA, Gübelin, SSEF) provide treatment reports. Undisclosed treatments are + considered fraudulent in most jurisdictions. - - title: Heat Treatment + - title: Heat Treatment of Corundum content: | - The most common treatment, heat treatment permanently alters colour and clarity - by modifying the chemical state of chromophores or dissolving silk inclusions. + The most common treatment. Heat permanently alters colour and clarity by modifying + chromophore chemistry or dissolving silk inclusions. Plain heating (H) and flux-assisted + heating with borax (H(a)) are now classified separately by Gem-A and major laboratories. table: caption: Common Heat Treatments headers: @@ -41,182 +46,413 @@ sections: - Effect - Temperature Range rows: - - ["Blue sapphire", "Improves blue colour, dissolves silk", "1400-1800°C"] - - ["Ruby", "Improves red colour, dissolves silk", "1200-1800°C"] - - ["Tanzanite", "Changes brown to blue-violet", "450-650°C"] - - ["Aquamarine", "Removes green tint (yellow component)", "400-450°C"] - - ["Citrine", "Heat-treated amethyst", "450-500°C"] - - ["Zircon", "Creates blue colour from brown", "900-1000°C"] + - ["Blue sapphire", "Improves blue colour, dissolves silk", "1400–1800 °C"] + - ["Ruby", "Improves red colour, dissolves silk", "1200–1800 °C"] + - ["Tanzanite", "Changes brown to blue-violet", "450–650 °C"] + - ["Aquamarine", "Removes green tint (yellow component)", "400–450 °C"] + - ["Citrine", "Heat-treated amethyst", "450–500 °C"] + - ["Zircon", "Creates blue colour from brown", "900–1000 °C"] subsections: - - title: Detection Signs + - title: Diagnostic Inclusion Changes (Darkfield 40–60×) content: | - - Dissolved or partially dissolved silk (dotted lines) - - Stress fractures around solid inclusions - - Altered/melted inclusions - - "Halo" fractures around zircon crystals - - Colour concentrations along fractures - - Altered absorption spectrum - - - title: Fracture Filling + - **Dissolved silk** — rutile needles partially resorbed; appear as dotted trails + or "fingerprint" remnants along former needle orientation; diagnostic for heat + above 1400 °C + - **Discoid (halo) fractures** — disc-shaped stress fractures around zircon, + apatite, or calcite inclusions from thermal expansion; highly diagnostic for + heat above 1600 °C + - **Flux residue droplets** — colourless rounded glass blebs at fracture mouths + (borax); show anomalous birefringence under crossed polars; diagnostic for + H(a) flux-healing treatment + - **Partially healed fractures** — feathered, partially recrystallised fractures + with residual fluid inclusions; distinct from natural growth features + + - title: FTIR Evidence for Unheated Sapphire + content: | + Goethite (dehydrates 300–325 °C) and diaspore (dehydrates 525–550 °C) have + diagnostic OH absorption peaks at ~3300–3400 cm⁻¹ that vanish on heating. + Their absence in stones from origins known to contain them is strong evidence + for heat treatment (Krzemnicki et al. 2023, 10.3390/min13121557, [VERIFIED]). + + A 3232 cm⁻¹ FTIR band identifies heat-treated metamorphic-type blue sapphires + (Delaunay 2024, 10.15506/jog.2024.39.1.33, [VERIFIED]). + + - title: Disclosure Status + content: | + - **H (plain heat)**: widely accepted; CIBJO and Gem-A require disclosure but value + impact is minimal for corundum + - **H(a) (flux/fracture healing)**: must be disclosed separately; value impact + is greater; GIA and Gem-A treat this as distinct from simple heating + - "No evidence of heat treatment" (NTE) on a laboratory report commands a + significant premium; verify by the inclusion criteria above + + - title: Beryllium Diffusion — Lattice Diffusion (Sapphire) + content: | + Commercialised around 2001. Beryllium (Be²⁺) ions diffuse through the full corundum + lattice at 1700–1800 °C producing intense orange, yellow, or padparadscha colours. + Distinct from titanium surface diffusion in penetration depth. + callout: + type: warning + title: Standard Tools Are Insufficient + text: | + Beryllium diffusion cannot be reliably detected by standard gem-testing instruments. + LA-ICP-MS or SIMS is required for a definitive result. All corundum sold as + padparadscha or vivid-orange sapphire should carry a laboratory report. + + Full detection protocol: see Deep Reference — Beryllium Diffusion. + subsections: + - title: Process Overview + content: | + Rough is packed in BeO or chrysoberyl powder and fired at 1700–1800 °C in an + oxidising atmosphere for 12–100 hours. Be²⁺ (ionic radius 0.27 Å) penetrates + the full lattice, unlike Ti or Cr which remain within ~50–100 µm of the surface. + Colour is **lattice-deep** — re-cutting does not remove it. + + Sources: Emmett et al. 2003 (10.5741/gems.39.2.84, [VERIFIED]); + Emmett et al. 2023 (10.5741/gems.59.3.268, [VERIFIED]) + + - title: Key Detection Points + content: | + - **10× loupe**: colour may appear suspiciously homogeneous; immersion spider-web + is faint (if present) — less pronounced than Ti surface diffusion + - **LA-ICP-MS**: Be >1–2 ppm in orange/yellow corundum is diagnostic; natural + corundum contains <0.1 ppm Be + - **SIMS**: diffusion gradient (high at surface, declining inward) confirms treatment + - **Stability**: permanent; colour survives repolishing, ultrasonic, and steam + - **Disclosure**: AGTA code U; GIA reports "lattice diffusion — beryllium present" + + - title: Surface Diffusion vs Lattice Diffusion — The Depth Distinction content: | - Surface-reaching fractures are filled with glass, oil, or resin to improve - apparent clarity. This treatment requires special care in handling. + The critical diagnostic difference between titanium surface diffusion (Ti, pre-2001, + now rare) and beryllium lattice diffusion is colour penetration depth and the resulting + immersion microscopy appearance. table: - caption: Types of Fillers + caption: Surface vs Lattice Diffusion — Key Differences headers: - - Filler Type - - Gemstone - - Stability + - Property + - Ti Surface Diffusion + - Be Lattice Diffusion rows: - - ["Oil (cedar oil)", "Emerald", "Can dry out over time"] - - ["Opticon/resin", "Emerald", "More stable than oil"] - - ["Lead glass", "Ruby, Sapphire", "Damaged by heat, acids"] - - ["Polymer resins", "Various", "Variable"] + - ["Penetration depth", "50–100 µm (skin only)", "Full lattice depth (mm scale)"] + - ["Immersion spider-web pattern", "Strongly visible under darkfield", "Faint or absent"] + - ["Re-cutting effect", "Removes colour on any recut facet", "No effect on colour"] + - ["Definitive detection", "Immersion microscope (practical)", "LA-ICP-MS / SIMS required"] + - ["Stability", "Fragile to repolishing", "Permanent"] + - ["AGTA code", "U", "U"] subsections: - - title: Detection Signs + - title: Spider-Web Test (Ti Surface Diffusion) content: | - - Flash effect (orange/blue flashes in fractures) - - Gas bubbles in filler - - Flow structures - - Different RI in filled areas - - Blue glow under UV (some resins) + Immerse the stone in di-iodomethane (or water) and observe under darkfield illumination + at 40–60× magnification. In titanium surface-diffused sapphire, colour accumulates as + a visible network following facet edges — the "spider-web". Where two surfaces meet, + the diffused zone doubles in thickness and appears darker. - - title: Lead Glass-Filled Rubies + Scratches, chips, or abrasions on facets will expose colourless material beneath. + Any repolishing through a facet removes colour entirely from that facet. + + Source: Kane et al. 1990 (10.5741/gems.26.2.115, [VERIFIED]) + + - title: Fracture Filling of Emerald + content: | + Emeralds typically contain abundant surface-reaching fractures ("jardin"). Cedar oil + (RI ~1.51) and Opticon resin (RI ~1.55) are the most common fillers. They are detected + by the flash effect under darkfield and FTIR spectroscopy. + subsections: + - title: Detection Methods + table: + caption: Emerald Fracture Filling Detection + headers: + - Method + - Finding + rows: + - ["10× loupe, reflected light", "Lustre difference at fracture mouths; slightly vitreous vs adamantine"] + - ["Darkfield microscope (40×) — flash effect", "Orange/yellowish-orange iridescent flash at filler–crystal interface when tilted (primary in-lab test)"] + - ["Gas bubbles / flow structures", "Spherical bubbles or swirling patterns in polymer; absent in natural fluid inclusions"] + - ["UV fluorescence (LWUV/SWUV)", "Opticon and resins: chalky-blue or yellowish-green glow; cedar oil: negligible fluorescence"] + - ["FTIR spectroscopy", "Resins: C–H stretching ~3000–3050 cm⁻¹; C=O stretching ~1700–1730 cm⁻¹; unfilled emerald shows no organic absorptions — definitive"] + + Source: Kammerling et al. 1991 (10.5741/gems.27.2.70, [VERIFIED]) + + - title: LMHC Fracture-Fill Disclosure Scale + content: | + The Laboratory Manual Harmonisation Committee (LMHC) has established a harmonised + grading scale for emerald fracture filling [PARTIALLY_SUPPORTED — institutional document; + not API-retrievable as peer-reviewed paper; cite via https://www.lmhc-gemmology.org]: + + - **F1 (None)**: no filler; unfilled stone + - **F2 (Minor/Insignificant)**: trace filler; no material effect on appearance + - **F3 (Moderate)**: filler clearly present; requires disclosure + - **F4 (Significant)**: substantial filling; strongly impacts apparent clarity + - **F5 (Prominent/Prominent+)**: extreme filling; stone may approach composite character + + Cedar oil at minor level is widely accepted but Gem-A and CIBJO now require disclosure + of all fillings. Polymer (Opticon, epoxy) filling always requires disclosure. + + - title: Stability and Care + content: | + - **Cedar oil**: temporary; dries out over months to years; avoid ultrasonic, steam, solvents + - **Opticon/epoxy**: more stable; dissolved by acetone, alcohol; avoid ultrasonic, torch + - Advise all clients to avoid ultrasonic, steam, and alcohol-based cleaners for filled emeralds + + - title: Lead Glass-Filled Ruby (Composite Ruby) callout: type: error - title: Lead Glass-Filled Rubies + title: Composite Ruby — Distinct from Treated Ruby text: | - Heavily fractured, low-quality ruby is sometimes filled with high-RI lead glass. - These stones can contain more glass than ruby and are extremely fragile. They - are damaged by heat, ultrasonic cleaning, and even lemon juice. + Heavily fractured low-quality corundum filled with high-lead-content glass (PbO 70–95%) + is a composite material. CIBJO and GIA require the term "composite ruby" or "glass-filled + ruby" — not "treated ruby" or "enhanced ruby". Stones can contain more glass than ruby. + + Damage agents: jeweller's torch, dilute acids (lemon juice), ultrasonic, steam. - - title: Diffusion Treatment + Full detection protocol: see Deep Reference — Lead Glass-Filled Ruby. + subsections: + - title: Key Properties and Detection Summary + content: | + - **SG**: depressed from natural ruby ~4.00 to composite values as low as 3.60–3.80 + - **Blue/orange flash effect** (darkfield, 40–60×): vivid blue flash one way, orange + flash the other, at the glass–ruby interface — the most reliable in-lab indicator + - **Gas bubbles**: spherical bubbles in glass fill; never in natural growth features + - **SW UV**: lead glass fluoresces chalky greenish — abnormal for ruby inclusions + - **EDXRF**: elevated Pb at surface is diagnostic; non-destructive, rapid + - **Acid test (destructive)**: lemon juice etches glass within minutes; corundum unaffected + + Source: McClure et al. 2006 (10.5741/gems.42.1.22, [VERIFIED]) + + - title: HPHT Diamond Colour Treatment content: | - Elements are diffused into the stone at high temperatures to alter colour. - This can be shallow (surface) or deep (lattice diffusion). - table: - caption: Types of Diffusion - headers: - - Type - - Element - - Result - rows: - - ["Surface diffusion", "Titanium (Ti)", "Blue colour in sapphire (shallow)"] - - ["Lattice diffusion", "Beryllium (Be)", "Orange/yellow/pink sapphire (deep)"] - - ["Lattice diffusion", "Cobalt (Co)", "Blue glass-filled stones"] + HPHT annealing (5–6 GPa, 1700–2100 °C) can decolourise brown Type IIa diamonds to + near-colourless (D–H) or create fancy colours in other types. Cannot be detected by + standard tools — laboratory testing is required. + callout: + type: info + title: Deep Reference Available + text: | + Full detection protocol, type-by-type outcome table, DiamondView pattern comparison, + and photoluminescence signature detail: see Deep Reference — HPHT Diamond Treatment. subsections: - - title: Detection Methods + - title: Key Signatures + content: | + - **Absent LWUV blue fluorescence**: ~80% of natural gem diamonds show blue LWUV; + HPHT-treated type IIa are typically inert — primary screening trigger + - **FTIR**: type IIa signature (no N >5 ppm); 270 nm brown absorption absent after + treatment; 1344 cm⁻¹ isolated-N peak may appear in partially decoloured stones + - **DiamondView**: cross-hatched or irregular green sectors (modified octahedral growth); + distinct from CVD columnar striations + - **PL at 77 K**: NV⁻ (637 nm) strong relative to NV⁰ (575 nm) in treated type IIa; + H3 (503 nm) may be prominent in type IaB treated stones + - **Stability**: permanent; disclose with AGTA code HPHT + + Sources: Fisher & Spits 2000 (10.5741/gems.36.1.42, [VERIFIED]); + Eaton-Magana et al. 2017 (10.5741/gems.53.3.262, [VERIFIED]) + + - title: CVD Diamond Detection + content: | + CVD synthetic diamonds grow in columnar layers from carbon-bearing gas plasma at low + pressure and 700–1000 °C. They are typically Type IIa and require specialist laboratory + tools to distinguish from natural or HPHT-treated stones. + callout: + type: info + title: Deep Reference Available + text: | + Full detection protocol, comparison table (CVD vs HPHT vs natural), secondary HPHT + complication note, and citation for orange-red phosphorescence: see Deep Reference — + CVD Diamond Detection. + subsections: + - title: Key Diagnostic Features content: | - - **Surface diffusion**: Immersion reveals colour concentration along facet edges and girdle - - **Beryllium diffusion**: LIBS or LA-ICP-MS analysis required for definitive detection - - Colour distribution patterns may indicate treatment + - **DiamondView (225 nm SW UV)**: orange-red phosphorescence (diagnostic when present); + columnar/striated growth threads — no octahedral growth sectors + (Zhang et al. 2024, 10.3390/cryst14090804, [VERIFIED] — resolves VERIFIED.md F-03 flag) + - **PL at 77 K**: SiV⁻ doublet at 736.9/736.6 nm characteristic of CVD growth; + rarely present in natural or HPHT-treated stones + - **FTIR**: Type IIa signature; NV-H (3123 cm⁻¹) in some N-doped CVD samples + - **Disclosure**: must be disclosed as "synthetic diamond" or "laboratory-grown diamond"; + "cultured" or "cultivated" are not acceptable per CIBJO + + Sources: Martineau et al. 2004 (10.5741/gems.40.1.2, [VERIFIED]); + Zhang et al. 2024 (10.3390/cryst14090804, [VERIFIED]) - - title: Coating and Surface Treatments + - title: Pearl Colour Treatment + content: | + Pearl colour treatments include gamma irradiation (darkening the bead nucleus via MnCO₃ + oxidation) and dyeing with organic dyes or silver nitrate. Irradiated Akoya pearls are + the most commercially significant treatment requiring detection. + subsections: + - title: Gamma Irradiation (Akoya) + content: | + Pearls are exposed to ⁶⁰Co gamma-ray sources at 0.1–100 kGy. Radiation oxidises + MnCO₃ in the bead nucleus to MnO₂ (dark brown/black), creating a dark body colour + visible through the nacre. The radiation also denatures conchiolin, detectable by ESR. + + **ESR (Electron Spin Resonance)** detects the CO₂⁻ radical (g-factor 2.001 ± 0.002) + from radiation damage to carbonate — the gold-standard diagnostic for irradiation. + **LWUV fluorescence**: irradiated Akoya show no/very weak fluorescence (radiation + damages conchiolin fluorophore); natural black Tahitian show reddish-pink/red glow. + **EDXRF**: elevated Ag = silver-nitrate dye; Mn/Fe nucleus profiling for irradiation. + **X-radiography**: dark nucleus in irradiated Akoya vs involvement of nacre and nucleus + in naturally dark Tahitian pearls. + + Source: Kim et al. 2012 (10.5741/gems.48.4.292, [VERIFIED]) + + - title: Silver Nitrate Dyeing + content: | + Pearls are immersed in AgNO₃ solution then exposed to H₂S gas or sunlight, + precipitating Ag₂S (silver sulphide) in the nacre layers, producing blue-grey to + black colour. [PARTIALLY_SUPPORTED — Ag₂S mechanism is established trade knowledge; + the specific precipitation chemistry details are not independently confirmed to + peer-reviewed paper level at this time; present as trade knowledge.] + + Detection: EDXRF detects elevated Ag; drill-hole inspection shows dye concentration + at and around the entry point. + + Source: Karampelas et al. 2007 (10.12681/bgsg.16720, [VERIFIED]) + + - title: Disclosure and Stability + content: | + - **Disclosure**: CIBJO and Gem-A require disclosure of all colour treatments in pearls; + irradiated Akoya sold as Tahitian substitutes constitutes fraud + - **Irradiation stability**: permanent at normal temperatures; some fading in prolonged + strong UV; nucleus darkening is stable + - **Organic dyes**: fade in light, heat, sweat, cosmetics; variable stability + - **Silver nitrate**: Ag₂S relatively stable; altered by strong reducing agents + - Avoid ultrasonic, bleaches, steam for all treated pearls + + - title: Jade Treatments (A-jade, B-jade, C-jade) + content: | + Jadeite treatments range from traditional waxing (A-jade, accepted) to aggressive + bleaching, polymer impregnation (B-jade), and dyeing (C-jade). The A/B/C classification + is standard in the trade. table: + caption: Jadeite Treatment Classification headers: + - Type - Treatment - - Description - - Detection + - Status rows: - - ["Thin-film coating", "Metallic oxide layer for colour", "Wear marks, different colour in scratches"] - - ["Backing", "Foil or paint behind stone", "Visible in mounted stones, immersion"] - - ["Waxing", "Surface wax for lustre", "Hot needle test, solvent test"] - - ["Dyeing", "Colour added to porous stones", "Colour concentrations, swab test"] + - ["A-jade", "Untreated (waxing accepted)", "Natural; highest commercial value"] + - ["B-jade", "Bleached in acid + vacuum polymer impregnation", "Treated; must be disclosed"] + - ["C-jade", "Dyed (Cr-green or other pigments)", "Treated; must be disclosed"] + - ["B+C-jade", "Both bleaching/impregnation and dyeing", "Treated; must be disclosed"] + subsections: + - title: Detection + content: | + **B-jade process**: jadeite is immersed in dilute HCl or H₂SO₄ for days to weeks + (bleaching), then vacuum-impregnated with epoxy resin (restores structural integrity). + The acid permanently damages the interlocking grain structure. + + **Detection methods:** + - **10× loupe**: polymer filaments or threads along grain boundaries (reticulate pattern + absent in A-jade); C-jade shows colour concentrated in fractures and grain boundaries + - **SW UV**: B-jade shows chalky blue fluorescence from polymer; A-jade inert or faint + whitish glow + - **Chelsea filter**: C-jade (Cr-green dye) reacts red; A-jade (Fe-green) does not + - **FTIR (definitive)**: C–H stretching at 2800–3000 cm⁻¹; C=O at ~1700 cm⁻¹; + absent in untreated jadeite + + Source: Fritsch et al. 1992 (10.5741/gems.28.3.176, [VERIFIED]) + + - title: Disclosure and Stability + content: | + - **CIBJO**: "jade" without qualification implies A-jade; B and C must specify treatment + - **AGTA codes**: B (bleaching), D (dyeing), F (filling) as applicable + - **Gem-A**: "treated jadeite" with treatment type specified + - B-jade: avoid ultrasonic (acid-damaged matrix permanently weakened); solvents dissolve + polymer; C-jade organic dyes may fade in light + + - title: Thin-Film Coating (Mystic Topaz) + content: | + Colourless topaz is coated with a multilayer TiO₂/SiO₂/Nb₂O₅ thin-film stack by PVD + (Physical Vapour Deposition) at low temperatures. The multilayer interference film produces + vivid iridescent "rainbow" colours varying with viewing angle. + + [PARTIALLY_SUPPORTED — mystic topaz TiO₂/SiO₂ multilayer PVD specifics are from industry + literature; Shigley et al. 2012 (10.5741/gems.48.1.18, [VERIFIED]) confirms the detection + principle and coated gem methodology via study of coated CZ (Diamantine).] + subsections: + - title: Detection and Stability + content: | + **Detection:** + - **10× loupe**: visible chipping or abrasion at facet junctions; underlying colourless + topaz visible through scratches + - **Angle-dependent colour shift**: colour pattern shifts predictably with angle + (thin-film interference) — different from random play-of-colour of precious opal + - **Acetone swab (cautious, on pavilion)**: some coatings lift on contact + - **EDXRF**: anomalous Ti, Nb, or Si at the surface — topaz itself contains neither + + **Stability:** + - Poor wear resistance; coating hardness lower than topaz (Mohs 8); + daily wear damages coating at exposed facet edges; avoid ultrasonic, steam, solvents + - Disclosure: CIBJO requires "coated"; AGTA code C; GIA: "surface coating present" - title: Irradiation content: | - Exposure to radiation (gamma rays, electrons, neutrons) can create or modify colour. + Exposure to radiation (gamma rays, electrons, neutrons) creates or modifies colour. table: headers: - Gemstone - Starting Colour - Result rows: - - ["Blue topaz", "Colourless", "Blue (followed by heat)"] + - ["Blue topaz", "Colourless", "Blue (followed by heat annealing for stability)"] - ["Fancy diamond", "Various", "Green, blue, yellow, pink"] - - ["Kunzite", "Pink", "Deeper pink (may fade)"] + - ["Kunzite", "Pink", "Deeper pink (may fade in light)"] - ["Smoky quartz", "Colourless", "Brown/smoky"] + - ["Akoya pearl", "Light cream", "Dark grey to black (nucleus darkening)"] + + - title: Quench-Crackling of Quartz + callout: + type: info + title: Confidence C — Citation Gap + text: | + The process and detection features below are from established gemmological teaching + material (consistent with Read 7th ed. and Gem-A textbooks). No peer-reviewed + journal paper dedicated to quench-crackled quartz identification was returned by API + in the R5 research session. Crossref returned a dictionary entry (DOI + 10.1007/978-3-540-72816-0_17924) confirming this as a defined trade category. + Present with caution; do not cite as peer-review-verified. + content: | + Rock crystal (colourless quartz) is heated to 300–400 °C then rapidly quenched in cold + water or a dye solution. Thermal shock creates a dense internal fracture network + which absorbs dye. Sold as "cherry quartz", "blue quartz", or "crackled quartz". + subsections: + - title: Detection + content: | + - **10× loupe**: dense, uniform, pervasive fracture network with no preferred + crystallographic orientation — diagnostic; contrast with sparse, irregular, + curved natural quartz fractures + - **Transmitted light**: dye visible only in fractures; quartz crystals between + fractures remain colourless; no natural quartz variety has colour only in fractures + - **UV fluorescence**: organic dyes may fluoresce; natural quartz inclusions do not + - **FTIR / Raman**: organic C–H peaks at ~3000 cm⁻¹; dye-specific peaks; pure + quartz shows no organic absorptions - - title: Treatment Acceptance + This material is an imitation/simulation: CIBJO requires "dyed crackled quartz" + or "quench-crackled quartz" — not a natural quartz variety designation. + + - title: Treatment Acceptance Summary comparison: items: - title: Widely Accepted variant: success points: - Heat treatment (corundum) - - Oil in emerald (cedar oil) + - Oil in emerald (cedar oil, minor) - Waxing (turquoise, jade) - - title: Accepted with Disclosure + - title: Accepted with Full Disclosure variant: warning points: - - Resin filling - - Beryllium diffusion - - Irradiation - - title: Controversial + - Resin filling (polymer) — emerald + - Beryllium lattice diffusion + - Irradiation (most types) + - HPHT diamond (permanent — must disclose) + - title: Controversial / Explicit Disclosure Required variant: danger points: - - Lead glass filling - - Surface diffusion - - Coatings - - - title: HPHT Diamond Treatment - content: | - High Pressure High Temperature (HPHT) treatment can permanently alter diamond colour. - Originally developed for industrial applications, it's now used to improve gem-quality - diamonds. - subsections: - - title: Type IIa Diamonds - content: | - Type IIa diamonds (nitrogen-free) can be decolourised by HPHT treatment: - - - **Starting material**: Brown Type IIa diamonds - - **Result**: Near-colourless (D-F colour possible) - - **Mechanism**: Removes plastic deformation that causes brown colour - - **Stability**: Permanent; colour won't revert - - - title: Fancy Colour Creation - table: - headers: - - Starting Type - - HPHT Result - - Mechanism - rows: - - ["Type Ia (cape series)", "Intense yellow or green-yellow", "Modifies nitrogen centres"] - - ["Type IaB", "Yellow or green", "Creates H3/H4 centres"] - - ["Type Ib", "Orange or brownish-orange", "Modifies isolated nitrogen"] - - ["Type IIa (brown)", "Colourless or pink", "Removes deformation"] - - ["Type IIb", "Enhanced blue", "Possible but uncommon"] - - - title: Detection Methods - content: | - HPHT-treated diamonds can be identified by: - - - **Photoluminescence spectroscopy**: Characteristic centres - - **Infrared spectroscopy**: Modified nitrogen aggregation - - **DiamondView imaging**: Unusual fluorescence patterns - - **Graining patterns**: May show altered internal structure - - **Laboratory testing required**: Cannot be detected with standard tools - - - title: Cobalt Diffusion - content: | - Cobalt can be diffused into gems during high-temperature treatment, most commonly - in lead glass-filled rubies where it creates artificial blue colour in the glass. - subsections: - - title: Cobalt in Glass-Filled Stones - content: | - Some lead glass fillings contain cobalt to add blue colour: - - - Creates bluish tinge that masks brown/orange body colours - - Concentrated in fractures and surface areas - - Can be mistaken for better quality material - - Flash effect may show blue rather than typical orange - - - title: Detection - content: | - - **Blue flash effect**: Unusual blue colour in fractures under magnification - - **Chelsea filter**: Strong red reaction from cobalt - - **Spectroscopy**: Cobalt absorption bands (around 550nm) - - **Chemical analysis**: LIBS or LA-ICP-MS confirms cobalt presence + - Lead glass filling (composite ruby) + - Ti surface diffusion + - Thin-film coatings + - B-jade / C-jade - title: Treatment Stability Chart table: @@ -227,35 +463,34 @@ sections: - Sensitive To - Care Notes rows: - - ["Heat (corundum)", "Permanent", "N/A", "No special care needed"] - - ["Heat (zircon)", "Stable", "Extreme heat may affect", "Avoid jeweller's torch"] - - ["Oil (emerald)", "Temporary", "Heat, solvents, time", "Re-oil periodically; avoid ultrasonic"] - - ["Resin (emerald)", "Semi-permanent", "Heat, strong solvents", "Avoid ultrasonic and steam"] - - ["Lead glass (ruby)", "Fragile", "Heat, acids, ultrasonic", "Extreme care required"] + - ["Heat (corundum — plain H)", "Permanent", "N/A", "No special care needed"] + - ["Flux heating H(a)", "Permanent colour; flux residues stable", "N/A", "Disclose separately from plain H"] + - ["Heat (zircon)", "Stable", "Extreme heat", "Avoid jeweller's torch"] + - ["Oil (emerald)", "Temporary", "Heat, solvents, time", "Re-oil periodically; no ultrasonic"] + - ["Resin (emerald)", "Semi-permanent", "Heat, strong solvents", "No ultrasonic; no steam"] + - ["Lead glass (ruby)", "Fragile", "Heat, acids, ultrasonic", "Extreme care; no ultrasonic or acids"] - ["Beryllium diffusion", "Permanent", "N/A", "No special care needed"] - - ["Surface diffusion", "Shallow only", "Repolishing removes", "Avoid recutting"] - - ["Irradiation (topaz)", "Usually stable", "Some may fade", "Stable once processed"] - - ["Coating", "Fragile", "Abrasion, solvents", "Will wear off over time"] + - ["Ti surface diffusion", "Fragile", "Repolishing removes colour", "Avoid recutting"] + - ["Irradiation (topaz)", "Usually stable", "Strong UV light (some types)", "Stable once processed"] + - ["Coating (mystic topaz)", "Fragile", "Abrasion, solvents, ultrasonic", "Will wear off at facet edges"] - ["HPHT (diamond)", "Permanent", "N/A", "No special care needed"] + - ["B-jade polymer", "Moderate; matrix permanently weakened", "Solvents, ultrasonic, impact", "No ultrasonic; handle carefully"] + - ["Pearl irradiation", "Stable (normal conditions)", "Prolonged UV", "Avoid bleaches; gentle care only"] - title: Treatment Stability Warning callout: type: warning - title: Unstable Treatments + title: Unstable Treatments Requiring Ongoing Care text: | - Some treatments require ongoing care or will degrade: + - **Oil in emerald**: may dry out; requires periodic re-oiling + - **Lead glass filling**: damaged by heat, acids (even lemon juice), and ultrasonic + - **Coatings (mystic topaz)**: wear off at facet edges; cannot be cleaned aggressively + - **Some irradiation**: certain colours (kunzite, some topaz) may fade in light + - **B-jade**: ultrasonic cleaning dangerous; acid-damaged matrix permanently weakened - - **Oil in emerald**: May dry out; requires periodic re-oiling - - **Lead glass filling**: Extremely fragile; damaged by heat, acids, even lemon juice - - **Coatings**: Will wear off; cannot be cleaned aggressively - - **Some irradiation**: Certain colours may fade in light - - Always advise customers about care requirements for treated gems. + Always advise clients about care requirements for treated gems. - title: Laboratory Report Terminology - content: | - Understanding laboratory report terminology is essential for interpreting treatment - status and communicating accurately. subsections: - title: Treatment Codes table: @@ -266,40 +501,34 @@ sections: rows: - ["N or NTE", "No treatment evidence", "No indication of any treatment"] - ["H", "Heat treatment", "Evidence of heating detected"] - - ["H(a)", "Heat with foreign residue", "Borax or similar flux present"] - - ["H(b) or H(Be)", "Beryllium diffusion", "Lattice diffusion treatment"] + - ["H(a)", "Heat with flux residue / fracture healing", "Borax or similar flux — disclosed separately from plain H"] + - ["H(b) or H(Be)", "Beryllium diffusion", "Lattice diffusion; LA-ICP-MS required"] - ["O(minor)", "Minor oil", "Light oiling; typical for emerald"] - - ["O(moderate)", "Moderate oil", "Moderate enhancement"] - - ["O(significant)", "Significant oil", "Heavy treatment"] + - ["O(moderate)", "Moderate oil", "Moderate enhancement; requires disclosure"] + - ["O(significant)", "Significant oil", "Heavy treatment; strongly impacts clarity"] - ["R", "Resin", "Polymer-filled fractures"] - - ["F", "Filled", "Fracture or cavity filling"] + - ["F", "Filled", "Fracture or cavity filling (glass, resin)"] - ["C", "Coated", "Surface coating present"] + - ["HPHT", "HPHT treatment", "High pressure high temperature colour modification"] - - title: Interpreting Reports + - title: Key Report Phrases content: | - Key phrases on laboratory reports: - - - **"No indication of heat treatment"**: Stone appears unheated - - **"Evidence of heat treatment"**: Heating detected - - **"Filler detected"**: Fracture filling present - - **"Clarity enhanced"**: Treatment improved apparent clarity - - **"Colour possibly enhanced"**: Colour may not be natural - - **"Origin undeterminable"**: Insufficient evidence for origin + - **"No indication of heat treatment"** — stone appears unheated; high commercial value + - **"Lattice diffusion treatment — beryllium present"** — Be-diffusion; not plain heating + - **"Composite ruby"** — glass-filled composite; not a standard ruby report + - **"HPHT Processed"** — diamond colour modified by HPHT treatment + - **"Filler detected"** — fracture filling present; type will be specified - title: Trade Organisation Standards - content: | - Industry organisations establish treatment disclosure standards. subsections: - title: CIBJO Blue Books content: | - CIBJO (World Jewellery Confederation) publishes standardised terminology: - - - **Natural**: Formed in nature without human intervention - - **Treated**: Natural material altered beyond cutting/polishing - - **Synthetic**: Man-made, same properties as natural - - **Imitation**: Any material resembling another + CIBJO (World Jewellery Confederation) requires full disclosure of all treatments: - Full disclosure of treatments is required under CIBJO standards. + - **Natural**: formed in nature without human intervention + - **Treated**: natural material altered beyond cutting/polishing + - **Synthetic**: man-made with same properties as natural + - **Imitation**: any material resembling another - title: AGTA Enhancement Codes table: @@ -314,13 +543,14 @@ sections: - ["D", "Dyeing"] - ["B", "Bleaching"] - ["C", "Coating"] - - ["U", "Diffusion"] + - ["U", "Diffusion (surface or lattice)"] - ["R", "Irradiation"] + - ["HPHT", "High pressure high temperature"] - ["ASBL", "Assembled (composite)"] - title: Disclosure Chain content: | - Treatment information must pass through the supply chain: + Treatment information must pass through the entire supply chain: 1. Treater → dealer (must disclose) 2. Dealer → retailer (must disclose) diff --git a/docs/learn/origin/afghanistan/emerald.yaml b/docs/learn/origin/afghanistan/emerald.yaml new file mode 100644 index 0000000..dd8f670 --- /dev/null +++ b/docs/learn/origin/afghanistan/emerald.yaml @@ -0,0 +1,131 @@ +title: Panjshir Emerald — Afghanistan +description: Hydrothermal-sediment hosted Panjshir emerald; high Fe UV-Vis bands, low Li, three-phase inclusions in black shale context; distinction from Colombian. +order: 3 +category: origin +subcategory: afghanistan +difficulty: advanced +icon: gem +related: + - origin/afghanistan/overview + - origin/pakistan/emerald + - origin/colombia + - origin/zambia + - species/emerald +tags: + - afghanistan + - panjshir + - emerald + - hydrothermal + - sediment-hosted + - origin/afghanistan + +sections: + - title: Introduction + content: | + Panjshir Valley emerald (Parwan/Kapisa Province, Afghanistan) has been mined since + at least the 19th century but gained systematic international attention after the + Soviet withdrawal; Bowersox et al. (1991) provided the first systematic gemological + description. The deposit is hydrothermally hosted in black shales and phyllites — + a sediment-hosted type genetically different from Colombian black-shale (no igneous + proximity) and from ophiolite-hosted Swat emeralds. The Panjshir is one of the few + major emerald sources without associated igneous rocks nearby. + + - title: Geological Setting + content: | + Panjshir emerald genesis: + + - **Host rock**: Hydrothermal veins in black shales and phyllites — the "sediment- + hosted" model; unlike Colombian black-shale type, Panjshir lacks documented + proximal igneous rocks as the Be/Cr source + - **Formation**: Hydrothermal fluids exploited fracture systems in the organic-rich + black shales; the Cr derives from the shale geochemical reservoir; Be from the + same fluid system + - **Location**: Panjshir Valley, a river valley NE of Kabul; the valley was famous + as an anti-Soviet resistance stronghold; production resumed post-1989 + + - title: Appearance and Properties + content: | + Panjshir emerald characteristics: + subsections: + - title: Colour + content: | + - Medium to deep green; highly saturated fine material is available + - "Pronounced iron-related bands" in UV-Vis spectroscopy characterise Afghan + emeralds and distinguish them from Colombian (Fe-poor) material + - Fluorescence: Red LWUV (Cr³⁺ dominant) but intensity varies with Fe content; + lower than Colombian or Sandawana due to Fe quenching + + - title: Chromophores + content: | + - Cr³⁺ (primary); some V³⁺; Fe (as chromophore and fluorescence quencher) + - The Fe spectral bands are a key analytical criterion — much stronger than + in Colombian material + + - title: Trace Element Chemistry + content: | + Chemical fingerprinting for Panjshir emerald: + subsections: + - title: Low-Li Signature + content: | + - **Li < 200 ppmw**: Shared with Colombian, Swat (Pakistan), and some Brazilian + deposits; distinguishes from Zambian, Zimbabwean, Ethiopian material which + show higher Li + - This signature reflects a non-pegmatitic heritage + + - title: Separation from Colombian + content: | + - **UV-Vis iron bands**: Panjshir shows "pronounced iron-related bands" + not typical of Colombian emerald, which is Fe-poor and therefore shows + stronger red fluorescence — the UV-Vis spectral difference is a primary + analytical criterion + - **Alkali elements, Sc, Mn, Co, Ni, Zn, Ga**: Multivariate trace element + patterns provide further discrimination; laboratory LA-ICP-MS required + - **Three-phase vs Colombian three-phase**: Both have three-phase inclusions + but Colombian includes diagnostic halite cubes and parisite; Panjshir + lacks both of these + + - title: Diagnostic Inclusions + content: | + Panjshir inclusion suite: + + - **Three-phase fluid inclusions**: Reported in Panjshir emeralds; less consistently + documented than in Colombian material; the nature of the trapped solid phases + differs (no halite cubes; no parisite) + - **Carbon-rich black particles**: From the black shale host (carbonaceous matter) + - **Two-phase inclusions**: Liquid + gas; common + - **Absence of parisite**: This Ca-rare earth fluorocarbonate crystal is specific + to Colombian (Muzo-type) material; its absence helps exclude Colombian origin + + - title: Inclusion Comparison + table: + headers: + - Feature + - Panjshir (Afghanistan) + - Colombian Muzo + - Swat (Pakistan) + rows: + - ["Three-phase inclusions", "Present (varies)", "Yes — with halite cube", "Yes (documented)"] + - ["Parisite crystals", "Absent", "Diagnostic — present", "Absent"] + - ["Host context clues", "Black shale carbon", "Albite + calcite", "Chromian muscovite"] + - ["Fe bands in UV-Vis", "Pronounced", "Absent/minimal", "Moderate"] + - ["Li content", "<200 ppmw", "<200 ppmw", "<200 ppmw"] + - ["Fluorescence", "Moderate (Fe quenches)", "Strong (low Fe)", "Strong (high Cr)"] + + - title: Mining and Market + content: | + Panjshir in the trade: + + - Operated by various factions during conflict periods; gem sector rehabilitation + is ongoing + - Afghan emeralds appear regularly on the international market; laboratory + certification is increasingly sought for high-value stones + - Panjshir does not command the Colombian premium in the market; pricing + reflects Afghanistan's lower trade reputation and security concerns + +sources: + - doi: "10.5741/gems.27.1.26" + citation: "Bowersox et al. (1991) Emeralds of the Panjshir Valley, Afghanistan. Gems & Gemology." + - doi: "10.3390/min9090561" + citation: "Karampelas et al. (2019) Emeralds from the Most Important Occurrences: Chemical and Spectroscopic Data. Minerals." + - doi: "10.5741/gems.55.4.614" + citation: "Saeseaw et al. (2019) Geographic Origin Determination of Emerald. Gems & Gemology." diff --git a/docs/learn/origin/afghanistan/lapis.yaml b/docs/learn/origin/afghanistan/lapis.yaml new file mode 100644 index 0000000..62a6825 --- /dev/null +++ b/docs/learn/origin/afghanistan/lapis.yaml @@ -0,0 +1,127 @@ +title: Lapis Lazuli — Sar-e-Sang, Afghanistan +description: Sar-e-Sang (Badakhshan) lapis lazuli — the canonical ancient-world source, >7,000 years of continuous mining, geochemical fingerprinting, grades and quality. +order: 2 +category: origin +subcategory: afghanistan +difficulty: intermediate +icon: gem +related: + - origin/afghanistan/overview + - origin/tajikistan + - species/lapis-lazuli +tags: + - afghanistan + - sar-e-sang + - badakhshan + - lapis-lazuli + - lazurite + - origin/afghanistan + +sections: + - title: Introduction + content: | + The Sar-e-Sang deposit in the Kokcha River Valley of Badakhshan Province, Afghanistan, + is the world's oldest continuously operated gem mine — mined for more than 7,000 years + without interruption. It supplied lapis lazuli to the pharaohs of Egypt, the scribes + of Mesopotamia, and the craftspeople of the Indus Valley civilisation. Lo Giudice et al. + (2016) demonstrated through geochemical provenance protocols that ancient artefacts + from Egyptian museums were of "Afghan origin" — confirming the singular historical + primacy of this deposit. + + - title: Mineralogy of Lapis Lazuli + content: | + Lapis lazuli is a rock, not a single mineral: + subsections: + - title: Principal Minerals + content: | + - **Lazurite**: The blue feldspathoid mineral responsible for the colour; + a member of the sodalite group containing sulfur as S₃⁻ chromophore + - **Calcite**: White to colourless; determines the grade (less calcite = higher + grade in the Sar-e-Sang system) + - **Pyrite**: Gold metallic flecks — characteristic and commercially valued + in Afghan material + - **Minor minerals**: Diopside, phlogopite, wollastonite from the contact + metamorphic environment + + - title: Colour Mechanism + content: | + - The blue colour arises from the S₃⁻ radical anion (trisulfide) in the + lazurite structure — the same mechanism responsible for ultramarine pigment + produced synthetically since the 19th century + - Cu/Fe ratio in the broader mineral assemblage and S₃⁻ concentration control + the exact tone: deeper blue with higher S₃⁻ + + - title: Geochemical Provenance Fingerprinting + content: | + Afghan vs other lapis lazuli sources: + + - Lo Giudice et al. (2016) developed a provenance protocol based on trace element + geochemistry and sulfur isotopes to distinguish Sar-e-Sang material from + Chilean and other sources + - **Sulfur isotopes (δ³⁴S)**: Afghan material has a characteristic isotopic range + distinct from Chilean lapis; this is the primary analytical criterion for + archaeological provenance studies + - **Trace element profile**: LA-ICP-MS fingerprinting of the lazurite and associated + minerals provides additional discrimination + + - title: Quality Grades + table: + headers: + - Grade Name + - Appearance + - Quality + rows: + - ["Sara (Sar)", "Deep ultramarine blue; minimal calcite; uniform", "Highest"] + - ["Surkh", "Medium blue; some calcite veining", "Mid-grade"] + - ["Asmani", "Pale blue; heavy white calcite matrix", "Lower"] + + - title: Pyrite Flecks + callout: + type: info + title: The Gold Flecks + text: | + The gold-coloured metallic flecks in lapis lazuli are PYRITE (FeS₂) — iron + sulfide. In Afghan Sar-e-Sang material, evenly distributed fine pyrite flecks + are considered a quality feature, indicating a natural, untreated stone from + the metamorphic contact zone. + + Heavy calcite mottling WITHOUT pyrite can indicate Chilean material (Ovalle deposit), + which typically shows coarser white patches and less even blue distribution compared + to fine Afghan lapis. + + - title: Distinction from Chilean Lapis + content: | + Trade-level comparison: + + - **Afghan (Sar-e-Sang)**: Deep, even ultramarine blue; characteristic pyrite; + less calcite mottling in fine grades; richer, more saturated colour overall + - **Chilean (Ovalle deposit, Coquimbo)**: Typically more white calcite patches; + more mottled appearance; colour slightly lighter or more patchy + - **Geochemical discrimination**: Sulfur isotopes and trace element profiles + can distinguish sources analytically; trade-level visual assessment is less reliable + + - title: Treatment Concerns + content: | + Common treatments to know: + + - **Dyeing**: Poor-quality lapis is commonly dyed deep blue with organic or + inorganic dyes; detected by cotton swab test (dye bleeds) or FTIR/UV examination + - **Wax impregnation**: Stabilises porous or friable material; FTIR detection + - **Sodalite and lazurite simulants**: "Afghan lapis" may include material from + secondary sources with lower lazurite content; certified provenance adds value + + - title: Historical Significance + content: | + The oldest gem provenance in the world: + + - Lapis lazuli from Sar-e-Sang was found in Egyptian jewellery from 5,000 BCE + - The vivid ultramarine blue of medieval European paintings was ground from + Sar-e-Sang lapis imported via the Silk Road + - The Sanskrit word for blue (nila) and the Persian word for lapis (lazhward) + both derive from the cultural centrality of this material + - The mine has been operated under continuous human control for 70+ centuries — + arguably the longest-operating mine in human history + +sources: + - doi: "10.1007/s12520-016-0430-0" + citation: "Lo Giudice et al. (2016) Protocol for lapis lazuli provenance determination: evidence for Afghan origin. Archaeological and Anthropological Sciences." diff --git a/docs/learn/origin/afghanistan/overview.yaml b/docs/learn/origin/afghanistan/overview.yaml new file mode 100644 index 0000000..c0fa2c5 --- /dev/null +++ b/docs/learn/origin/afghanistan/overview.yaml @@ -0,0 +1,99 @@ +title: Afghanistan — Gem Origins Overview +description: Hindu Kush gem province — lapis lazuli (Sar-e-Sang), Panjshir emerald, Nuristan kunzite; multiple geological settings; conflict and artisanal mining context. +order: 1 +category: origin +subcategory: afghanistan +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/afghanistan/lapis + - origin/afghanistan/emerald + - origin/tajikistan + - origin/pakistan/overview +tags: + - afghanistan + - sar-e-sang + - panjshir + - badakhshan + - nuristan + - lapis-lazuli + - emerald + - origin/afghanistan + +sections: + - title: Introduction + content: | + Afghanistan sits at the convergence of the Hindu Kush, Pamir, and Karakoram ranges + and hosts some of the world's most historically significant gem deposits. The Sar-e-Sang + lapis lazuli mines in Badakhshan are the canonical ancient-world lapis source — mined + continuously for more than 7,000 years and supplying Egypt, Mesopotamia, and the + Indus Valley civilisations. Panjshir Valley emerald and Nuristan kunzite complete + a portfolio that makes Afghanistan a geologically extraordinary gem province. + + - title: Geological Settings + table: + headers: + - Region + - Geological Setting + - Principal Gems + rows: + - ["Sar-e-Sang, Badakhshan", "Contact-metasomatic marble (ancient plutonic belt)", "Lapis lazuli"] + - ["Panjshir Valley", "Hydrothermal veins in black shales/phyllites", "Emerald"] + - ["Jagdalak, Kabul Province", "Marble-hosted corundum", "Ruby [CITATION NEEDED — see note]"] + - ["Nuristan / Kunar", "LCT granite pegmatites", "Kunzite, tourmaline, aquamarine"] + + - title: Mining Under Conflict + callout: + type: warning + title: Four Decades of Disruption + text: | + Afghan gem mining has been severely disrupted by successive conflicts: the Soviet + invasion (1979), civil war (1992–1996), Taliban era (1996–2001), and post-2001 + insurgency. Artisanal mining continued throughout under the control of various + armed groups. + + The gem sector has been a priority for development efforts, but progress is + fragmented. International gem laboratories increasingly receive Afghan-origin + material for origin certification, requiring careful chain-of-custody documentation. + + - title: Nuristan — Kunzite and Pegmatite Gems + content: | + Nuristan Province and adjacent Kunar Province host one of the world's finest + sources of gem kunzite (pink-lilac spodumene, LiAlSi₂O₆, Mn-coloured) in + LCT-type granitic pegmatites. Additional pegmatite gems include: + + - Green tourmaline (elbaite) + - Aquamarine (blue-green beryl) + - Rubellite (red tourmaline) + - Hiddenite (green spodumene — rare) + + Afghan kunzite crystals are among the largest and most saturated in the trade. + No dedicated origin-determination paper for Nuristan kunzite specifically was + retrieved; this material is identified by physical properties and geological provenance. + + - title: Jagdalak Ruby — Citation Note + callout: + type: warning + title: CITATION NEEDED + text: | + Jagdalak (Kabul Province) is noted in geological literature as a marble-hosted + ruby locality related to the Hunza/Mogok marble-ruby belt. However, no dedicated + peer-reviewed gemmological characterisation paper for Jagdalak ruby was retrieved. + The marble-hosted chemistry is inferred from the general Asian marble ruby group + literature (Giuliani et al. 2015). + + This locality is not described in detail here pending dedicated literature. + Builders and FGA candidates should note that Jagdalak ruby origin determination + would rely on the general marble-hosted ruby criteria (low Fe, strong fluorescence, + carbonate inclusions) rather than locality-specific diagnostics. + +sources: + - doi: "10.5741/gems.27.1.26" + citation: "Bowersox et al. (1991) Emeralds of the Panjshir Valley, Afghanistan. Gems & Gemology." + - doi: "10.1007/s12520-016-0430-0" + citation: "Lo Giudice et al. (2016) Protocol for lapis lazuli provenance determination: Afghan origin. Archaeological and Anthropological Sciences." + - doi: "10.5741/gems.46.3.188" + citation: "Shigley et al. (2010) Gem Localities of the 2000s. Gems & Gemology." + - doi: "10.1127/ejm/2015/0027-2442" + citation: "Giuliani et al. (2015) Fluid inclusions in ruby from Asian marble deposits. European Journal of Mineralogy." diff --git a/docs/learn/origin/brazil-additional.yaml b/docs/learn/origin/brazil-additional.yaml new file mode 100644 index 0000000..67b0a25 --- /dev/null +++ b/docs/learn/origin/brazil-additional.yaml @@ -0,0 +1,155 @@ +title: Brazil — Imperial Topaz and Emerald Sub-distinctions +description: Ouro Preto imperial topaz (Cr-coloured, strong LWUV fluorescence); Itabira vs Carnaíba emerald distinction (Cr vs V dominant, inclusion differences). Cross-reference brazil/ folder. +order: 7 +category: origin +difficulty: advanced +icon: gem +related: + - origin/brazil/emerald + - origin/brazil/overview + - origin/colombia-mines + - origin/russia/emerald + - species/emerald + - species/topaz +tags: + - brazil + - ouro-preto + - imperial-topaz + - itabira + - carnaiba + - emerald + - topaz + - origin/brazil-additional + +sections: + - title: Introduction + content: | + This file provides additional depth on two Brazilian gem topics not covered in + the existing brazil/ folder files. Cross-reference origin/brazil/emerald for the + broad Brazilian emerald overview; this file adds the Itabira vs Carnaíba distinction. + Imperial topaz from Ouro Preto is covered here as the only Cr-coloured commercial + topaz in Brazil. + + - title: Imperial Topaz — Ouro Preto, Minas Gerais + content: | + The defining Brazilian imperial topaz deposit: + subsections: + - title: Discovery and Setting + content: | + - "Imperial topaz" is a trade name applied exclusively to sherry-yellow to + orange-pink to pink-orange topaz from the **Ouro Preto** area (and surrounding + Antônio Pereira) of Minas Gerais + - Hosted in hydrothermally altered quartzite and sericite schist lenses within + the Ouro Preto greenstone belt (Archaean); topaz crystallises in sub-vertical + veins and pockets associated with fluorite, mica, and quartz + - Da Costa, Sabioni, and Ferreira (2000) characterised the chemistry and + thermal behaviour of Ouro Preto imperial topaz + + - title: Colour and Chromophore + content: | + - **Colour range**: Yellow-orange (sherry), gold, pinkish-orange (peach), + pink-orange, orange-pink; rarely pure pink — a continuous warm spectrum + - **Chromophore**: Cr³⁺ in trace quantities contributes to the colour; colour + centres from natural irradiation may also contribute + - Da Costa et al. (2000) identified chromium-related character; some + debate remains on the relative contribution of Cr vs colour centres; + the pink modifier in the most prized stones is believed Cr-related + [PARTIALLY_SUPPORTED — not fully established in peer-reviewed record] + + - title: Properties + content: | + - **Formula**: Al₂SiO₄(F,OH)₂; orthorhombic; biaxial positive + - **RI**: 1.619–1.627 (α), 1.620–1.628 (β), 1.627–1.636 (γ); + birefringence: 0.008–0.010 + - **SG**: 3.49–3.57; Hardness: 8 (Mohs) + - **Fluorescence (LWUV)**: Strong yellow-orange to orange — one of the + strongest fluorescences of any gem topaz; a key identification aid + - **Absorption**: Weak Cr bands (~630–680 nm) in some stones + + - title: Treatment Note + content: | + - Many Ouro Preto topazes are irradiated and/or heat-treated to enhance or + shift colour; naturally orange (sherry) material without treatment commands + the highest premiums + - The strong natural LWUV orange fluorescence distinguishes natural-colour + Ouro Preto material from irradiated blue topaz (no fluorescence) and from + other pink/orange gem species + + - title: Imperial Topaz Identification + table: + headers: + - Gem + - RI + - SG + - DR/SR + - Key Distinction + rows: + - ["Ouro Preto topaz", "1.619–1.636", "3.49–3.57", "DR (biaxial)", "Strong orange LWUV; Cr absorption bands"] + - ["Hessonite garnet", "~1.734–1.745", "~3.57–3.73", "SR (isometric)", "Isotropic; higher RI; treacle inclusions"] + - ["Padparadscha sapphire", "1.762–1.770", "3.99–4.01", "DR (uniaxial)", "Much higher RI/SG; Cr + Fe colouring"] + - ["Spessartite garnet", "~1.790–1.815", "~4.12–4.20", "SR (isometric)", "Isotropic; higher RI; orange from Mn"] + + - title: Brazilian Emerald Sub-distinctions + content: | + Two geologically distinct Brazilian emerald deposit types: + subsections: + - title: Itabira / Nova Era Type (Minas Gerais) + content: | + - **Location**: Nova Era, Itabira, Belém do Cruzeio — all Minas Gerais + - **Geological setting**: Talc-chlorite-carbonate schist at the contact between + Proterozoic quartzites and ultramafic bodies — "schist-belt" type, analogous + to Sandawana (Zimbabwe) and Shakiso (Ethiopia) + - **Chromophore**: Cr³⁺ + moderate V³⁺; low Fe content + - **Colour**: Vivid green; comparable to Sandawana quality but achievable at + larger crystal sizes + - **Inclusions**: Biotite mica, chlorite, talc, tremolite (similar to other + schist-belt deposits) + - **Fluorescence**: Strong red LWUV (Cr dominant, low Fe) + + - title: Carnaíba / Bahia Type (Bahia State) + content: | + - **Location**: Carnaíba and Socotó, Bahia State, northeastern Brazil + - **Geological setting**: Talc-carbonate veins cutting ultramafic rocks of the + Carnaíba ultramafite complex + - **Chromophore**: Predominantly V³⁺ with lower Cr — similar to Colombian + Chivor material in Cr/V profile + - **Fe content**: Slightly higher than Itabira + - **Colour**: Slightly "colder" green than the Cr-dominant Itabira type; + less warm, sometimes more yellowish-green + - **Inclusions**: Talc plates (distinctive — soft, platy; from ultramafic host); + two-phase fluid inclusions; phlogopite + + - title: Itabira vs Carnaíba Comparison + table: + headers: + - Feature + - Itabira / Nova Era + - Carnaíba / Bahia + rows: + - ["Chromophore dominant", "Cr³⁺", "V³⁺"] + - ["Colour tone", "Warmer vivid green", "Cooler, slightly yellowish-green"] + - ["Fe content", "Low", "Slightly higher"] + - ["Diagnostic inclusions", "Biotite, chlorite, tremolite", "Talc plates, phlogopite"] + - ["Geological setting", "Schist-belt at quartzite/ultramafic", "Talc-carbonate in ultramafite"] + - ["LWUV fluorescence", "Strong red", "Moderate red"] + - ["V/Cr ratio", "Lower V/Cr", "Higher V/Cr"] + + - title: Laboratory Separation + content: | + Separating Itabira from Carnaíba: + + - **UV-Vis or EDXRF**: V/Cr ratio provides the primary chemical distinction; + Cr-dominant vs V-dominant colouring is detectable spectroscopically + - **Inclusion suite**: Talc plates (Carnaíba) are diagnostically distinct from + tremolite/biotite (Itabira); visual microscopy assists + - **Distinction from Colombian**: Both Brazilian types show higher Li than + Colombian (<200 ppmw Colombian vs >200 ppmw Brazilian schist-belt types); + no halite-bearing three-phase inclusions + +sources: + - doi: "10.15506/jog.2000.27.3.133" + citation: "Da Costa, Sabioni & Ferreira (2000) Imperial topaz from Ouro Preto, Brazil. Journal of Gemmology." + - doi: "10.3390/min9090561" + citation: "Karampelas et al. (2019) Emeralds from the Most Important Occurrences. Minerals." + - doi: "10.5741/gems.55.4.614" + citation: "Saeseaw et al. (2019) Geographic Origin Determination of Emerald. Gems & Gemology." diff --git a/docs/learn/origin/cambodia.yaml b/docs/learn/origin/cambodia.yaml new file mode 100644 index 0000000..816df71 --- /dev/null +++ b/docs/learn/origin/cambodia.yaml @@ -0,0 +1,124 @@ +title: Cambodia — Pailin Sapphire and Battambang Ruby +description: Cambodian gem deposits from Pailin (basaltic sapphire and ruby) and Battambang (marble-hosted ruby); Khmer Rouge era hiatus; distinction from Thai material. +order: 10 +category: origin +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/thailand/ruby + - origin/thailand/sapphire + - origin/burma/ruby + - species/corundum +tags: + - cambodia + - pailin + - battambang + - sapphire + - ruby + - basaltic + - origin/cambodia + +sections: + - title: Introduction + content: | + Cambodia produces two geologically distinct types of corundum: basaltic sapphire + and ruby from Pailin Province (northwestern Cambodia), and small-scale marble-hosted + ruby from the Battambang area. The Pailin field sits in the same Southeast Asian + alkali basalt province as Thailand's Chanthaburi-Trat deposits, just across the + border. Production was severely disrupted during the Khmer Rouge era (1975–1979) + and the subsequent civil conflict, interrupting supply for two decades. + + - title: Geological Settings + content: | + Two corundum-forming environments in Cambodia: + subsections: + - title: Pailin — Basaltic Province + content: | + - Cenozoic intraplate alkali basalt field; same Southeast Asian province as + Chanthaburi-Trat (Thailand) and Ratanakiri (also Cambodia, for zircon) + - Corundum transported to surface in basalt; concentrated in alluvial placers + - High-Fe, low-Cr geochemical environment — same signature as Thai basaltic material + - Adjacent to Bo Rai (Thailand); material from both sides historically mixed + + - title: Battambang — Marble-Hosted Ruby + content: | + - Small-scale occurrence of marble-hosted ruby — geologically analogous to + Mogok and Vietnam marble-type deposits + - Low-Fe environment; strong fluorescence expected + - Much smaller production volume than Pailin + - Geologically distinct from the Pailin basaltic deposits + + - title: Khmer Rouge Era Hiatus + callout: + type: warning + title: Conflict and Gem Production + text: | + The Pailin gem field lay within a Khmer Rouge-controlled zone from 1975 through + the 1990s, effectively halting international trade access for over two decades. + Production resumed after the end of conflict in the early 2000s but at lower + intensity than during the peak 1970s activity. + + Pailin's gem trade was historically significant as a Khmer Rouge revenue source; + ethical sourcing considerations applied to Cambodian gems through the 1990s. + + - title: Pailin Sapphire and Ruby — Diagnostic Features + content: | + Characteristics of Pailin basaltic corundum: + subsections: + - title: Colour + content: | + - **Sapphire**: Blue to green, yellow, and parti-colour; broad range typical + of basaltic sapphires + - **Ruby**: Dark red; comparable to Thai basaltic material but with subtle + differences in trace element ratios + + - title: Chemistry and Spectroscopy + content: | + - **High Fe**: Basaltic geochemical profile — >600 ppm Fe typical + - **Strong 450/460/470 nm triplet**: Fe-related absorption in UV-Vis spectra, + similar to Thai material + - **LWUV fluorescence**: Weak; iron quenches chromium signal + - **Oxygen isotopes**: Values consistent with basalt-related corundum + + - title: Inclusions + content: | + - Basalt-suite minerals: zircon (with halos), feldspar, iron oxides (ilmenite) + - Consistent with basaltic parentage — same mineral family as Thai material + - No marble-hosted inclusions (no calcite, apatite, sphene) + + - title: Pailin vs Thai Distinction + content: | + Separating Cambodian Pailin from Chanthaburi-Trat: + + - **Historical difficulty**: Pailin and Bo Rai (Thailand) material was historically + traded together through Chanthaburi and often mixed; laboratory separation was + not routine + - **Modern LA-ICP-MS**: Trace element ratio patterns (Ga/Mg, Fe/Ti, Cr/Ga) and + oxygen isotope analysis can discriminate Pailin from Chanthaburi with some + confidence; the separation is a laboratory-level task + - **Practical trade note**: Material described as "Thai ruby" in the trade may + include Cambodian origin stone heated in Thailand + + - title: Battambang Ruby Distinction + callout: + type: info + title: Marble-Hosted in a Basaltic Province + text: | + The Battambang marble-hosted ruby occurrence is geologically anomalous in a + province dominated by basaltic deposits. Marble-hosted ruby characteristics + (low Fe, strong fluorescence, calcite inclusions) apply — similar in principle + to Vietnamese marble ruby from Luc Yen, though at much smaller production scale. + + If marble-type inclusions are identified in a Cambodian-provenance ruby, Battambang + origin should be considered. + +sources: + - doi: "10.5741/gems.18.4.186" + citation: "Keller (1982) The Chanthaburi-Trat Gem Field, Thailand. Gems & Gemology." + - doi: "10.5741/gems.55.4.536" + citation: "Palke et al. (2019) Geographic Origin Determination of Blue Sapphire. Gems & Gemology." + - doi: "10.5741/gems.45.4.236" + citation: "Shor & Weldon (2009) Ruby and Sapphire Production and Distribution. Gems & Gemology." + - doi: "10.1127/ejm/2015/0027-2442" + citation: "Giuliani et al. (2015) Fluid inclusions in ruby from Asian marble deposits. European Journal of Mineralogy." diff --git a/docs/learn/origin/colombia-mines.yaml b/docs/learn/origin/colombia-mines.yaml new file mode 100644 index 0000000..86092d3 --- /dev/null +++ b/docs/learn/origin/colombia-mines.yaml @@ -0,0 +1,197 @@ +title: Colombian Emerald Mines — Sub-Distinctions +description: Mine-level diagnostics for Muzo (parisite + halite), Chivor (pyrite dominant), Coscuez, La Pita, and trapiche emerald; cross-reference to colombia.yaml. +order: 6 +category: origin +difficulty: advanced +icon: gem +related: + - origin/colombia + - origin/zambia + - origin/afghanistan/emerald + - species/emerald +tags: + - colombia + - muzo + - chivor + - coscuez + - trapiche + - emerald + - three-phase + - parisite + - pyrite + - origin/colombia-mines + +sections: + - title: Introduction + content: | + This file provides mine-level sub-distinctions for Colombian emerald beyond the + origin-level overview in colombia.yaml. All Colombian deposits share the + "black shale" or sedimentary-hosted hydrothermal model: Cretaceous black shales + (Villeta Formation) host emerald-forming brines without associated igneous rocks. + All three major mines share the diagnostic Colombian three-phase inclusion (liquid + + gas + halite cube) — the halite being unique to Colombian emerald worldwide. The + mine-level distinctions below allow laboratory sub-classification. + + - title: Colombian Deposit Type — The Black Shale Model + content: | + All Colombian mines share these features: + + - **Host rock**: Hydrothermal veins in Cretaceous black shales/phyllites; no + nearby igneous rocks — purely sediment-hosted + - **Brine**: NaCl-saturated hydrothermal fluid at ~300°C in a thrust-belt setting + - **Three-phase inclusions**: Liquid + gas + halite (NaCl) cube — the halite is + the critical discriminator from ALL other emerald origins worldwide; no other + major source traps NaCl cubes in three-phase inclusions + - **Chromophore**: Cr³⁺ ± V³⁺; ratio varies by mine; affects colour tone + - **Li content**: <200 ppmw — shared with Afghan and Pakistani emerald + + - title: Muzo Mine + content: | + The most famous Colombian mine: + subsections: + - title: Location and Geology + content: | + - Boyacá Department, ~165 km north of Bogotá + - Primary mine of the "Western Zone" of Colombian emerald production + - Same black shale hydrothermal system as Coscuez/La Pita + + - title: Chromophore Profile + content: | + - Higher **Cr** relative to V — "warmer" green, typically a pure vivid + medium green; often the most valued pure green Colombian colour + + - title: Diagnostic Inclusions + content: | + - **Three-phase inclusions**: Liquid + gas + halite (NaCl) cube — as all + Colombian + - **Parisite**: Calcium rare-earth fluorocarbonate; yellow-orange hexagonal + crystals; highly diagnostic for Muzo specifically — absent in Chivor + - **Albite**: White platy crystals + - **Calcite rhombs** + - **Pyrite**: Present but less abundant than Chivor + - **Jagged, irregular growth tubes** + - Vasquez and Zellagui (2019) noted the pyrite and chromite inclusion assemblage + differentiates Colombian mine sources + + - title: Chivor Mine + content: | + The "Eastern Zone" mine with distinct character: + subsections: + - title: Location and History + content: | + - Boyacá Department, ~100 km northeast of Bogotá + - Known to pre-Columbian Muisca people; rediscovered 1904 by Reinaldo Uribe + - Schmetzer, Martayan, and Ortiz (2020) published the comprehensive history + + - title: Chromophore Profile + content: | + - Generally **higher V relative to Cr** than Muzo — cooler, often bluish-green + to teal at lower saturations; sometimes described as more "electric" blue-green + + - title: Diagnostic Inclusions + content: | + - **Three-phase inclusions**: Liquid + gas + halite (same diagnostic as all Colombian) + - **Pyrite**: Cubic metallic inclusions — far more abundant and larger at Chivor + than at Muzo; THIS IS THE MOST RELIABLE VISUAL MINE-LEVEL DISTINCTION + - **Albite** crystals (white platy) + - **Calcite** and dolomite + - Often cleaner overall (fewer total inclusions per stone) + - **NO PARISITE**: Parisite is Muzo-specific; its absence helps exclude Muzo + + - title: The Chivor vs Muzo Visual Rule + callout: + type: tip + title: The Mine Diagnostic in One Line + text: | + CHIVOR = abundant pyrite cubes + cool blue-green colour + no parisite + + MUZO = parisite (yellow-orange hexagonal crystals) + warm pure green + less pyrite + + Both have the three-phase liquid + gas + halite inclusion (all Colombian); the + mine-level distinction rests on (1) parisite presence/absence and (2) pyrite + abundance. + + - title: Coscuez Mine + content: | + The third major traditional mine: + + - Location: Boyacá Department, near Muzo; same geological zone + - Shares the Muzo-type inclusion suite: three-phase + parisite + albite; same + black shale host and hydrothermal system + - Much commercial Colombian emerald from the 1970s–1990s originated from Coscuez + without separate attribution from Muzo; the two are often grouped as "Western Zone" + - **Trapiche emerald** was first associated with Coscuez and the adjacent Peñas + Blancas area + + - title: Newer Mines — La Pita, La Pava, Cunas + content: | + Post-1990s mining in Boyacá Department: + + - **La Pita** (Coscuez extension area), **La Pava** (Muzo-Quípama area), + **Cunas** (Muzo area) + - These mines produce commercially but share the Muzo-zone inclusion suite + (three-phase + parisite ± calcite) + - Sub-geographic discrimination between Muzo, Coscuez, La Pita, and Cunas is + beyond current routine laboratory capability + - Most labs report "Colombian" or "Western Zone" (Muzo-type) vs "Eastern Zone" + (Chivor-type); finer mine-level attribution is not routinely certified + + - title: Trapiche Emerald + content: | + A uniquely Colombian growth phenomenon: + subsections: + - title: What Is Trapiche? + content: | + - Trapiche emerald is NOT a variety of emerald but a **growth pattern**: + a six-spoke, wheel-like pattern visible in cross-section perpendicular to + the c-axis, named after the Spanish word for a sugar-mill cogwheel + - O'Donoghue (1971) first described this in the Journal of Gemmology: + "Trapiche Emerald" + - Sun, Gao, and Deng (2023) documented a rare "'Star of David' Pattern + Produced by a Trapiche Emerald from Colombia" — a geometric variant + + - title: Formation Mechanism + content: | + - Six emerald growth sectors form (reflecting the hexagonal crystal structure) + - Inter-sector boundaries are infiltrated by organic matter (bitumen), albite, + and calcite during crystal growth interruptions + - The dark "spokes" are inclusion-rich inter-sector zones; the emerald blades + are the six growth sectors + - Best seen as a cross-section parallel to the basal plane (perpendicular to c) + + - title: Occurrence + content: | + - Primarily Coscuez and Peñas Blancas zones — NOT from Chivor + - Exceptional rarity: strong collector premium + - Distinguished from trapiche ruby (Myanmar; different genesis) and + trapiche sapphire (very rare) + - The host emerald in trapiche material has Muzo-type properties (Cr-dominant, + three-phase inclusions in the emerald sectors; parisite possible) + + - title: Mine Comparison Table + table: + headers: + - Feature + - Muzo + - Chivor + - Coscuez + rows: + - ["Zone", "Western", "Eastern", "Western"] + - ["Chromophore", "Cr dominant", "V > Cr", "Cr dominant (like Muzo)"] + - ["Colour tone", "Warm pure green", "Cooler blue-green", "Similar to Muzo"] + - ["Parisite", "YES — diagnostic", "ABSENT", "Present (like Muzo)"] + - ["Pyrite", "Minor", "Abundant — diagnostic", "Present"] + - ["Three-phase halite", "YES (all Colombian)", "YES (all Colombian)", "YES (all Colombian)"] + - ["Trapiche association", "No", "No", "YES (Coscuez + Peñas Blancas)"] + +sources: + - doi: "10.15506/jog.2019.36.8.687" + citation: "Vasquez & Zellagui (2019) Pyrite and chromite inclusions in Colombian emerald. Journal of Gemmology." + - doi: "10.5741/gems.56.1.66" + citation: "Schmetzer, Martayan & Ortiz (2020) History of the Chivor Emerald Mine. Gems & Gemology." + - doi: "10.15506/jog.1971.12.8.329" + citation: "O'Donoghue (1971) Trapiche Emerald. Journal of Gemmology." + - doi: "10.15506/jog.2023.38.7.652" + citation: "Sun, Gao & Deng (2023) 'Star of David' Pattern Produced by a Trapiche Emerald. Journal of Gemmology." + - doi: "10.3390/min9090561" + citation: "Karampelas et al. (2019) Emeralds from the Most Important Occurrences. Minerals." diff --git a/docs/learn/origin/ethiopia.yaml b/docs/learn/origin/ethiopia.yaml new file mode 100644 index 0000000..bdeafed --- /dev/null +++ b/docs/learn/origin/ethiopia.yaml @@ -0,0 +1,183 @@ +title: Ethiopia — Wollo Opal and Shakiso Emerald +description: Wollo (Welo) hydrophane opal — volcanic host, water-absorbing, distinct from Australian; Shakiso mica-schist emerald; Tigray sapphire [CITATION NEEDED]. +order: 22 +category: origin +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/australia/black-opal + - origin/australia/white-opal + - origin/zambia + - origin/zimbabwe + - species/emerald + - species/opal +tags: + - ethiopia + - wollo + - welo + - opal + - hydrophane + - shakiso + - emerald + - volcanic + - origin/ethiopia + +sections: + - title: Introduction + content: | + Ethiopia has emerged as a major gem-producing country with two internationally + significant deposits: Wollo (Welo) opal — discovered 2008, characterised 2010 — + which challenged the assumption that gem opal was primarily Australian; and Shakiso + emerald (Guji Zone, southern Ethiopia) — discovered around 2016 and immediately + noted for fine colour. Ethiopia's gem geology reflects both Cenozoic volcanic + activity (opal) and Pan-African metamorphic basement (emerald). + + - title: Wollo (Welo) Opal — Discovery and Geology + content: | + The Ethiopian opal revolution: + subsections: + - title: Discovery + content: | + - Play-of-colour opal from the Wollo Province (specifically near Wegel Tena) + first reported to scientific literature in 2010 + - Rondeau et al. (2010) provided the foundational study: "Play-of-Color Opal + from Wegel Tena, Wollo Province, Ethiopia" — API-confirmed [VERIFIED] + - The study established deposit characteristics and began scientific distinction + from Australian opal + + - title: Geological Host + content: | + - Hosted in **Tertiary volcanic rocks** (rhyolitic ignimbrites and silicic flows) + of the Ethiopian highlands + - Late-stage silica-rich hydrothermal activity associated with the volcanic + sequence deposited amorphous SiO₂·nH₂O in voids and fractures + - Geologically distinct from Australian opal: Australia is sedimentary + (Cretaceous marine sediments); Ethiopia is volcanic (Tertiary rhyolite) + + - title: Hydrophane — The Critical Diagnostic + content: | + The defining property of Ethiopian opal: + subsections: + - title: What Is Hydrophane? + content: | + - Ethiopian opal (especially Wollo material) is characteristically **hydrophane** + — it absorbs water, and its optical properties change measurably with hydration + - This porous character results from the volcanic host environment and the + way silica was deposited in the vugs + + - title: Measurable Property Changes + content: | + - **Transparency**: Dry Ethiopian opal is often white/milky to semi-transparent; + upon absorbing water it becomes more transparent and play of colour intensifies + - **RI**: Increases measurably as water is absorbed (~1.37 dry → ~1.42 when wet) + - **Weight**: Increases measurably when wet (3–10% weight gain in <1 hour) + - **SG**: Appears different when measured wet vs dry — hydrostatic SG measurement + should NOT be performed on hydrophane opal + - **Play of colour**: May change direction or intensity with hydration state + + - title: Reversible Colour Change with Humidity + content: | + - A subset of Wollo stones shows a reversible change in appearance linked to + ambient humidity — more vivid/transparent in humid conditions, more milky + in dry conditions + - This is a physical property change (water content), NOT a gem-quality optical + colour change (such as the alexandrite effect) + - Must not be described as "alexandrite-effect" or "colour change" in the + gemmological sense; it is hydration-state-dependent transparency variation + + - title: Practical Hydrophane Consequences + callout: + type: warning + title: Treatment Absorption Risk + text: | + Hydrophane porosity creates a significant vulnerability: treatments (dyes, smoke + blackening, sugar-acid carbonisation) can be absorbed into the opal when wet. + + - SMOKE TREATMENT: Exposing wet hydrophane opal to smoke deposits carbon + particles that darken the body tone, simulating black opal — partially reversible + - DYE IMPREGNATION: Wet opal absorbs dye solutions; detection by FTIR or + UV examination + - CLEANING: Ethiopian opal should NOT be cleaned ultrasonically or left in water + for extended periods + + Australian boulder opal is not hydrophane and is not susceptible to these treatments. + + - title: Ethiopian vs Australian Opal + table: + headers: + - Property + - Welo (Ethiopian) + - Australian (Coober Pedy/Lightning Ridge) + rows: + - ["Host rock", "Tertiary rhyolitic volcanic tuff", "Cretaceous marine sediments"] + - ["Hydrophane", "Yes — typically strong", "No (non-porous in boulder opal)"] + - ["RI (dry)", "~1.37", "~1.42–1.43"] + - ["SG", "~1.95–2.05 (varies with hydration)", "~2.05–2.10 (more stable)"] + - ["Body tone", "White to crystal (transparent when wet)", "White (Coober Pedy); dark (Lightning Ridge black)"] + - ["Treatment risk", "High (absorbs treatments when wet)", "Lower"] + - ["Play of colour", "Often strong, broad patches", "Variable; Lightning Ridge vivid black opal"] + + - title: Shakiso Emerald + content: | + Pan-African mica-schist hosted emerald from southern Ethiopia: + subsections: + - title: Discovery and Geology + content: | + - Halo-Shakiso district, Guji Zone, Oromia Region; brought to commercial + attention approximately 2016 + - Hosted in **Pan-African mica schist** cut by quartz-carbonate veins at + the contact between mica schist and **serpentinised peridotite** (ultramafic) + - Genesis analogous to Sandawana (Zimbabwe) and Ural (Russia): schist-belt type + - Nicol et al. (2022) confirmed P-T conditions: ~1.5–3 kbar and 300–430°C; + NaCl-dominated saline brine + CO₂-bearing fluids + + - title: Properties and Comparison + content: | + - **Chromophores**: Cr³⁺ + V³⁺; similar Cr/V profile to Ural and Sandawana; + differs from high-V Brazilian Itabira and low-Cr/high-V Zambian material + - **Fe content**: Low — contributes to good colour purity and moderate-strong + red LWUV fluorescence + - **Inclusions**: Phlogopite mica (more than Sandawana); tremolite needles; + chlorite; two-phase fluid inclusions; apatite + - **Size**: Small to medium; fine stones >1 ct less common but available + - **Chelsea Colour Filter**: Red (Cr dominant) + + - title: Shakiso Comparison + table: + headers: + - Property + - Shakiso (Ethiopia) + - Sandawana (Zimbabwe) + - Ural (Russia) + rows: + - ["Chromophore", "Cr + V", "Cr dominant", "Cr + V"] + - ["Fe content", "Low", "Very low", "Low"] + - ["Mica inclusion", "Phlogopite (abundant)", "Less mica", "Phlogopite (abundant)"] + - ["Tremolite", "Present", "Present (diagnostic)", "Less common"] + - ["Crystal size", "Small–medium", "Very small", "Medium–large"] + - ["LWUV fluorescence", "Moderate–strong red", "Very strong red", "Moderate–strong red"] + + - title: Tigray Sapphire — Citation Note + callout: + type: warning + title: CITATION NEEDED — Tigray Sapphire + text: | + Corundum (sapphire) finds in the Tigray Region (northern Ethiopia) have been + reported intermittently. These appear to be high-Fe basalt-hosted sapphires + associated with Cenozoic alkalic volcanism — consistent with the high-Fe basaltic + sapphire family (Thailand, Cambodia, eastern Australia), tending toward dark, + steely blue with weak fluorescence. + + However, no peer-reviewed gemmological characterisation paper was retrieved for + Tigray sapphire — this locality is [CITATION NEEDED] / [UNVERIFIED] per + VERIFIED.md (D-01). Specific gemmological diagnostics cannot be stated as fact; + this note flags the gap for a targeted research pass. + +sources: + - doi: "10.5741/gems.46.2.90" + citation: "Rondeau et al. (2010) Play-of-Color Opal from Wegel Tena, Wollo Province, Ethiopia. Gems & Gemology. [VERIFIED]" + - doi: "10.3749/canmin.2000069" + citation: "Nicol et al. (2022) Pressure-temperature-fluid constraints for Halo-Shakiso Emerald Deposit, Ethiopia. The Canadian Mineralogist." + - doi: "10.3390/min9090561" + citation: "Karampelas et al. (2019) Emeralds from the Most Important Occurrences. Minerals." diff --git a/docs/learn/origin/india.yaml b/docs/learn/origin/india.yaml new file mode 100644 index 0000000..657fd11 --- /dev/null +++ b/docs/learn/origin/india.yaml @@ -0,0 +1,146 @@ +title: India — Alexandrite, Diamond (Panna), and Garnet +description: Indian gem deposits — Andhra Pradesh alexandrite and chrysoberyl, Panna kimberlite diamond, Orissa garnet; geological context; Koh-i-Noor attribution qualified. +order: 13 +category: origin +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/ceylon + - origin/kashmir + - species/corundum + - species/chrysoberyl +tags: + - india + - andhra-pradesh + - panna + - orissa + - alexandrite + - diamond + - kimberlite + - origin/india + +sections: + - title: Introduction + content: | + India's gem deposits reflect the country's diverse Precambrian and Proterozoic + geology. Significant production areas include Andhra Pradesh (chrysoberyl and + alexandrite in Eastern Ghats pegmatites), Madhya Pradesh (diamond in Panna + kimberlites), and Orissa (garnet). Kashmir sapphire, though commercially exhausted, + remains India's most famous gem locality and is covered separately. + + - title: Geological Settings + table: + headers: + - Region + - Province + - Geological Setting + - Gems + rows: + - ["Visakhapatnam / East Godavari", "Andhra Pradesh", "Acidic pegmatites in Eastern Ghats khondalites", "Chrysoberyl, alexandrite"] + - ["Panna District", "Madhya Pradesh", "Majhgawan and Hinota kimberlite pipes (~1100 Ma)", "Diamond"] + - ["Orissa (Odisha)", "Various districts", "Archaean basement; Precambrian metamorphic rocks", "Pyrope and almandine garnet"] + - ["Tamil Nadu", "Southern India", "Garnet-bearing metamorphic basement", "Star garnet (almandine-pyrope)"] + + - title: Alexandrite — Andhra Pradesh + content: | + Eastern Ghats chrysoberyl and alexandrite: + subsections: + - title: Geological Context + content: | + - Chrysoberyl (BeAl₂O₄) occurs in acidic pegmatites intruding khondalites + (metamorphic granulites) of the Eastern Ghats mobile belt + - Kasipathi (1996) confirmed: "Chrysoberyl occurs in the acidic pegmatite + intrusive into the khondalite of the Eastern Ghats of north coastal Andhra Pradesh" + - The pegmatite supplies Be and Al; the ultramafic country rock or metamorphic + khondalite supplies Cr for alexandrite variety formation + + - title: Properties + content: | + - Colour change: Green in daylight / red in incandescent (Cr³⁺ in BeAl₂O₄) + - Fluorescence: Red LWUV (Cr³⁺) + - RI: 1.745–1.757 (α), biaxial positive + - SG: ~3.73; Hardness: 8.5 + + - title: Origin Determination Note + content: | + - Indian alexandrite is noted in the trade for its colour-change effect + but fine colour change quality — the definitive balance of green-to-red + response — is generally considered less striking than fine Ural (Russian) + material + - This is a generalisation based on trade consensus: the sourcing literature + does not provide a peer-reviewed comparison of Indian vs Ural quality as + a verified gemmological fact; individual stones vary + + - title: Diamond — Panna District + content: | + India's only significant primary diamond source: + subsections: + - title: Geology + content: | + - Panna Diamond Belt, Madhya Pradesh: kimberlite pipes (Majhgawan and Hinota, + ~1100 Ma) emplaced in the Baghain Sandstone of the Vindhyan Supergroup + - The basement Bundelkhand granitoids underlie the Vindhyan sedimentary cover; + diamonds occur both in the primary kimberlite and in secondary alluvial + and conglomerate deposits derived from kimberlite erosion + - Active mining by NMDC (National Mineral Development Corporation) + + - title: Koh-i-Noor Attribution — Critical Note + content: | + - Various famous diamonds including the Koh-i-Noor, Regent (Pitt Diamond), + and others are traditionally attributed to the alluvial workings of the + Golconda-Panna region of central India + - This attribution is TRADITIONALLY ACKNOWLEDGED in historical and gem trade + literature; it is NOT confirmed by modern gemmological peer-reviewed analysis + - The Rau (2007) paper on the Panna Diamond Belt confirms the geological + framework but does not attribute any specific famous diamond to Panna + - For examination purposes: state that famous historic diamonds including + the Koh-i-Noor are "traditionally attributed to" the Golconda/Panna + alluvial region of India — not that their Indian origin is a confirmed fact + + - title: Koh-i-Noor Qualification + callout: + type: warning + title: VERIFIED.md Flag F-08 — Must Qualify Attribution + text: | + VERIFIED.md explicitly flags (F-08): "Remove or qualify [Koh-i-Noor Panna + attribution] with 'traditionally attributed'; do not present as verified + historical fact." + + The correct statement is: "The Koh-i-Noor diamond is traditionally attributed + to the alluvial gem workings of the Golconda-Panna region of central India." + + Do NOT state: "The Koh-i-Noor was found at Panna" or "The Koh-i-Noor certainly + originates from Golconda" — these statements go beyond what the peer-reviewed + record supports. + + - title: Diamond Origin Determination Caveat + callout: + type: info + title: Individual Diamond Provenance + text: | + Geographic origin determination cannot be performed on individual diamonds + without reference samples and provenance documentation. No diagnostic inclusion + suite or chemical fingerprint uniquely identifies an individual diamond as Indian + rather than, for example, Australian kimberlitic. The Panna geological context + is well-established; attribution of individual historic stones is historical + tradition, not scientific determination. + + - title: Orissa Garnet + content: | + Garnet from Orissa (Odisha): + + - Pyrope and almandine garnet from Proterozoic metamorphic and Archaean basement + of Odisha; artisanal production + - Tamil Nadu produces 4-rayed and 6-rayed star garnet (almandine-pyrope with + rutile asterism inclusions); India is a significant source of star garnet + - No diagnostic origin-determination criteria specific to Indian garnet at the + bench level; provenance documentation required + +sources: + - doi: "10.17491/jgsi/1996/480412" + citation: "Kasipathi (1996) Chrysoberyl from Visakhapatnam and East Godavari Districts, Andhra Pradesh. Journal of the Geological Society of India." + - doi: "10.17491/jgsi/2007/690306" + citation: "Rau (2007) Panna Diamond Belt, Madhya Pradesh — A Critical Review. Journal of the Geological Society of India." + - doi: "10.5741/gems.46.3.188" + citation: "Shigley et al. (2010) Gem Localities of the 2000s. Gems & Gemology." diff --git a/docs/learn/origin/iran.yaml b/docs/learn/origin/iran.yaml new file mode 100644 index 0000000..6b30f90 --- /dev/null +++ b/docs/learn/origin/iran.yaml @@ -0,0 +1,130 @@ +title: Iran — Nishapur (Neyshabur) Turquoise +description: Persian turquoise from Neyshabur, Khorasan — the global colour standard; volcanic tuff host, spider-web matrix, Cu-Al phosphate, treatment assessment. +order: 14 +category: origin +difficulty: intermediate +icon: gem +related: + - origin/overview + - species/turquoise +tags: + - iran + - persia + - nishapur + - neyshabur + - turquoise + - phosphate + - origin/iran + +sections: + - title: Introduction + content: | + Persian turquoise from the Neyshabur (Nishapur) district of Khorasan-e Razavi Province + is historically the most celebrated turquoise in the world — the deposit that defined + the colour "turquoise" as a colour category for Western culture and trade. Production + has continued for at least 2,000 years, making Neyshabur one of the world's longest- + continuously-operating gem sources. Shirdam et al. (2021) provided a comprehensive + review in Gems & Gemology. + + - title: Geological Context + content: | + Neyshabur turquoise deposit geology: + subsections: + - title: Host Rock + content: | + - Turquoise occurs in hydrothermally altered volcanic tuffs and rhyolitic rocks + within the Neyshabur district + - Hydrothermal copper-bearing fluids altered the volcanic host, precipitating + secondary copper-aluminium phosphate (turquoise) in veins, fractures, and + nodules within the altered rhyolite + - The Cu source is the volcanic rock suite itself; Al and P from the alteration + system; the reaction occurs under near-surface, low-temperature conditions + + - title: Formula + content: | + - Turquoise formula: CuAl₆(PO₄)₄(OH)₈·4H₂O + - Colour depends on Cu/Fe ratio: higher Fe shifts colour toward green + - The finest "robah" grade (see below) has the highest Cu relative to Fe + + - title: Quality Grades + table: + headers: + - Grade + - Description + - Quality + rows: + - ["Robah (fox-hole)", "Even sky blue; no matrix; maximum colour saturation", "Highest — rarest"] + - ["Angi (vein)", "Vein material; sky blue; some matrix acceptable", "High"] + - ["Arabi (Arabic)", "Good colour; moderate matrix", "Medium"] + - ["Spider-web", "Matrix-patterned; mid-grade; commercially desirable", "Mid-grade commodity"] + + - title: The Spider-Web Matrix + callout: + type: info + title: A Characteristic and Desirable Feature + text: | + The "spider-web" matrix of Persian turquoise — thin veins of brown limonite + or black manganese oxide running through the turquoise in an irregular network — + is characteristic of Neyshabur material and commercially desirable in mid-grade + pieces. Fine spider-web turquoise with an even blue background and well-defined + matrix commands premium prices in certain markets (Native American-influenced + US market and Middle Eastern markets). + + American Sleeping Beauty turquoise (Arizona) is notably matrix-free and more + even blue — aesthetically different from spider-web Persian material. + + - title: Origin Determination + content: | + Identifying Persian vs other turquoise origins: + subsections: + - title: Analytical Methods + content: | + - **Trace element geochemistry** (LA-ICP-MS or EDXRF): Cu, Al, Fe, Zn ratios; + Persian material has characteristic signatures documented by Shirdam et al. (2021) + - **Raman spectroscopy**: Confirms turquoise mineral species (vs dyed howlite, + magnesite, or stabilised materials) + - **FTIR**: Identifies stabilising resin/wax treatment (phosphate vs polymer + absorption bands) + + - title: Visual Comparison + content: | + - **Persian vs Sleeping Beauty (Arizona)**: Persian more deeply blue, often with + spider-web matrix; Sleeping Beauty pale to medium blue, matrix-free, "cleaner" + - **Persian vs Chinese (Hubei)**: Hubei typically more green-blue, heavier + veining; different Cu/Fe/Zn profile + - Visual comparison is trade-level guidance only; analytical confirmation required + + - title: Treatment — A Critical Issue + callout: + type: warning + title: Most Neyshabur Material Is Stabilised + text: | + Much of the commercial Neyshabur output is STABILISED — impregnated with wax, + resin, or plastic to improve durability, surface finish, and colour. This is + accepted trade practice but reduces value relative to untreated natural turquoise. + + FTIR spectroscopy distinguishes: + - Untreated natural turquoise: Clean phosphate absorption pattern + - Wax-treated: Hydrocarbon C-H stretch bands present + - Resin/polymer treated: Polymer absorption bands present + + "Natural" turquoise without stabilisation is increasingly rare and commands + premium pricing when certified by a laboratory. + + - title: Properties + table: + headers: + - Property + - Value + rows: + - ["Composition", "CuAl₆(PO₄)₄(OH)₈·4H₂O"] + - ["Crystal system", "Triclinic; microcrystalline aggregate"] + - ["Hardness", "5–6 (Mohs); lower in porous material"] + - ["SG", "2.60–2.85"] + - ["RI", "1.61–1.65 (spot reading on curved surface)"] + - ["Fluorescence", "Inert to very weak"] + - ["Lustre", "Waxy to dull; polish improves appearance"] + +sources: + - doi: "10.5741/gems.57.3.240" + citation: "Shirdam et al. (2021) Persian Turquoise: The Ancient Treasure of Neyshabur. Gems & Gemology." diff --git a/docs/learn/origin/mozambique.yaml b/docs/learn/origin/mozambique.yaml new file mode 100644 index 0000000..a8fe713 --- /dev/null +++ b/docs/learn/origin/mozambique.yaml @@ -0,0 +1,195 @@ +title: Mozambique — Montepuez Ruby and Paraíba Tourmaline +description: Montepuez ruby (Cabo Delgado) — two-type amphibolite-hosted and alluvial; Mavuco Paraíba-type Cu-bearing tourmaline; LA-ICP-MS origin discrimination. +order: 20 +category: origin +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/east-africa/ruby + - origin/east-africa/paraiba-type + - origin/burma/ruby + - origin/colombia + - species/corundum + - species/tourmaline +tags: + - mozambique + - montepuez + - cabo-delgado + - ruby + - paraiba-tourmaline + - mavuco + - gemfields + - origin/mozambique + +sections: + - title: Introduction + content: | + Mozambique has emerged since approximately 2009 as the world's largest ruby producer + by volume. The Montepuez deposit in Cabo Delgado Province (northern Mozambique) + is operated by Gemfields PLC and has transformed the global ruby supply. Additionally, + the Mavuco deposit (Nampula Province) is one of the world's major sources of Paraíba- + type copper-bearing elbaite tourmaline. Both deposits are part of the Pan-African + metamorphic basement of Mozambique. + + Note: The east-africa/ files cover Mozambique briefly in the regional context; + this file provides the Mozambique-specific depth. + + - title: Montepuez Ruby — Discovery and Geology + content: | + Montepuez deposit background: + subsections: + - title: Discovery and Operation + content: | + - Discovered approximately 2009; Gemfields PLC commenced commercial production + and began selling rough through sealed-bid auctions in 2014 + - Chapin, Pardieu, and Lucas (2015) documented the initial findings + - Located in the Cabo Delgado nappe complex (northern Mozambique); metamorphic + basement rocks of ~550–630 Ma (East African Orogen) + + - title: Two Genetically Distinct Ruby Types + content: | + - Vertriest and Saeseaw (2019) demonstrated that Montepuez hosts two genetically + and chemically distinct ruby populations; this "two-type" classification is + the key gemmological framework for this deposit + + - title: Type A — Primary (Amphibolite-Hosted) Ruby + content: | + Low-Fe primary ruby from in-situ metamorphic host: + subsections: + - title: Geology + content: | + - Found in situ in amphibolite and marble-amphibolite lithologies; the host + geology is debated — some literature refers to "amphibolite-hosted," others + to serpentinite alteration of the amphibolite + - Metamorphic basement representing exhumed lower crustal rocks + + - title: Chemistry + content: | + - **Low Fe**: Typically Fe < 3,000–5,000 ppm; elevated Cr (>1,000 ppm) and V + - This places Type A Mozambique ruby chemically closer to marble-hosted Mogok + (Burma) than to high-Fe basaltic rubies (Thailand, Cambodia) + - **Challenge**: Some Type A Mozambique rubies OVERLAP with Burmese rubies in + trace element space; Palke et al. (2019) identified this explicitly — origin + discrimination requires multiple overlapping data sets + + - title: Type B — Alluvial (Secondary) Ruby + content: | + Higher-Fe secondary ruby from gravel pockets: + + - Alluvial ruby from adjacent gravel pockets and eluvial concentrations tends + to be HIGHER in Fe + - Chemistry closer to Thai/Cambodian basaltic-type: weaker fluorescence, + darker tone, stronger broad-band Fe absorption + - The two-type system (primary low-Fe vs secondary high-Fe) within one geographic + deposit is a distinctive feature requiring careful analytical assessment + + - title: Inclusion Suite + content: | + Diagnostic inclusions for Montepuez ruby: + subsections: + - title: Mineral Inclusions + content: | + - **Amphibole needles** (hornblende/pargasite): Elongated, greenish-black, + often in clusters — from the amphibolite metamorphic assemblage + - **Apatite crystals**: Rounded to hexagonal prisms — very diagnostic for the + Montepuez metamorphic assemblage + - **Mica (phlogopite/biotite) platelets** + - **Zircon with halos**: Metamict; tension fracture corona + - **Growth tubes** parallel to the c-axis + + - title: Other Features + content: | + - **Two-phase fluid inclusions**: Liquid + gas + - **Colour zoning**: Irregular; some stones show a blue-grey core + - **Blue-grey core**: Relatively common in Montepuez material; can assist + identification alongside the inclusion suite + + - title: Apatite and Amphibole as Diagnostics + callout: + type: tip + title: Key Montepuez Inclusions + text: | + The combination of APATITE crystals (hexagonal prisms) and AMPHIBOLE needles + (greenish-black, elongated) in a ruby is strongly associated with the Montepuez + metamorphic assemblage. This pairing reflects the amphibolite host rock — + unlike the calcite + silk of Mogok, or the zircon + ilmenite of Thai basaltic ruby. + + - title: LA-ICP-MS Origin Determination + content: | + Analytical approach for Mozambique ruby: + subsections: + - title: Trace Element Suite + content: | + - **Principal elements**: V, Cr, Fe, Ga, Ti + - **Bivariate plots**: Fe/Ti vs Cr/Ga (separates basalt-type from marble-type); + V vs (Cr+V) (separates low-V Mogok from higher-V Mozambique) + - **Sr and Pb isotopes**: Krebs et al. (2020) demonstrated that isotope + ratios "significantly improved the discrimination" between geologically + similar settings + + - title: Mogok Overlap Challenge + content: | + - Type A Mozambique rubies can share low-Fe, high-Cr chemistry with Mogok; + multi-parameter analysis is mandatory for reliable origin determination + - No single test separates Mozambique from Mogok; the laboratory applies + a combination of chemical, spectroscopic, inclusion, and fluorescence data + + - title: Mavuco Paraíba-Type Tourmaline + content: | + The world's major African Paraíba-type source: + subsections: + - title: Deposit + content: | + - **Mavuco** deposit, Nampula Province, northern Mozambique — distinct from + the Montepuez ruby district (different province) + - Cu-bearing elbaite (Na(Li,Al)₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₄) producing the + characteristic neon blue-green Paraíba colour + + - title: Mn/Cu Origin Discrimination + content: | + - Abduriyim et al. (2006) demonstrated LA-ICP-MS fingerprinting of Cu-bearing + tourmaline from Brazil, Nigeria, and Mozambique; the key discriminator is + the **Mn/Cu ratio**: + - Brazil (Paraíba state): High Cu, relatively low Mn + - Nigeria: Intermediate; overlaps with Mozambique + - Mozambique: Generally higher Mn relative to Cu; Mn/Cu > ~0.3 tends to + indicate African provenance (Nigeria or Mozambique) + - Katsurada et al. (2019): "A combination of chemical, spectroscopic, and + gemological characteristics" required — Cu alone is insufficient + + - title: Properties + content: | + - **Colour**: Neon blue to blue-green to green; extraordinarily intense + due to Cu²⁺ and Mn³⁺ colouration + - **Cu²⁺**: Produces intense blue-green absorption band near 700 nm + - **RI**: 1.614–1.679 (uniaxial negative); birefringence ~0.016 + - **SG**: 3.01–3.06; Hardness: 7–7.5 + - Market premium: Brazilian Paraíba still commands higher premiums than + Mozambican/Nigerian by 100–300% — origin certification is commercially + critical + + - title: Market Position + content: | + Mozambique in the global gem trade: + + - Largest ruby producer by volume globally since ~2012; Gemfields's sealed-bid + auction system has created price transparency for commercial ruby + - Fine Type A Mozambique ruby (pigeon-blood quality from low-Fe primary material) + can achieve significant premiums but does not match Mogok premiums in the market + - Paraíba-type tourmaline from Mavuco commands substantial premiums over other + tourmaline origins but less than Brazilian Paraíba + +sources: + - doi: "10.5741/gems.51.1.44" + citation: "Chapin, Pardieu & Lucas (2015) Mozambique ruby. Gems & Gemology." + - doi: "10.5741/gems.55.2.162" + citation: "Vertriest & Saeseaw (2019) Comprehensive review of Mozambique ruby. Gems & Gemology." + - doi: "10.5741/gems.55.4.580" + citation: "Palke et al. (2019) Geographic Origin Determination of Ruby. Gems & Gemology." + - doi: "10.3390/min10050447" + citation: "Krebs et al. (2020) Expanded trace element suite + Sr-Pb isotopes for ruby origin. Minerals." + - doi: "10.5741/gems.42.1.4" + citation: "Abduriyim et al. (2006) Paraíba tourmaline Mn/Cu origin fingerprinting. Gems & Gemology." + - doi: "10.5741/gems.55.4.648" + citation: "Katsurada et al. (2019) Geographic origin determination of Paraíba-type tourmaline. Gems & Gemology." diff --git a/docs/learn/origin/pakistan/emerald.yaml b/docs/learn/origin/pakistan/emerald.yaml new file mode 100644 index 0000000..04646ef --- /dev/null +++ b/docs/learn/origin/pakistan/emerald.yaml @@ -0,0 +1,133 @@ +title: Swat Valley Emerald — Pakistan +description: Ophiolite-hosted Cr-rich emerald from Mingora, Swat Valley; three-phase fluid inclusions, chromian muscovite, low Li chemistry, talc-carbonate paragenesis. +order: 2 +category: origin +subcategory: pakistan +difficulty: advanced +icon: gem +related: + - origin/pakistan/overview + - origin/afghanistan/emerald + - origin/colombia + - origin/zambia + - species/emerald +tags: + - pakistan + - swat + - mingora + - emerald + - ophiolite + - chromium + - origin/pakistan + +sections: + - title: Introduction + content: | + The Swat Valley (Mingora area) of Khyber Pakhtunkhwa Province hosts one of the + world's significant emerald deposits, distinguished by its unique geological setting: + chromium-rich hydrothermal fluids from ophiolitic ultramafic rocks produced emerald + in talc-carbonate fracture systems along the Indus suture zone. Swat material is + noted for small stones with high colour saturation. + + - title: Geological Setting + content: | + Swat Valley emerald genesis: + subsections: + - title: Host Rock — Ophiolite Belt + content: | + - Hosted in carbonatised ultramafic rocks (ophiolite belt) of the Indus suture + zone, in the Mingora area of Swat Valley + - The Indus suture zone represents the ancient tectonic collision boundary + between the Indian and Eurasian plates; ophiolitic peridotite and chromite + are the Cr source + - Emerald-forming hydrothermal fluids penetrated fracture systems in the + talc-carbonate host rock derived from serpentinised ultramafic protolith + + - title: Chromium Source + content: | + - Chromium is sourced from ophiolitic chromite through hydrothermal fluid + interaction with the peridotite/serpentinite country rock + - Arif and Moon (2007) documented chromian muscovite and tourmaline in + emerald-bearing quartz veins: the muscovite shows "high Mg/Fe ratios (4–9) + and variable Ni" — geochemical evidence linking Cr directly to the ophiolitic + ultramafic host + + - title: Properties and Appearance + content: | + Characteristic features of Swat emerald: + + - **Colour**: Medium to deep green; highly saturated + - **Size**: Typically small (<2 ct clean); "small stones with saturated color" + is the standard trade descriptor; reserves estimated at ~70 million carats but + mostly small crystal size + - **Chromophore**: Cr³⁺ dominant; Cr/V ratio distinguishes ophiolite-hosted (Cr + dominant) from other deposit types + - **Fluorescence**: Strong red LWUV fluorescence driven by high Cr³⁺ + - **Chelsea Colour Filter**: Strong red (Cr dominant) + + - title: Diagnostic Inclusions + content: | + Guo et al. (2020) documented the inclusions of Swat emerald: + subsections: + - title: Fluid Inclusions + content: | + - **Three-phase fluid inclusions**: Liquid + gas + solid phases — documented + for the first time in Swat emeralds by Guo et al. (2020); diagnostic for + the high-salinity, high-temperature ophiolitic hydrothermal system + + - title: Mineral Inclusions + content: | + - **Chromian muscovite (chrome mica)**: Tabular brownish-green platelets; + very diagnostic for the ophiolite-belt genesis; rare in emeralds from + other deposit types + - **Actinolite needles**: Green amphibole; consistent with ultramafic host + - **Biotite platelets**: Brown tabular mica + - **Talc**: From the talc-carbonate host rock; soft and platy + + - title: Trace Element Chemistry + content: | + Chemical fingerprinting for origin determination: + subsections: + - title: Shared Low-Li Signature + content: | + - **Li < 200 ppmw** (lithium content): Shared with Colombian and Afghan emerald; + distinguishes from high-Li Zambian, Zimbabwe, and Ethiopian material + - The low-Li signature reflects a sediment/ophiolite geological heritage + rather than granitic pegmatite host + + - title: Separation from Other Low-Li Origins + content: | + - **Cr/V ratio**: Swat is Cr-dominant (ophiolite-Cr source); Colombian Chivor + is more V-dominant; Panjshir (Afghanistan) also Cr-dominant but with higher + Fe and distinct fluid inclusions + - **Other elements**: Sc, Mn, Co, Ni, Zn, Ga provide additional discrimination + in multivariate trace element analysis + - **UV-Vis**: Afghan Panjshir has "pronounced iron-related bands" not typical + of Colombian; Swat has its own spectral profile + + - title: Deposit Type Classification + callout: + type: info + title: Talc-Carbonate (Ophiolite-Belt) Type + text: | + Swat Valley emerald belongs to the "talc-carbonate" or "ophiolite-hosted" deposit + type — distinct from: + + - SCHIST-BELT type (Zambia, Zimbabwe, Russia, Ethiopia): schist host at + granite-ultramafic contact + - BLACK-SHALE type (Colombia): hydrothermal in sedimentary host with no igneous + proximity + - PEGMATITIC type (Brazil Carnaíba, parts of Brazil): emerald in pegmatites + + The ophiolite-belt context makes Swat inclusion suite (chromian muscovite, actinolite, + three-phase inclusions) unique among the major emerald sources. + +sources: + - doi: "10.5741/gems.56.3.336" + citation: "Guo et al. (2020) Inclusion and Trace Element Characteristics of Emeralds from Swat Valley, Pakistan. Gems & Gemology." + - doi: "10.2343/geochemj.41.475" + citation: "Arif & Moon (2007) Nickel-rich chromian muscovite from the Indus suture ophiolite, NW Pakistan. Geochemical Journal." + - doi: "10.3390/min9090561" + citation: "Karampelas et al. (2019) Emeralds from the Most Important Occurrences: Chemical and Spectroscopic Data. Minerals." + - doi: "10.5741/gems.55.4.614" + citation: "Saeseaw et al. (2019) Geographic Origin Determination of Emerald. Gems & Gemology." diff --git a/docs/learn/origin/pakistan/overview.yaml b/docs/learn/origin/pakistan/overview.yaml new file mode 100644 index 0000000..9d33b5e --- /dev/null +++ b/docs/learn/origin/pakistan/overview.yaml @@ -0,0 +1,104 @@ +title: Pakistan — Gem Origins Overview +description: Himalayan collision zone gem deposits — Swat emerald, Hunza ruby, Katlang topaz, Skardu aquamarine; multiple geological settings. +order: 1 +category: origin +subcategory: pakistan +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/pakistan/emerald + - origin/pakistan/ruby + - origin/pakistan/topaz + - origin/afghanistan/overview + - origin/kashmir +tags: + - pakistan + - swat + - hunza + - katlang + - skardu + - himalayan + - origin/pakistan + +sections: + - title: Introduction + content: | + Pakistan occupies a key position in the Himalayan collision zone, where the + convergence of the Indian and Eurasian plates has produced a diversity of gem + deposits unparalleled in a comparable geographic area. Three distinct geological + settings host different gem types: marble-hosted corundum in Hunza/Gilgit-Baltistan, + talc-carbonate ophiolite-hosted emerald in the Swat Valley, and calcite-vein pink + topaz at Katlang. Pegmatitic aquamarine and tourmaline from the Skardu region + complete Pakistan's gem portfolio. + + - title: Geological Settings + table: + headers: + - Region + - Setting + - Principal Gems + rows: + - ["Hunza / Gilgit-Baltistan", "Marble-hosted corundum (Himalayan suture)", "Ruby, pink sapphire"] + - ["Swat Valley (Mingora)", "Talc-carbonate / ophiolite belt (Indus suture)", "Emerald"] + - ["Katlang, Mardan", "Calcite veins in recrystallised limestone", "Pink topaz"] + - ["Skardu / Shigar, Baltistan", "LCT granitic pegmatites (Karakoram)", "Aquamarine, tourmaline, kunzite"] + + - title: Swat Valley Emerald — Brief Overview + content: | + - Hosted in carbonatised ultramafic rocks of the Indus suture zone; Cr sourced + from ophiolitic chromite + - Chromian muscovite and three-phase fluid inclusions are diagnostic + - Low Li (<200 ppmw) shared with Colombian and Afghan emerald + - See dedicated file: origin/pakistan/emerald + + - title: Hunza Ruby — Brief Overview + content: | + - Marble-hosted; low-Fe, high-Cr chemistry analogous to Mogok + - Strong red LWUV fluorescence; calcite and carbonate inclusions + - Small-scale artisanal production; laboratory separation from Mogok requires + LA-ICP-MS trace element fingerprinting + - See dedicated file: origin/pakistan/ruby + + - title: Katlang Pink Topaz — Brief Overview + content: | + - Colour caused by trace Cr³⁺ — rare in topaz globally + - Chromium colouring is the key diagnostic distinguishing from irradiation-induced + pink topaz or Mn-coloured topaz + - See dedicated file: origin/pakistan/topaz + + - title: Skardu Aquamarine and Tourmaline + content: | + Pakistan is one of the world's finest aquamarine sources: + + - **Host**: Granite pegmatites intruding high-grade metamorphic and granitic rocks + of the Karakoram; Baltistan and Gilgit-Baltistan produce world-class aquamarine, + rubellite, green tourmaline, and kunzite + - **Quality**: Skardu-region aquamarine is among the finest globally — typically + deeply coloured, large crystals with good clarity + - **Origin determination**: No distinctive chemical fingerprint for trade-level + origin determination beyond provenance documentation; properties are within the + normal species range + + - title: Conflict and Mining + callout: + type: warning + title: Security and Access + text: | + Security conditions in Khyber Pakhtunkhwa (Swat Valley, Katlang area) have + periodically disrupted mining operations. The Swat region experienced significant + insurgency in 2007–2009; access for international buyers has been variable. + Hunza Valley (Gilgit-Baltistan) is generally more accessible but remains remote. + + Ethical sourcing and chain-of-custody documentation are recommended for high-value + Pakistani gems, particularly Swat emeralds. + +sources: + - doi: "10.5741/gems.56.3.336" + citation: "Guo et al. (2020) Inclusion and Trace Element Characteristics of Emeralds from Swat Valley, Pakistan. Gems & Gemology." + - doi: "10.2343/geochemj.41.475" + citation: "Arif & Moon (2007) Nickel-rich chromian muscovite from the Indus suture ophiolite, NW Pakistan. Geochemical Journal." + - doi: "10.5741/gems.22.3.140" + citation: "Gübelin, Graziani & Kazmi (1986) Pink Topaz from Pakistan. Gems & Gemology." + - doi: "10.5741/gems.46.3.188" + citation: "Shigley et al. (2010) Gem Localities of the 2000s. Gems & Gemology." diff --git a/docs/learn/origin/pakistan/ruby.yaml b/docs/learn/origin/pakistan/ruby.yaml new file mode 100644 index 0000000..b15f873 --- /dev/null +++ b/docs/learn/origin/pakistan/ruby.yaml @@ -0,0 +1,101 @@ +title: Hunza Ruby — Pakistan +description: Marble-hosted ruby from Hunza/Gilgit-Baltistan; low-Fe high-Cr chemistry analogous to Mogok; marble-suite inclusions; strong LWUV fluorescence. +order: 3 +category: origin +subcategory: pakistan +difficulty: advanced +icon: gem +related: + - origin/pakistan/overview + - origin/burma/ruby + - origin/vietnam + - origin/afghanistan/ruby + - species/corundum +tags: + - pakistan + - hunza + - gilgit-baltistan + - ruby + - marble-hosted + - corundum + - origin/pakistan + +sections: + - title: Introduction + content: | + Ruby from the Hunza Valley (Gilgit-Baltistan) is marble-hosted corundum formed in + the Himalayan suture zone — the same broad orogenic setting that produced Mogok + (Burma), Luc Yen (Vietnam), and Kuh-i-Lal (Tajikistan) gems. Hunza ruby shares + the low-iron, high-chromium chemistry of marble-hosted corundum globally and can + approach Mogok quality in fine material, though production scale is small and + artisanal. + + - title: Geological Setting + content: | + Hunza ruby formation: + + - **Host rock**: Corundum-bearing marble; Okrusch, Bunch, and Bank (1976) established + the petrogenesis of the Hunza marble corundum — a "corundum-bearing marble" in + the Himalayan collision zone + - **Tectonic context**: Himalayan suture zone analogous to Mogok; carbonate platform + rocks metamorphosed during continental collision produced marble-hosted corundum + under low-Fe conditions + - **Location**: Gilgit-Baltistan; artisanal mining in remote high-altitude valleys + + - title: Properties + content: | + Marble-hosted chemical signature: + subsections: + - title: Colour + content: | + - Pinkish-red to red; fine quality material is comparable in colour to Mogok + - Absence of iron darkening (low-Fe marble chemistry) allows Cr to dominate + the optical response — vivid, pure red + - Some material has pink modifiers; range includes pink corundum/sapphire + transitional material + + - title: Fluorescence + content: | + - **Strong red LWUV fluorescence**: High Cr, low Fe — same principle as Mogok + - This is a primary distinguishing feature from Thai/Cambodian basaltic ruby + where iron quenches fluorescence + + - title: Inclusions + content: | + - Calcite and carbonate minerals (marble-hosted suite) + - Primary fluid inclusions: CO₂-rich with multi-solid residues — as confirmed + in Asian marble ruby deposits by Giuliani et al. (2015); brine compositions + differ between Asian marble ruby localities + - Low-Fe mineral assemblage consistent with marble protolith + + - title: Distinction from Mogok + content: | + Laboratory separation of Hunza from Mogok ruby: + + - Both share: low Fe (<300 ppm), strong red fluorescence, marble-suite inclusions + - **LA-ICP-MS required**: Trace element ratios (Ga/Mg and other patterns) can + separate Hunza from Mogok — this is a laboratory-level criterion + - **Oxygen isotopes**: Values differ subtly between marble ruby localities; + isotope analysis adds discrimination power + - **Specific fluid inclusion salt chemistry**: Differs between Asian marble ruby + deposits; brine composition from fluid inclusion microthermometry assists + + - title: Market Notes + callout: + type: info + title: Small-Scale Production + text: | + Hunza ruby production is artisanal and small-scale; the material rarely appears + in large volumes on the international market. Fine quality Hunza ruby commands + origin interest but does not achieve Mogok premiums on the current market. + + Security and access in Gilgit-Baltistan have improved in recent years; production + continuity has been variable historically. + +sources: + - doi: "10.1007/bf00203079" + citation: "Okrusch, Bunch & Bank (1976) Paragenesis of corundum-bearing marble at Hunza. Mineralium Deposita." + - doi: "10.1127/ejm/2015/0027-2442" + citation: "Giuliani et al. (2015) Fluid inclusions in ruby from Asian marble deposits. European Journal of Mineralogy." + - doi: "10.5741/gems.55.4.536" + citation: "Palke et al. (2019) Geographic Origin Determination of Blue Sapphire. Gems & Gemology." diff --git a/docs/learn/origin/pakistan/topaz.yaml b/docs/learn/origin/pakistan/topaz.yaml new file mode 100644 index 0000000..d81f400 --- /dev/null +++ b/docs/learn/origin/pakistan/topaz.yaml @@ -0,0 +1,105 @@ +title: Katlang Pink Topaz — Pakistan +description: Chromium-coloured pink to champagne topaz from Katlang, Mardan district; Cr³⁺ colouring diagnostic, calcite-vein hosted, rare among topaz globally. +order: 4 +category: origin +subcategory: pakistan +difficulty: advanced +icon: gem +related: + - origin/pakistan/overview + - species/topaz +tags: + - pakistan + - katlang + - topaz + - pink-topaz + - chromium + - origin/pakistan + +sections: + - title: Introduction + content: | + Pink topaz from the Katlang deposit in the Mardan district of Khyber Pakhtunkhwa + is exceptional among topaz varieties worldwide: its pink to pinkish-orange colour + is caused by trace chromium (Cr³⁺) — an extremely rare colouring mechanism for + topaz. Most pink topaz on the market is either irradiation-induced pink (colourless + topaz irradiated and heat-treated) or Mn-coloured. Katlang material is genuinely + Cr-coloured, making it diagnostically distinct and scientifically noteworthy. + + - title: Geological Setting + content: | + Katlang mine geology: + + - **Host**: Narrow calcite veins in recrystallised limestone (marble); the topaz + crystallises within vein cavities + - **Location**: Katlang, Mardan district, Khyber Pakhtunkhwa; the deposit was + documented by Spengler (1985) and Gübelin, Graziani and Kazmi (1986) + - **Crystal habit**: Well-formed prismatic crystals; sizes typically small (up to + 3 cm reported); associated colourless, reddish-brown, and tan topaz also recovered + - **Topaz species**: Al₂SiO₄(F,OH)₂; the F/OH ratio at Katlang influences specific + physical constants (RI, optic axial angle, unit cell dimensions) + + - title: Colour and Chromophore + content: | + What makes Katlang topaz unique: + subsections: + - title: Chromium Colouring + content: | + - **Confirmed chromophore**: Gübelin et al. (1986) confirmed "the color is due + to trace elements — principally chromium (Cr³⁺)" + - This Cr³⁺ substitution produces pink to pinkish-orange to champagne colour + through absorption in the yellow-green region (~550 nm) + + - title: Colour Range + content: | + - **Pink**: Most prized; pure pink with slight orange modifier + - **Pinkish-orange (peach)**: Transition colour between pink and champagne + - **Champagne**: Golden-yellow with slight pinkish cast + - Colourless, reddish-brown, and tan material is also recovered from the + same vein system but lacks the Cr colouring + + - title: Distinguishing Katlang from Other Pink Topaz + table: + headers: + - Property + - Katlang (Cr-coloured) + - Irradiated Pink Topaz + - Mn-Coloured Pink Topaz + rows: + - ["Chromophore", "Cr³⁺", "Colour centres (radiation)", "Mn³⁺"] + - ["Absorption spectrum", "Cr bands (~550 nm, ~670 nm)", "Different band pattern", "Mn band (~490 nm)"] + - ["Chelsea filter", "Reddish (Cr response)", "Inert or faint", "May show weak response"] + - ["Stability", "Stable", "May fade in light/heat", "Generally stable"] + - ["Origin", "Pakistan only (major source)", "Any country's colourless topaz", "Various sources"] + - ["Treatment", "Natural colour", "Treated", "Natural"] + + - title: Chromium in Topaz + callout: + type: info + title: A Rare Chromophore + text: | + Chromium colouring is extremely rare in topaz. Most natural pink topaz owes its + colour to colour centres created by natural irradiation, which are unstable and + may fade on exposure to light or heat. Katlang topaz is one of very few localities + in the world producing topaz coloured by actual Cr³⁺ substitution into the lattice. + + This makes Katlang material among the most scientifically interesting topaz types + and means it will not fade under normal wearing conditions — a practical advantage + over irradiation-treated pink topaz. + + - title: Physical Properties + content: | + Properties of Katlang topaz: + + - **Species formula**: Al₂SiO₄(F,OH)₂; orthorhombic; biaxial positive + - **RI**: 1.619–1.627 (α), 1.620–1.628 (β), 1.627–1.636 (γ); birefringence ~0.008–0.010 + - **SG**: ~3.49–3.57 + - **Hardness**: 8 (Mohs) + - **Note**: Gübelin et al. noted the F/OH ratio variation at Katlang affects + measured RI and optic axial angle compared to typical high-F topaz values + +sources: + - doi: "10.5741/gems.22.3.140" + citation: "Gübelin, Graziani & Kazmi (1986) Pink Topaz from Pakistan. Gems & Gemology." + - doi: "10.15506/jog.1985.19.8.664" + citation: "Spengler (1985) The Katlang Pink Topaz Mine, North West Frontier Province, Pakistan. Journal of Gemmology." diff --git a/docs/learn/origin/russia/alexandrite.yaml b/docs/learn/origin/russia/alexandrite.yaml new file mode 100644 index 0000000..c86ba60 --- /dev/null +++ b/docs/learn/origin/russia/alexandrite.yaml @@ -0,0 +1,144 @@ +title: Russian Alexandrite — Tokovaya District, Ural Mountains +description: Tokovaya district alexandrite — 1830 discovery, named for Tsar Alexander II; benchmark colour change; mica-schist host; market position vs synthetic. +order: 3 +category: origin +subcategory: russia +difficulty: advanced +icon: gem +related: + - origin/russia/overview + - origin/russia/emerald + - origin/ceylon + - species/chrysoberyl +tags: + - russia + - urals + - alexandrite + - chrysoberyl + - colour-change + - tokovaya + - sanarka + - origin/russia + +sections: + - title: Introduction + content: | + Russian alexandrite from the Tokovaya River district is the global benchmark for + chrysoberyl colour-change quality. Discovered in 1830 and named for the future + Tsar Alexander II, the stone exhibits the most valued colour-change in the gem world: + a distinctly blue-green to green in daylight shifting to raspberry-red to purple-red + under incandescent light. No other alexandrite source consistently matches this + quality of colour change. + + - title: Discovery and History + content: | + Tokovaya district history: + + - **1830**: Russian alexandrite discovered in mica schists of the Tokovaya River + district (Sanarka basin), approximately 80 km east of Yekaterinburg, Southern Urals + - Named in honour of Tsarevich Alexander (later Tsar Alexander II) — the discovery + reportedly occurred on the day of his coming of age + - The locality also hosts the Izumrudnye Kopi (Emerald Mines) district — the same + mica-schist geological setting produces both alexandrite and emerald + - Russian alexandrite was fashionable in late 19th century European jewellery; + stones remain among the most valuable chrysoberyl specimens + + - title: Geological Setting + content: | + Host rock and genesis: + + - **Host rock**: Mica schist (phlogopite-bearing) at the contact between + granitic pegmatites and Cr-enriched ultramafic country rocks + - **Genetic model**: Pegmatite supplies Be and Al; ultramafic country rock supplies Cr + - This Be + Al + Cr combination is the universal alexandrite-forming system, + also seen at Brazil (Minas Gerais), Sri Lanka, and India (Andhra Pradesh) + - Sanarka River basin = additional related locality + + - title: Properties + table: + headers: + - Property + - Value + rows: + - ["Composition", "BeAl₂O₄ (chrysoberyl), Cr³⁺ substituting Al³⁺"] + - ["Crystal system", "Orthorhombic; biaxial positive"] + - ["RI", "1.745–1.757 (α); birefringence 0.008–0.010"] + - ["SG", "3.73"] + - ["Hardness", "8.5 (Mohs)"] + - ["Pleochroism", "Trichroic — green / orange-yellow / red (strong)"] + - ["Chelsea Colour Filter", "Pinkish-red to red (Cr³⁺ response)"] + - ["Fluorescence", "Moderate red under LWUV; stronger under SWUV"] + - ["Key absorption", "680 nm Cr doublet; 645 nm; 580 nm band"] + + - title: Colour Change — The Russian Standard + content: | + What defines Russian alexandrite quality: + subsections: + - title: Daylight Colour + content: | + - Distinctly blue-green to green; often described as "emerald green" or + "peacock blue" in fine stones + - The saturation and clarity of the green is the first criterion of quality + + - title: Incandescent Colour + content: | + - Raspberry red to purple-red; vivid and saturated in fine material + - The change should be complete — not a muddy intermediate + - "The Russian standard": the most balanced and distinct colour change + of any alexandrite source + + - title: Mechanism + content: | + - Cr³⁺ in BeAl₂O₄ creates two transmission windows: ~550 nm (green) and + ~680 nm (red) + - Under daylight (blue-rich illuminant), the eye perceives green + - Under incandescent light (red-rich), the eye perceives red + - The sharpness of the change depends on how cleanly Cr³⁺ absorbs the + intermediate wavelengths (~580–640 nm) + + - title: Inclusions + content: | + Russian alexandrite inclusions: + + - **Phlogopite mica flakes**: From the mica-schist host; brownish tabular platelets + - **Two-phase fluid inclusions**: Liquid + gas + - **Fingerprints / healed fractures** + - **Elongated crystals** parallel to crystallographic axes + - Russian alexandrite is characteristically cleaner than Brazilian material; + clean stones >1 ct are extremely rare and correspondingly valuable + + - title: Distinguishing from Synthetic Alexandrite + callout: + type: warning + title: Natural vs Synthetic Alexandrite + text: | + Synthetic alexandrite (Czochralski and flux methods) has the identical Cr³⁺ + absorption spectrum and colour-change mechanism as natural. Distinction REQUIRES + microscopic inclusion examination: + + - **Czochralski synthetic**: Curved growth striae (parallel to growth front); + nail-head spicules characteristic of pulled-from-melt growth + - **Flux synthetic**: Twisted fingerprints; wispy veils; Pt platelets possible; + no curved striae + - **Natural Russian**: Phlogopite mica flakes; two-phase inclusions; no curved + striae; no Pt platelets + + UV fluorescence alone is NOT sufficient to separate natural from synthetic. + + - title: Market Position + content: | + Russian alexandrite in the market: + + - **Highest premiums**: Fine Russian Ural alexandrite with strong colour change + and good size commands the highest prices in the alexandrite market + - **Typical values**: Fine stones >1 ct: $10,000–50,000/ct depending on change + quality, colour saturation, clarity, and size + - **Unheated premium**: Natural colour — no treatment issue in alexandrite; + focus is on natural vs synthetic and origin origin + - **Alternative sources**: Brazil, Sri Lanka, India, and East Africa produce + alexandrite; none consistently match Ural quality; Brazilian material is the + primary commercial alternative for larger stones + +sources: + - doi: "10.5741/gems.30.4.243" + citation: "Kissin (1994) Ruby and Sapphire from the Southern Ural Mountains, Russia. Gems & Gemology." diff --git a/docs/learn/origin/russia/demantoid.yaml b/docs/learn/origin/russia/demantoid.yaml new file mode 100644 index 0000000..c5d54a8 --- /dev/null +++ b/docs/learn/origin/russia/demantoid.yaml @@ -0,0 +1,161 @@ +title: Russian Demantoid Garnet — Ural Mountains +description: Ural demantoid (andradite, Cr-coloured); horsetail inclusions — byssolite terminology and Kissin 2021 mineralogical correction; LA-ICP-MS origin discrimination from Namibia and Madagascar. +order: 2 +category: origin +subcategory: russia +difficulty: advanced +icon: gem +related: + - origin/russia/overview + - species/garnet +tags: + - russia + - urals + - demantoid + - andradite + - garnet + - horsetail + - byssolite + - chromite + - origin/russia + +sections: + - title: Introduction + content: | + Russian demantoid garnet from the Ural Mountains is the rarest and most prized + variety of andradite garnet and among the most valuable of all garnets. Discovered + in the 1860s from alluvial placers along the Bobrovka River (tributary of the Sysert), + it is coloured by Cr³⁺ and possesses the highest dispersion (0.057 B–G interval) + of any natural garnet — exceeding diamond (0.044). The name derives from German + "Demant" (diamond), referring to this exceptional fire. + + - title: Discovery and History + content: | + Ural demantoid history: + + - The name "demantoid" was proposed in 1856 by Finnish mineralogist Nils von + Nordensheld referring to diamond-like fire; confirmed as andradite garnet in 1874 + - Commercial gem-quality crystals were recovered from alluvial gravels of the + **Bobrovka River** (Sysert area, Sverdlovsk Oblast) beginning in the 1860s + - Additional primary occurrences at Poldniovaya, Karkodino, and Nizhny Tagil district + - Late 19th century Russian demantoid became fashionable in European jewellery + (Fabergé pieces); stones command significant market premiums over Namibian + or Malagasy material + + - title: Properties + table: + headers: + - Property + - Value + rows: + - ["Species", "Andradite garnet — Ca₃Fe₂(SiO₄)₃; Cr³⁺ substituting Fe³⁺"] + - ["Crystal system", "Cubic (isometric); singly refractive"] + - ["RI", "1.880–1.895"] + - ["Dispersion (B–G)", "0.057 — highest of all natural garnets"] + - ["SG", "~3.84"] + - ["Hardness", "6.5 (Mohs)"] + - ["Colour", "Yellow-green to emerald-green (Cr³⁺ dominant)"] + - ["Key absorption", "685 nm Cr line; 440 nm blue-violet cutoff (iron)"] + - ["Fluorescence", "Inert (iron quenches)"] + + - title: The Horsetail Inclusion — Dual Terminology + content: | + The horsetail is the most diagnostic inclusion for Ural demantoid: + subsections: + - title: FGA Traditional Description (Byssolite / Asbestiform) + content: | + - **FGA examination terminology**: The "horsetail" inclusion consists of curved, + fan-shaped bundles of fine asbestiform fibres radiating from a central chromite + crystal — described in the gemmological tradition as "byssolite" (asbestiform + actinolite/amphibole variety) + - This is the terminology used by major gemological laboratories in origin + reports and is the description that FGA Diploma candidates must recognise + - Source: Phillips & Hyrsl (1996), "Russian Demantoid, Czar of the Garnet + Family," Gems & Gemology — API-confirmed [VERIFIED] + + - title: Mineralogical Correction (Kissin 2021) + content: | + - Kissin, Murzin, and Karaseva (2021) performed SEM, Raman, XRD, and thermal + analysis on the inclusion structure and found: "in most cases, 'horsetail' + inclusions in the Ural demantoid were represented by hollow channels and only + the outcrops, on the demantoid surface, were occasionally filled with serpentine" + - The fibres are primarily HOLLOW GROWTH CHANNELS; serpentine-phase fill occurs + only at crystal surface outcrops — not byssolite or chrysotile sensu stricto + throughout the inclusion body + - Source: Kissin et al. (2021), Minerals, doi: 10.3390/min11080825 — API-confirmed [VERIFIED] + + - title: Horsetail Terminology — Important Clarification + callout: + type: warning + title: Use Both Terms — Do Not Substitute Silently + text: | + VERIFIED.md Cross-File Conflict 1 requires that BOTH descriptions be presented: + + FOR FGA EXAMINATIONS AND LABORATORY REPORTS: The standard description is + "asbestiform fibres / byssolite radiating from a central chromite crystal" + — this reflects how major laboratories describe the inclusion and what + candidates must identify on exam papers. + + FOR SCIENTIFIC ACCURACY: Kissin et al. (2021) demonstrated the fibres are + primarily hollow growth channels with serpentine fill only at surface outcrops; + "byssolite" is not the correct mineralogical identity of the bulk inclusion + material. + + Both perspectives coexist in the literature; do not present one as if the other + does not exist. Citation: 10.3390/min11080825 (Kissin 2021). + + - title: Diopside Needles (Secondary Inclusion) + content: | + A secondary inclusion type also confirms Ural origin: + + - **Diopside needles**: Krzemnicki (1999) confirmed by Raman microspectroscopy + that "diopside needles" are present as inclusions in Russian demantoid — distinct + from the fibre horsetail; elongated, colourless to pale green + - Combined with the horsetail, diopside needles reinforce Ural provenance + - Source: doi: 10.5741/gems.35.4.192 [VERIFIED] + + - title: Origin Discrimination by LA-ICP-MS + table: + headers: + - Feature + - Ural (Russia) + - Namibia (Erongo) + - Madagascar + rows: + - ["Horsetail inclusions", "Present (chromite core)", "Absent", "Absent"] + - ["Diopside needles", "Occasional", "Absent", "Absent"] + - ["Host rock", "Serpentinite", "Skarn", "Skarn"] + - ["Mn/Ti ratio", "Low", "Intermediate", "Higher"] + - ["Wollastonite, fluorapatite", "Absent", "Present", "Present"] + - ["Diopside grains", "Needles (elongated)", "Absent", "Rounded groups present"] + + - title: Chemical Discrimination Note + content: | + Schwarzinger (2019) demonstrated that three major demantoid sources (Russia, Namibia, + Madagascar) can be distinguished by LA-ICP-MS: "the three major sources could be + distinguished by using a plot of the manganese/titanium ratio versus the sum of + chromium and vanadium in combination with the aluminum content." This chemical + separation supplements the inclusion-based diagnosis. + + - title: Market Position + content: | + Ural demantoid in the gem market: + + - Commands significant premium over Namibian and Malagasy material — attributable + primarily to the horsetail inclusion and historical prestige + - Fine Russian demantoid with prominent horsetail, good green colour, and >1 ct + weight is among the most collectible of all garnet varieties + - Supply is limited; alluvial placers are largely worked out; primary occurrences + yield small quantities + - Namibian demantoid (skarn-hosted, Erongo) is the principal commercial alternative + for clean, larger stones + +sources: + - doi: "10.5741/gems.32.2.100" + citation: "Phillips & Hyrsl (1996) Russian Demantoid, Czar of the Garnet Family. Gems & Gemology. [VERIFIED — live Crossref]" + - doi: "10.3390/min11080825" + citation: "Kissin, Murzin & Karaseva (2021) 'Horsetail' Inclusions in the Ural Demantoids: Growth Formations. Minerals. [VERIFIED — live Crossref]" + - doi: "10.5741/gems.35.4.192" + citation: "Krzemnicki (1999) Diopside needles as inclusions in demantoid garnet from Russia. Gems & Gemology. [VERIFIED]" + - doi: "10.1007/s00706-019-02409-3" + citation: "Schwarzinger (2019) LA-ICP-MS chemical fingerprinting of demantoid sources. Monatshefte für Chemie. [VERIFIED]" diff --git a/docs/learn/origin/russia/emerald.yaml b/docs/learn/origin/russia/emerald.yaml new file mode 100644 index 0000000..2b35bbd --- /dev/null +++ b/docs/learn/origin/russia/emerald.yaml @@ -0,0 +1,128 @@ +title: Ural Emerald — Malyshevsky, Russia +description: Ural emerald from the Malyshevsky/Izumrudnye Kopi deposit; phlogopite mica inclusions diagnostic; Cr+V chromophores; mica-schist contact zone genesis. +order: 4 +category: origin +subcategory: russia +difficulty: advanced +icon: gem +related: + - origin/russia/overview + - origin/russia/alexandrite + - origin/zambia + - origin/colombia + - species/emerald +tags: + - russia + - urals + - emerald + - malyshevsky + - izumrudnye-kopi + - phlogopite + - mica + - origin/russia + +sections: + - title: Introduction + content: | + Ural emerald from the Malyshevsky deposit (also Izumrudnye Kopi — "Emerald Mines") + has been mined since discovery in 1831. Located approximately 90 km northeast of + Yekaterinburg in Sverdlovsk Oblast, this is the same contact zone that produces + Russian alexandrite. The deposit occupies the contact between granitic pegmatites + and Cr-enriched mica schists. Russian emeralds are identified primarily by their + characteristic phlogopite mica inclusions. + + - title: Geological Setting + content: | + Ural emerald genesis: + + - **Host rock**: Phlogopite mica schist at the contact with granitic intrusions; + Laskovenkov and Zhernakov (1995) confirmed that the deposits consist of + "mica schists with phlogopite" along the Tokovaya River corridor + - **Genetic model**: Same as alexandrite — pegmatite supplies Be and Al; + Cr-enriched ultramafic/schist country rock supplies Cr; the intersection + of these sources at the contact zone enables beryl + Cr emerald formation + - **Deposit scale**: Malysheva mine is the largest known emerald deposit in Russia; + operated intermittently in the post-Soviet period + + - title: Properties + table: + headers: + - Property + - Value + rows: + - ["Formula", "Be₃Al₂Si₆O₁₈ (beryl), Cr³⁺ + V³⁺ colouring"] + - ["Crystal system", "Hexagonal; uniaxial negative"] + - ["RI", "1.577–1.583 (ω); 1.584–1.590 (ε); DR ~0.006–0.009"] + - ["SG", "2.72–2.77"] + - ["Hardness", "7.5–8 (Mohs)"] + - ["Chromophores", "Cr³⁺ (primary) + V³⁺ (secondary)"] + - ["Fluorescence (LWUV)", "Moderate red to orange-red; stronger than Colombian"] + - ["Chelsea Colour Filter", "Red (Cr³⁺ dominant)"] + - ["Key absorption", "680 nm Cr doublet (strong); 637 nm; 477 nm; 430 nm cutoff"] + + - title: Diagnostic Inclusions + content: | + Russian Ural emerald inclusion suite: + subsections: + - title: Primary Diagnostic — Phlogopite Mica + content: | + - **Phlogopite mica flakes**: Brownish, tabular platelets parallel to the + cleavage planes; the most characteristic and diagnostic inclusion for Ural + emerald origin + - These mica platelets derive directly from the phlogopite mica schist host rock + - Their brownish tabular habit distinguishes them from the calcite and pyrite + of Colombian emerald and from the tremolite needles of Sandawana (Zimbabwe) + + - title: Additional Inclusions + content: | + - **Tremolite needles**: Calcium-magnesium amphibole; slender, colourless + - **Two-phase fluid inclusions**: Liquid + gas + - **Actinolite** + - **Apatite**: Rounded crystals + - **Pyrite**: Present but less abundant than in Colombian material + + - title: Chromophore Profile + content: | + Cr³⁺ + V³⁺ in Ural emerald: + + - Both Cr and V are present as colouring agents; this dual chromophore profile + gives a colour profile slightly different from purely V-dominated Brazilian + (Itabira/Carnaíba) material and from the high-Cr Sandawana + - Compared to Colombian: less fluorescence (more Fe present); different colour + profile (Ural green tends toward warmer medium green rather than Colombian's + vivid pure green) + - Compared to Zambian: similar Cr+V but different inclusion suite (Zambia has + biotite, not phlogopite; distinct talc and chlorite inclusions) + + - title: Origin Discrimination + table: + headers: + - Feature + - Ural (Russia) + - Colombian (Muzo) + - Sandawana (Zimbabwe) + - Zambia + rows: + - ["Primary inclusion", "Phlogopite mica platelets", "Parisite + halite in 3-phase", "Tremolite needles", "Biotite mica platelets"] + - ["Pyrite", "Present (minor)", "Absent in Muzo; abundant in Chivor", "Absent", "Present"] + - ["Chromophore", "Cr + V", "Cr dominant", "Cr dominant (very high)", "Cr + V"] + - ["Fe content", "Low", "Very low", "Very low", "Moderate"] + - ["Fluorescence (LWUV)", "Moderate red–orange", "Strong red", "Very strong red", "Moderate red"] + - ["Li content", ">200 ppmw (higher)", "<200 ppmw", ">200 ppmw", ">200 ppmw"] + + - title: Market Notes + content: | + Ural emerald market position: + + - Below Colombian in prestige and price; quality is variable; fine material is + attractive but Ural production does not achieve the colour saturation of top + Colombian or Sandawana + - Malysheva deposit operates intermittently; supply is not continuous + - Russian emerald is prized by collectors for its historical interest and + characteristic mica inclusions + +sources: + - doi: "10.5741/gems.31.2.106" + citation: "Laskovenkov & Zhernakov (1995) The Ural Emerald Mines. Gems & Gemology." + - doi: "10.3390/min9090561" + citation: "Karampelas et al. (2019) Emeralds from the Most Important Occurrences. Minerals." diff --git a/docs/learn/origin/russia/overview.yaml b/docs/learn/origin/russia/overview.yaml new file mode 100644 index 0000000..810b6b3 --- /dev/null +++ b/docs/learn/origin/russia/overview.yaml @@ -0,0 +1,106 @@ +title: Russia — Ural Gem Deposits Overview +description: Ural Mountains gem belt — demantoid garnet, alexandrite, emerald; Yakutia diamond; serpentinite and mica-schist geological settings. +order: 1 +category: origin +subcategory: russia +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/russia/demantoid + - origin/russia/alexandrite + - origin/russia/emerald + - species/garnet + - species/chrysoberyl +tags: + - russia + - urals + - demantoid + - alexandrite + - emerald + - yakutia + - origin/russia + +sections: + - title: Introduction + content: | + The Ural Mountains of Russia host one of the world's most remarkable concentrations + of rare and collectible gem varieties: demantoid garnet (the finest andradite), the + benchmark alexandrite (the standard of colour-change quality), and Ural emerald from + the Malyshevsky deposit. The Ural belt stretches ~2,500 km and formed during + Late Palaeozoic (350–290 Ma) suturing of the Russian and Siberian plates. + + Russia also hosts the world's largest diamond production by volume in Yakutia + (Sakha Republic, eastern Siberia) — geographically and geologically distinct + from the Ural gem belt. + + - title: Geological Settings + table: + headers: + - Setting + - Location + - Gems Produced + rows: + - ["Serpentinised ultramafic bodies", "Central/south-central Urals", "Demantoid garnet, chrysotile serpentine"] + - ["Mica-schist / phlogopite contact zones", "Tokovaya River district", "Alexandrite, emerald"] + - ["Kimberlite pipes", "Yakutia / Sakha Republic (eastern Siberia)", "Diamond (Russian diamond)"] + + - title: Demantoid Garnet — Brief Overview + content: | + - Discovered 1860s; Bobrovka River and Sysert area, Sverdlovsk Oblast + - Andradite garnet (Ca₃Fe₂(SiO₄)₃), Cr³⁺-coloured; highest dispersion of + any natural garnet (0.057 — exceeds diamond 0.044) + - "Horsetail" inclusion is the single most diagnostic Ural feature + - See dedicated file: origin/russia/demantoid + + - title: Alexandrite — Brief Overview + content: | + - Discovered 1830; Tokovaya River district, ~80 km east of Yekaterinburg + - Named for Tsarevich Alexander (later Tsar Alexander II) + - Russian alexandrite = global benchmark for colour-change quality + - See dedicated file: origin/russia/alexandrite + + - title: Ural Emerald — Brief Overview + content: | + - Izumrudnye Kopi (Emerald Mines) + Malyshevsky deposit; ~90 km NE of Yekaterinburg + - Phlogopite mica inclusions are most diagnostic feature for Ural provenance + - Cr³⁺ + V³⁺ chromophores; mica-schist host at granite contact + - See dedicated file: origin/russia/emerald + + - title: Russian Diamond (Yakutia) + content: | + Russia is the world's largest diamond producer by volume (Alrosa company operations): + + - **Mir pipe** (Mirny): Discovered 1955; one of the largest kimberlite pipes; + underground mining continues + - **Udachnaya, Aikhal, Jubilee pipes** (Nyurba field): Major modern producers + - Russian Yakutian diamonds show the standard kimberlitic inclusion suite + (olivine/forsterite, pyrope garnet, chrome diopside, graphite) — no unique + macro-diagnostic features that distinguish them from other kimberlitic origins + at the gemmological bench level + - Separation from HPHT or CVD synthetic diamond uses standard spectroscopic + methods; origin determination of individual natural diamonds is not routinely + possible + + - title: Russia Diamond Diagnostics Note + callout: + type: warning + title: Russian Diamond Gemmological Diagnostics Unverified + text: | + No peer-reviewed gemmological paper specifically characterising Yakutian + kimberlitic diamond diagnostics was retrieved from the research database. + Russian diamonds are commercially significant but there are no specific + bench-level indicators that distinguish them from, for example, Botswanan or + Canadian kimberlitic diamonds. + + Standard diamond testing methods (fluorescence, spectroscopy, DiamondView, + DiamondSure) apply universally. Do not claim Russian-specific diamond + gemmological diagnostics without sourced literature. + +sources: + - doi: "10.5741/gems.30.4.243" + citation: "Kissin (1994) Ruby and Sapphire from the Southern Ural Mountains. Gems & Gemology." + - doi: "10.5741/gems.35.4.192" + citation: "Krzemnicki (1999) Diopside needles as inclusions in demantoid garnet. Gems & Gemology." + - doi: "10.5741/gems.31.2.106" + citation: "Laskovenkov & Zhernakov (1995) The Ural Emerald Mines. Gems & Gemology." diff --git a/docs/learn/origin/tajikistan.yaml b/docs/learn/origin/tajikistan.yaml new file mode 100644 index 0000000..72796e6 --- /dev/null +++ b/docs/learn/origin/tajikistan.yaml @@ -0,0 +1,141 @@ +title: Tajikistan — Kuh-i-Lal Spinel (Balas Ruby) +description: Kuh-i-Lal Gorno-Badakhshan red and pink spinel — historic "Balas ruby" of the Persian courts; Cr-coloured marble-hosted; trace element distinction from Mogok and Luc Yen. +order: 12 +category: origin +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/burma/spinel + - origin/vietnam + - origin/afghanistan/overview + - species/spinel +tags: + - tajikistan + - kuh-i-lal + - badakhshan + - spinel + - balas-ruby + - marble-hosted + - himalayan + - origin/tajikistan + +sections: + - title: Introduction + content: | + The Kuh-i-Lal deposit in the Gorno-Badakhshan Autonomous Region of Tajikistan is + the world's most historically celebrated red spinel locality. Known for centuries + as the source of "Balas ruby" — a Persian trade name for red spinel before spinel + was distinguished from ruby as a separate species — it supplied the gem courts of + the Islamic world, Persia, and Mughal India. The Black Prince's Ruby (set in the + Imperial State Crown of the United Kingdom) and the Timur Ruby are both Kuh-i-Lal + red spinels. The deposit lies in the same Himalayan orogenic belt as Mogok (Burma) + and Luc Yen (Vietnam). + + - title: Geological Context + content: | + Kuh-i-Lal sits at the junction of the Pamir Mountains and the Afghan border: + subsections: + - title: Himalayan Belt Affiliation + content: | + - Located in Badakhshan, geographically adjacent to Afghanistan's Sar-e-Sang + lapis mines — both deposits sit in the same Badakhshan province + - Part of the marble-hosted gem spinel belt extending from Mogok (Myanmar) + through Luc Yen (Vietnam) to Kuh-i-Lal; Malsy and Klemm (2010) stated + "Gem spinel deposits in Myanmar, Vietnam and Tajikistan have their formation + in association with Himalayan orogenesis" + - All are marble-hosted in regionally metamorphosed carbonate sequences + + - title: Mining + content: | + - High-altitude artisanal mining in marble outcrops of the Gorno-Badakhshan + Autonomous Region; accessibility is difficult + - Modern production is small-scale; material appears on the international market + but volumes are modest + - The "Kuhilal" mine name is also spelled Kuh-e-Lal or Kuh-i-Lal + + - title: Properties + content: | + Kuh-i-Lal spinel characteristics: + subsections: + - title: Colour + content: | + - Vivid red, orange-red, hot pink, mauve-pink; the historic "pigeon blood" + red spinel from this deposit set the standard for red spinel globally + - Colour caused by Cr³⁺ substituting Mg²⁺ in the spinel structure + - Liu et al. (2022) confirmed the Cr³⁺ colouring mechanism for Kuh-i-Lal + material through UV-Vis spectroscopy + + - title: Inclusion Suite + content: | + - Marble-hosted inclusions: calcite, apatite, dolomite, negative crystals + - Absence of titanite inclusions (which characterise Luc Yen) + - Absence of cobalt-blue colour variety (unique to Luc Yen) + - Octahedral negative crystals consistent with marble genesis + + - title: Fluorescence + content: | + - Strong red fluorescence under LWUV — Cr³⁺ dominant, relatively low Fe + - Similar in principle to Mogok ruby and Luc Yen spinel fluorescence + + - title: Trace Element Origin Determination + content: | + Separating Kuh-i-Lal from Mogok and Luc Yen spinels: + subsections: + - title: Key Chemical Differences + content: | + - Malsy and Klemm (2010) showed that trace element differences exist: "Ti, Fe, + Ni, Zn, Zr and Sn differ slightly in spinels from the sources investigated" + - Kuh-i-Lal spinels differ in **Ni, Zn, Sn** profiles from Luc Yen and Mogok + + - title: Diagnostic Table + items: + - name: Horsetail inclusions (demantoid reference) + description: N/A (not applicable to spinel) + - name: Titanite inclusions + description: Absent + - name: Co-blue colour variety + description: Absent + - name: "Ni, Zn, Sn profile" + description: Kuh-i-Lal characteristic pattern + - name: Host rock + description: Marble (calcite, apatite, negative crystals) + + - title: The Kuh-i-Lal Comparison Table + table: + headers: + - Feature + - Kuh-i-Lal (Tajikistan) + - Luc Yen (Vietnam) + - Mogok (Burma) + rows: + - ["Titanite inclusions", "Absent", "Present (diagnostic)", "Absent"] + - ["Cobalt-blue spinel", "Not produced", "Diagnostic feature", "Rare"] + - ["Marble inclusions", "Calcite, apatite, neg crystals", "Calcite, marble suite", "Apatite, calcite, neg crystals"] + - ["Ni/Zn/Sn profile", "Kuh-i-Lal characteristic", "Different", "Different"] + - ["Mn/Ti vs Cr+V", "Distinctive range", "Different range", "Different range"] + - ["LWUV fluorescence", "Strong red (Cr)", "Strong red (Cr)", "Strong red (Cr)"] + + - title: Historic "Balas Ruby" Name + callout: + type: info + title: The Balas Ruby Mystery Resolved + text: | + Before the 18th century, red spinel and ruby were not distinguished as separate + gem species. The name "Balas ruby" (from Balascia, the medieval name for Badakhshan) + referred to red stones from the Kuh-i-Lal region — most of which are spinel. + + Famous "rubies" in royal collections worldwide were later identified as Kuh-i-Lal + spinel: + - **Black Prince's Ruby** (Imperial State Crown, UK): A 170-carat red spinel + - **Timur Ruby** (Royal Collection Trust, UK): An historic red spinel inscribed + with names of its Mughal owners + + This historical confusion was resolved in the 19th century when mineralogists + distinguished spinel from corundum by crystal system and composition. + +sources: + - doi: "10.2533/chimia.2010.741" + citation: "Malsy & Klemm (2010) Distinction of Gem Spinels from the Himalayan Mountain Belt. CHIMIA International Journal for Chemistry." + - doi: "10.5741/gems.58.3.338" + citation: "Liu et al. (2022) Color Mechanism and Spectroscopic Thermal Variation of Pink Spinel from Kuh-i-Lal, Tajikistan. Gems & Gemology." diff --git a/docs/learn/origin/thailand/overview.yaml b/docs/learn/origin/thailand/overview.yaml new file mode 100644 index 0000000..b43072c --- /dev/null +++ b/docs/learn/origin/thailand/overview.yaml @@ -0,0 +1,122 @@ +title: Thailand — Gem Origins Overview +description: Southeast Asian gem province centred on Chanthaburi, Trat, Kanchanaburi, Bo Phloi, and Bo Rai; world leader in corundum heat treatment and trading. +order: 1 +category: origin +subcategory: thailand +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/thailand/ruby + - origin/thailand/sapphire + - origin/thailand/zircon + - origin/cambodia + - origin/burma/ruby + - species/corundum +tags: + - thailand + - chanthaburi + - trat + - kanchanaburi + - basaltic + - origin/thailand + +sections: + - title: Introduction + content: | + Thailand hosts one of the most important gem-producing provinces in Southeast Asia, + centred on Cenozoic alkali basalt fields in the east (Chanthaburi-Trat) and west + (Kanchanaburi). Though primary ruby deposits are largely exhausted, Bangkok and + Chanthaburi remain the world's dominant centres for corundum heat treatment and + the international ruby and sapphire trade. + + - title: Geological Context + content: | + All Thai corundum deposits share a basaltic origin: + subsections: + - title: Basaltic Province + content: | + - **Setting**: Cenozoic intraplate alkali basalt fields along the Indochina block + - **Age**: Neogene to Quaternary volcanic activity + - **Transport**: Corundum crystallised at mantle depth and was transported to + the surface by alkali basalt magmas + - **Concentration**: Gems accumulate in alluvial and eluvial placers derived + from weathered basalt + - **Chemistry**: Basaltic environment imposes high-Fe, low-Cr signature on + corundum — the defining geochemical contrast with marble-hosted Mogok ruby + + - title: Tectonic Context + content: | + - Post-subduction intraplate extension of the Indochina microplate + - Multi-stage sapphire formation at Bo Phloi reflects separate pulses + of basaltic magmatism + - Same Southeast Asian alkaline basalt province as Cambodian Pailin field + — deposits merge across the border + + - title: Mining Areas + table: + headers: + - District + - Province + - Products + - Status + rows: + - ["Bo Rai", "Trat", "Ruby (historic 'Siam ruby')", "Largely exhausted"] + - ["Bo Welu / Khlung", "Chanthaburi", "Ruby, blue/yellow sapphire", "Limited activity"] + - ["Bo Phloi", "Kanchanaburi", "Blue and yellow sapphire", "Mostly closed, well-studied"] + - ["Kanchanaburi town area", "Kanchanaburi", "Blue sapphire", "Historic"] + + - title: Production History + content: | + Thailand's rise and evolution as a gem hub: + subsections: + - title: Rise to Prominence + content: | + - 1970s–1980s: Thailand became the world's dominant ruby source after Mogok + production declined; Keller (1982) noted Thailand had become "the world's + major source of gem ruby" following "the recent drastic decline in production + from the classic ruby mines of Burma" + - Bo Rai ruby production peaked in the 1970s–1980s; now essentially exhausted + + - title: Treatment and Trading Hub + content: | + - Bangkok and Chanthaburi developed into the world's dominant ruby and sapphire + heat-treatment and trading centres + - Thailand pioneered the technology of heating Thai and Burmese rough to dissolve + silk and improve colour + - Material from Thailand, Cambodia, Vietnam, Burma, and East Africa is routinely + treated and traded through Chanthaburi + + - title: Zircon Trade Hub + content: | + Beyond ruby and sapphire, Thailand is the global centre for blue zircon production: + + - Cambodian and Vietnamese zircon rough is imported to Chanthaburi and Bangkok + - Heat treatment in oxidising conditions at 900–1000°C converts brownish rough + to the prized "blue zircon" colour + - Thailand exports the majority of the world's faceted blue zircon + + - title: Basaltic vs Marble-Hosted Corundum + callout: + type: info + title: The Key Distinction + text: | + All Thai corundum is basaltic-hosted. This produces a fundamentally different + geochemical and gemmological profile from marble-hosted material (Burma, Kashmir, + Vietnam, Pakistan): + + - HIGH iron content (>600 ppm, often >1,000 ppm Fe) + - WEAK to INERT LWUV fluorescence (iron quenches chromium fluorescence) + - STRONG 450–470 nm iron absorption triplet in UV-Vis spectra + - BASALT-SUITE inclusions (zircon, ilmenite, alkali feldspar, enstatite) + - ABSENT: calcite, apatite, sphene typical of marble-hosted material + +sources: + - doi: "10.5741/gems.18.4.186" + citation: "Keller (1982) The Chanthaburi-Trat Gem Field, Thailand. Gems & Gemology." + - doi: "10.5741/gems.55.3.354" + citation: "Promwongnan & Sutthirat (2019) Mineral Inclusions in Ruby from Bo Welu, Chanthaburi. Gems & Gemology." + - doi: "10.1016/j.jseaes.2019.104068" + citation: "Sutthirat et al. (2019) Multistages of sapphire formation, Bo Phloi. Journal of Asian Earth Sciences." + - doi: "10.5741/gems.45.4.236" + citation: "Shor & Weldon (2009) Ruby and Sapphire Production and Distribution. Gems & Gemology." diff --git a/docs/learn/origin/thailand/ruby.yaml b/docs/learn/origin/thailand/ruby.yaml new file mode 100644 index 0000000..92d7ebf --- /dev/null +++ b/docs/learn/origin/thailand/ruby.yaml @@ -0,0 +1,157 @@ +title: Thai Ruby — Chanthaburi-Trat and Bo Rai Types +description: Basaltic-hosted Siam ruby from Chanthaburi-Trat and Bo Rai; diagnostic high-Fe chemistry, 451/460/470 nm iron triplet, weak fluorescence, alluvial habit. +order: 2 +category: origin +subcategory: thailand +difficulty: advanced +icon: gem +related: + - origin/thailand/overview + - origin/burma/ruby + - origin/cambodia + - origin/east-africa/ruby + - species/corundum +tags: + - thailand + - ruby + - chanthaburi + - trat + - bo-rai + - basaltic + - corundum + - siam-ruby + +sections: + - title: Introduction + content: | + Thai ruby from the Chanthaburi-Trat province and adjacent Bo Rai (Trat Province) + represents the classic "Siam ruby" of the gem trade. All Thai ruby is basalt-hosted: + gems crystallised at mantle depth and were transported to the surface in alkali + basalt magmas, concentrating in alluvial placers. The high-iron basaltic environment + distinguishes Thai ruby sharply from low-iron marble-hosted Mogok material. + + - title: Colour and Appearance + content: | + Characteristic appearance of Thai basaltic ruby: + subsections: + - title: Colour + content: | + - **Hue**: Red to slightly purplish-red; often darker than Mogok material + - **Brownish modifier**: Common due to high iron content; iron absorbs in the + blue-green region and shifts the colour toward brownish-red + - **Saturation**: High in fine material but rarely achieves the vivid "pigeon + blood" quality of Mogok ruby + - **Fluorescence response**: Colour appears dull or dead under UV — iron + strongly quenches chromium fluorescence + + - title: Transparency and Cut + content: | + - Typically water-worn, rounded alluvial pebbles — evidence of secondary deposit + - Variable clarity; extensive rutile silk common + - Most commercial material is heat-treated to improve colour and clarity + + - title: The Iron Absorption Triplet + callout: + type: info + title: Diagnostic UV-Vis Feature + text: | + The single most important spectroscopic diagnostic for Thai and Cambodian basaltic + ruby is the IRON ABSORPTION TRIPLET at approximately 451, 460, and 470 nm. + + These three closely spaced bands in the blue-violet region arise from Fe²⁺–Ti⁴⁺ + intervalence charge transfer and Fe–Fe interactions in the high-iron corundum lattice. + The triplet is VERY STRONG in basaltic ruby and produces the characteristic brownish + undertone by absorbing blue light. It is ABSENT or very weak in marble-hosted + (Mogok, Vietnam, Kashmir) material. + + - title: Diagnostic Inclusions + table: + headers: + - Inclusion + - Description + - Significance + rows: + - ["Zircon crystals", "Common; often with radiation damage tension halos", "Basaltic parentage marker"] + - ["Ilmenite", "Manganiferous; black opaque", "High-Fe basaltic environment"] + - ["Enstatite", "Silica-rich; pyroxene group", "Diagnostic for xenolith-origin basaltic ruby"] + - ["Alkali feldspar", "White to colourless inclusions", "Deep crustal/mantle xenolith suite"] + - ["Almandine-pyrope garnet", "Rounded crystals", "Xenolith association"] + - ["Sapphirine", "Blue-green; rare but diagnostic", "High-P basaltic xenolith environment"] + - ["Biotite-phlogopite mica", "Brown platelets", "Basaltic mantle xenolith"] + - ["Rutile silk", "Coarse, irregular networks", "Differs from fine Mogok silk"] + - ["Calcite / apatite / sphene", "ABSENT", "Presence would indicate marble-hosted origin"] + + - title: Inclusions Note + callout: + type: tip + title: What Is Absent Is As Diagnostic As What Is Present + text: | + The ABSENCE of marble-suite inclusions (calcite, apatite, sphene, pargasite) is + as diagnostic as the presence of basalt-suite minerals. If calcite rhombs are seen + in a red corundum, a marble-hosted origin (Mogok, Vietnam, Pakistan) must be considered. + + - title: Origin Determination Criteria + content: | + Laboratory criteria for confirming Thai basaltic ruby origin: + subsections: + - title: Chemical Criteria (LA-ICP-MS) + content: | + - **Fe content**: High (>600 ppm; often >1,000 ppm) — primary criterion + - **Fe/Cr ratio**: High relative to marble-hosted ruby + - **Ga/Mg**: Basaltic sapphire signature; specific ratio differs from marble-hosted + - **Low Cr relative to Fe**: Weak chromium signal suppressed by high iron + + - title: Optical / Spectroscopic Criteria + content: | + - Very strong 451/460/470 nm iron absorption triplet in UV-Vis + - LWUV fluorescence: Weak to inert (iron quenches chromium fluorescence) + — major contrast with marble-hosted ruby + - Chromium doublet at 692/694 nm present but may be accompanied by strong + broad iron absorption + - Chelsea filter: May appear weakly red (Cr present) but less vividly than + Mogok material + + - title: Inclusion Criteria + content: | + - Basalt-xenolith mineral suite: zircon, ilmenite, enstatite, feldspar, sapphirine + - ABSENCE of calcite, apatite, sphene, pargasite + - Coarse, irregular rutile networks rather than fine short Mogok-type silk + + - title: Comparison with Mogok Ruby + table: + headers: + - Feature + - Thai (Basaltic) + - Mogok (Marble-hosted) + rows: + - ["Fe content", "High (>600–1,000 ppm)", "Low (<300 ppm)"] + - ["LWUV fluorescence", "Weak to inert", "Strong red"] + - ["451/460/470 nm triplet", "Very strong", "Absent or very weak"] + - ["Colour modifier", "Often brownish-red", "Pure red / pigeon blood"] + - ["Key inclusions", "Zircon, ilmenite, enstatite", "Calcite, apatite, sphene, silk"] + - ["Silk character", "Coarse, irregular networks", "Fine, short rutile needles"] + - ["Geological host", "Cenozoic alkali basalt", "Precambrian marble"] + - ["Market premium", "Lower", "Highest"] + + - title: Market and Treatment + content: | + Thai ruby in the modern gem trade: + + - **Heat treatment**: Nearly universal for commercial material; dissolves silk, + improves colour; readily accepted and disclosed + - **Unheated Thai ruby**: Uncommon; little premium (basaltic character remains diagnostic) + - **Market position**: Below Mogok, Mozambique primary; valued for volume supply + - **Trade history**: Bo Rai deposits largely exhausted by 1990s; most "Thai ruby" + in trade today originates from Cambodia, Vietnam, or East Africa, heated in Thailand + +sources: + - doi: "10.5741/gems.55.3.354" + citation: "Promwongnan & Sutthirat (2019) Mineral Inclusions in Ruby from Bo Welu, Chanthaburi. Gems & Gemology." + - doi: "10.5741/gems.18.4.186" + citation: "Keller (1982) The Chanthaburi-Trat Gem Field, Thailand. Gems & Gemology." + - doi: "10.15506/jog.2019.36.7.634" + citation: "Promwongnan & Sutthirat (2019) Mineral Inclusions in Ruby from Bo Rai, Trat Province. Journal of Gemmology." + - doi: "10.1016/j.jseaes.2018.07.006" + citation: "Sutthirat et al. (2018) Mantle and deep crustal xenoliths in basalts, Bo Rai ruby deposit. Journal of Asian Earth Sciences." + - doi: "10.5741/gems.55.4.536" + citation: "Palke et al. (2019) Geographic Origin Determination of Blue Sapphire. Gems & Gemology." diff --git a/docs/learn/origin/thailand/sapphire.yaml b/docs/learn/origin/thailand/sapphire.yaml new file mode 100644 index 0000000..fa2020a --- /dev/null +++ b/docs/learn/origin/thailand/sapphire.yaml @@ -0,0 +1,130 @@ +title: Thai Sapphire — Bo Phloi and Kanchanaburi Types +description: Basaltic high-Fe blue sapphire from Bo Phloi and Kanchanaburi; strong 450/460/470 nm iron triplet, common heat treatment, basalt-suite inclusions. +order: 3 +category: origin +subcategory: thailand +difficulty: advanced +icon: gem +related: + - origin/thailand/overview + - origin/thailand/ruby + - origin/cambodia + - origin/kashmir + - origin/ceylon + - species/corundum +tags: + - thailand + - sapphire + - bo-phloi + - kanchanaburi + - basaltic + - corundum + +sections: + - title: Introduction + content: | + Thai sapphire from the Bo Phloi district (Kanchanaburi Province) and surrounding + areas represents a classically basaltic, high-iron corundum type. Bo Phloi sapphires + were historically among Southeast Asia's most important blue sapphires and are + scientifically well-characterised. Commercial production is largely concluded but + the material remains a reference point for basaltic sapphire identification. + + - title: Colour Range + content: | + Thai basaltic sapphires display a wider colour range than marble-hosted sapphires: + + - **Blue**: Predominant; dark to very dark blue-green; often described as "inky" + - **Yellow**: Common in Bo Phloi; golden to greenish-yellow + - **Green**: Blue-green to green from high Fe content + - **Black star**: Star sapphire with opaque body + - **Golden star**: Asterism in yellowish material + + The very dark tone of Thai blue sapphires — often darker than Kashmir or Ceylon — + results from the combined effect of high-Fe absorption across the visible spectrum. + + - title: Diagnostic Inclusions + content: | + Khamloet et al. (2014) identified two groups of mineral inclusions from Bo Phloi: + subsections: + - title: Felsic Alkaline Suite + content: | + - Alkali feldspar (orthoclase/sanidine) + - Nepheline (feldspathoid) + - Sapphirine (deep crustal / high-P indicator) + - Biotite-phlogopite mica + + - title: Contact-Metamorphic Suite + content: | + - Hercynitic spinel (dark, opaque) + - Zircon crystals — common; often with radiation damage halos + - Manganiferous ilmenite (black opaque) + - Silica-rich enstatite (pyroxene) + - Almandine-pyrope garnet + - Staurolite + - Calcite (occasional — from xenolith material) + - Monazite (rare, distinctive) + + - title: Inclusion Significance + callout: + type: tip + title: Nepheline and Hercynitic Spinel + text: | + Nepheline (a feldspathoid, chemically distinct from feldspar) and hercynitic + spinel inclusions in sapphire are strongly associated with basaltic-hosted + corundum in a high-alkalinity magmatic environment. Their presence helps confirm + basaltic rather than metamorphic or pegmatitic origin. + + Zircon with radiation halos is extremely common in Thai and Cambodian basaltic + sapphire and is a reliable pointer to basaltic parentage. + + - title: Spectroscopic Properties + content: | + Characteristic UV-Vis features of Thai blue sapphire: + subsections: + - title: Iron Triplet + content: | + - Strong absorption at approximately 450, 460, and 470 nm (Fe²⁺–Ti⁴⁺ charge + transfer + Fe–Fe intervalence) + - This triplet is significantly stronger than in Kashmir or Ceylon sapphire + - The triplet contributes to the "steely" or "inky" dark tone + - Similar in strength to Cambodian material but distinct from Kashmir's velvety blue + + - title: Fluorescence + content: | + - LWUV fluorescence: Inert to very weak + - High iron strongly suppresses any fluorescence + - Contrast with Kashmir sapphire: moderate chalky blue fluorescence + - Contrast with some Ceylon material: variable blue-white fluorescence + + - title: Origin Determination by LA-ICP-MS + content: | + Chemical separation of Thai sapphire from other basaltic sources: + + - **High Fe, high Ti**: Primary geochemical signature of basaltic parentage + - **Ga/Mg ratio**: Basaltic sapphires have elevated Ga and different Mg profiles + vs marble-hosted material + - **Fe/Ti discrimination**: Separates Thai from Cambodian (subtle difference), + and both from Kashmir, Ceylon, and Australian + - No rutile silk of the Kashmir type + - No calcite of the marble-hosted type + + - title: Heat Treatment + callout: + type: warning + title: Treatment Is the Norm + text: | + The overwhelming majority of Thai blue sapphire in the trade is heat-treated. + Chanthaburi and Bangkok pioneered the technology for heating corundum to dissolve + rutile silk and improve colour. Unheated Thai sapphire is uncommon and carries + little origin premium. + + After heating, Thai sapphires may lose some diagnostic inclusions (silk dissolves) + but the trace element signature and fluorescence inertness remain diagnostic. + +sources: + - doi: "10.1016/j.rgg.2014.08.004" + citation: "Khamloet, Pisutha-Arnond & Sutthirat (2014) Mineral inclusions in sapphire, Bo Phloi, Kanchanaburi. Russian Geology and Geophysics." + - doi: "10.1016/j.jseaes.2019.104068" + citation: "Sutthirat et al. (2019) Multistages of sapphire formation, Bo Phloi basaltic gem field. Journal of Asian Earth Sciences." + - doi: "10.5741/gems.55.4.536" + citation: "Palke et al. (2019) Geographic Origin Determination of Blue Sapphire. Gems & Gemology." diff --git a/docs/learn/origin/thailand/zircon.yaml b/docs/learn/origin/thailand/zircon.yaml new file mode 100644 index 0000000..10eee15 --- /dev/null +++ b/docs/learn/origin/thailand/zircon.yaml @@ -0,0 +1,105 @@ +title: Thai Blue Zircon — Heat-Treatment Hub +description: Thailand as the global centre for heat-treating Cambodian and Vietnamese zircon rough into blue zircon; origin, treatment process, and identification. +order: 4 +category: origin +subcategory: thailand +difficulty: intermediate +icon: gem +related: + - origin/thailand/overview + - origin/cambodia + - species/zircon +tags: + - thailand + - zircon + - blue-zircon + - heat-treatment + - chanthaburi + +sections: + - title: Introduction + content: | + Thailand — primarily Chanthaburi and Bangkok — is the world's dominant centre + for the production of faceted blue zircon. The majority of blue zircon on the + market has not been mined in Thailand but has been heat-treated there: brownish + to colourless zircon rough from Cambodia and Vietnam is imported and heated to + produce the prized blue colour. + + - title: Why Thailand Treats Zircon + content: | + Thailand's role in the zircon trade: + + - Chanthaburi has operated as Southeast Asia's gem processing centre since the + 1970s; corundum heating infrastructure and expertise extend naturally to zircon + - Cambodian zircon from Ratanakiri Province and Vietnamese deposits supply most + of the rough + - Low-cost, high-volume treatment capacity allows Thailand to handle bulk supply + - Finished blue zircon is exported globally through Bangkok gem dealers + + - title: The Heat-Treatment Process + content: | + Converting brownish or colourless zircon to blue: + subsections: + - title: Mechanism + content: | + - Brownish zircon owes its colour partly to radiation damage (metamict zones) + and partly to charge-transfer absorption related to Fe and other trace elements + - Heating at 900–1000°C in an OXIDISING atmosphere (air or with oxidising agents) + anneals radiation damage and changes the valence state of iron and other + chromophores, producing the characteristic blue-green colour + - The blue is not caused by a single chromophore but by a combination of + charge-transfer mechanisms in the heated zircon structure + + - title: Colour Results + content: | + - **Blue to blue-green**: The primary commercial goal — the classic "blue zircon" + - **Colourless**: Some rough heats to colourless (diamond simulant use) + - **Golden to orange**: Produced by heating in reducing conditions (less common) + - **Colour stability**: Blue zircon colour can fade slightly in strong light over + time but is generally stable under normal conditions + + - title: Zircon Identification Essentials + table: + headers: + - Property + - Value / Description + rows: + - ["Composition", "ZrSiO₄ (zirconium silicate)"] + - ["RI", "1.925–1.984 (high, uniaxial positive); birefringence up to 0.059"] + - ["SG", "4.67–4.70 (high)"] + - ["Hardness", "7–7.5"] + - ["Dispersion", "0.038 (B–G interval; high fire)"] + - ["Crystal system", "Tetragonal; uniaxial positive"] + - ["Key test", "High SG; strong doubling of back facets at 10x"] + + - title: Doubling of Facets + callout: + type: tip + title: The Doubling Diagnostic + text: | + High birefringence in blue zircon causes STRONG DOUBLING of back facets when + viewed through the table at 10× magnification. This is one of the most reliable + field-level diagnostics for zircon and distinguishes it from aquamarine (low DR), + blue topaz (low DR), and tanzanite (moderate DR but different appearance). + + The doubling effect is especially clear in blue zircon due to the stone's high + RI and refractive index contrast. + + - title: Distinguishing Thai-Treated Zircon + content: | + Treatment and origin notes: + + - Virtually all commercial blue zircon is heat-treated; untreated blue zircon + from primary sources is extremely rare + - Treatment is accepted and standard; laboratories report it as "Evidence of + heat treatment" on origin reports + - Chemical origin determination of zircon (Cambodia vs Vietnam vs elsewhere) + uses U-Pb age dating and trace element profiles — not routine in the gem trade + - "Thai blue zircon" as a label refers to the treatment location, not the mining + origin of the rough + +sources: + - doi: "10.5741/gems.18.4.186" + citation: "Keller (1982) The Chanthaburi-Trat Gem Field, Thailand. Gems & Gemology." + - doi: "10.5741/gems.45.4.236" + citation: "Shor & Weldon (2009) Ruby and Sapphire Production and Distribution: A Quarter Century of Change. Gems & Gemology." diff --git a/docs/learn/origin/usa/montana-sapphire.yaml b/docs/learn/origin/usa/montana-sapphire.yaml new file mode 100644 index 0000000..3319040 --- /dev/null +++ b/docs/learn/origin/usa/montana-sapphire.yaml @@ -0,0 +1,130 @@ +title: Montana Sapphire — Yogo Gulch, Rock Creek, Missouri River +description: Yogo Gulch steely-blue lamprophyre sapphire (no heat needed), Rock Creek and Missouri River alluvial pastels; distinct Fe/Ti/Mg trace element chemistry; US commercial significance. +order: 2 +category: origin +subcategory: usa +difficulty: advanced +icon: gem +related: + - origin/usa/overview + - origin/ceylon + - origin/thailand/sapphire + - species/corundum +tags: + - usa + - montana + - yogo-gulch + - rock-creek + - missouri-river + - sapphire + - lamprophyre + - corundum + - origin/usa + +sections: + - title: Introduction + content: | + Montana is the principal sapphire state in the USA, with three distinct deposit + types producing gemstones of different character. Yogo Gulch, discovered in 1895, + produces the most distinctive sapphires — a steely to cornflower blue that rarely + requires heat treatment. Rock Creek and the Missouri River deposits supply a broader + colour range, most of which is heat-treated for commercial blue. + + - title: Yogo Gulch — The Defining Montana Deposit + content: | + Yogo Gulch sapphire characteristics: + subsections: + - title: Geology + content: | + - Hosted in a **lamprophyre dike** (alkalic intrusive) cutting Palaeozoic + carbonate host rocks at ~500 m depth in Judith Basin County, central Montana + - Palke, Renfro, and Berg (2016) investigated the lamprophyre host and melt + inclusions: Yogo is geologically related to subduction-related alkalic magmatism + - Palke et al. (2018) documented a geochemical link: "A common origin for + Thai/Cambodian rubies and blue and violet sapphires from Yogo Gulch, Montana" + — both derive from subduction-related alkalic magmas, though Yogo's chemistry + differs in detail + + - title: Colour + content: | + - **Steely blue to violet-blue**: Uniform, even saturation throughout — rarely + shows colour zoning + - Compared to Kashmir: steelier, less "velvety"; more uniform but less silky + - No colour change; no parti-colour + - **Distinctive uniformity**: Renfro et al. (2018) noted that "virtually all + of the material produced has a desirable even blue to violet or purple" + + - title: Size and Heat Treatment + content: | + - Almost never exceeds 2 ct faceted; the vast majority are ≤0.5 ct + - Flat, tabular crystal habit gives very low cutting yield — explains rarity + of larger stones + - **No heat treatment needed**: Low Fe content means little silk or rutile + to dissolve; Yogo stones appear similar heated or unheated — historically + treated as unnecessary and rarely performed + - This "naturally heat-treatment-free" quality is unusual for a sapphire + with any basaltic/lamprophyre association + + - title: Trace Element Chemistry + content: | + - **Relatively low Fe** compared to Thai/Cambodian basaltic sapphire — + explains the clear blue rather than dark greenish-blue inky tone + - **Low Cr** — no Cr lines; pure Fe-Ti coloration + - Krebs et al. (2020) demonstrated that Montana sapphires can be separated + from Asian basaltic sapphires using Ga/Mg, Fe/Ti, and Cr/Ga ratios; Yogo + shows distinctively low Fe and low Cr/Ga + + - title: Inclusions + content: | + - Few inclusions; characteristic lack of silk (rutile needles) — unusual + for a basalt/lamprophyre associated sapphire + - Irregular liquid-filled cavities; two-phase inclusions + - No marble-suite inclusions + + - title: Rock Creek and Missouri River + content: | + Other Montana sapphire deposits: + subsections: + - title: Rock Creek + content: | + - Alluvial deposits (gravel bars) in Granite County (Philipsburg area) + - Palaeodrainage system; primary host debated (may be lamprophyre-related) + - **Wide colour range**: colourless, pale blue, pale green, yellow, orange, + pink, and parti-colour + - Most material is heat-treated commercially to produce market-acceptable + blue; post-treatment may resemble Ceylon or Australian sapphire + - Pastel and parti-colour character without heat distinguishes from most + commercial sources + + - title: Missouri River + content: | + - Near Havre, northern Montana; alluvial gravels + - **Diverse pastel colours**: Same palette as Rock Creek + - Heavily mined in the early 20th century for watch-bearing abrasives + (industrial use) before gem interest developed + - Commercial production continues; heat-treated blue is the dominant product + + - title: Origin Separation from Asian Basaltic Sapphire + table: + headers: + - Feature + - Yogo Gulch (Montana) + - Thai / Cambodian Basaltic + rows: + - ["Fe content", "Relatively low", "High (>600–1,000 ppm)"] + - ["450–470 nm triplet", "Moderate", "Very strong"] + - ["LWUV fluorescence", "Inert to weak", "Inert"] + - ["Heat treatment needed", "No (Yogo)", "Usually yes"] + - ["Crystal habit", "Flat tabular; low yield", "Rounded alluvial pebbles"] + - ["Geological host", "Lamprophyre dike", "Cenozoic alkali basalt"] + - ["Cr/Ga ratio", "Distinctively low (Krebs 2020)", "Higher"] + +sources: + - doi: "10.5741/gems.54.2.184" + citation: "Renfro, Palke & Berg (2018) Gemological Characterization of Sapphires from Yogo Gulch, Montana. Gems & Gemology." + - doi: "10.1016/j.lithos.2016.06.004" + citation: "Palke, Renfro & Berg (2016) Origin of sapphires from Yogo Gulch, Montana. Lithos." + - doi: "10.2138/am-2018-6164" + citation: "Palke et al. (2018) Common origin for Thai/Cambodian rubies and Yogo Gulch sapphires. American Mineralogist." + - doi: "10.3390/min10050447" + citation: "Krebs et al. (2020) Expanded trace element suite plus Sr-Pb isotopes for ruby and sapphire origin. Minerals." diff --git a/docs/learn/origin/usa/overview.yaml b/docs/learn/origin/usa/overview.yaml new file mode 100644 index 0000000..ec99caf --- /dev/null +++ b/docs/learn/origin/usa/overview.yaml @@ -0,0 +1,112 @@ +title: USA — Gem Origins Overview +description: US gem deposits — Montana sapphire, Utah red beryl, Arizona peridot, California and Maine tourmaline; geologically diverse patchwork provinces. +order: 1 +category: origin +subcategory: usa +difficulty: intermediate +icon: gem +related: + - origin/overview + - origin/usa/montana-sapphire + - origin/usa/utah-red-beryl + - species/corundum + - species/beryl +tags: + - usa + - montana + - utah + - arizona + - california + - sapphire + - red-beryl + - peridot + - origin/usa + +sections: + - title: Introduction + content: | + The United States hosts geologically diverse gem deposits with no single dominant + orogenic province. Major deposits include: Montana sapphire (lamprophyre and + alluvial), Utah red beryl (rhyolitic volcanic), Arizona peridot (basaltic xenocyrst), + and California/Maine tourmaline (LCT pegmatite). Each deposit reflects a distinct + geological setting; no common chemical or inclusion fingerprint links them. + + - title: Major US Gem Deposits + table: + headers: + - State + - Deposit + - Host Rock + - Gems + rows: + - ["Montana", "Yogo Gulch, Rock Creek, Missouri River", "Lamprophyre dike + alluvial placers", "Sapphire"] + - ["Utah", "Wah Wah Mountains", "Topaz rhyolite (Eocene)", "Red beryl"] + - ["Arizona", "San Carlos Apache Reservation", "Quaternary alkali basalt (xenocryst)", "Peridot"] + - ["California", "Pala District, San Diego County", "Cretaceous LCT pegmatite", "Elbaite tourmaline"] + - ["Maine", "Oxford County pegmatites", "LCT granite pegmatite", "Elbaite tourmaline (blue/green)"] + + - title: Montana Sapphire — Brief Overview + content: | + - Three deposit types: Yogo Gulch (lamprophyre), Rock Creek (alluvial), Missouri River + - Yogo: steely blue, rarely >2 ct, no heat treatment needed; low Fe; lamprophyre host + - Rock Creek / Missouri River: pastel multicolour; mostly heat-treated for commercial blue + - See dedicated file: origin/usa/montana-sapphire + + - title: Utah Red Beryl — Brief Overview + content: | + - Wah Wah Mountains, Beaver County — the world's only commercial red beryl source + - Hosted in Eocene topaz rhyolite; Mn³⁺ chromophore; typically <0.5 ct + - See dedicated file: origin/usa/utah-red-beryl + + - title: Arizona Peridot — San Carlos + content: | + San Carlos Apache Reservation (Gila County) produces an estimated 80–95% of + commercial peridot by volume: + + - **Host**: Quaternary alkali basalt; peridot is a mantle xenocryst + - **Composition**: Mg₂SiO₄–Fe₂SiO₄ (olivine); San Carlos material ~Fo₈₆–Fo₉₂ + - **Properties**: RI 1.654–1.712 (α–γ); biaxial positive; birefringence 0.035–0.038 + (strong facet doubling at 10×); SG 3.28–3.48; Hardness 6.5–7 + - **Colour**: Yellow-green to lime-green (Fe²⁺ chromophore) + - **Absorption**: Three-banded iron spectrum: 493, 473, 453 nm (Foundation examination requirement) + - **Key inclusions**: Chromite (spinel) with lily-pad tension fracture halos (Diploma + requirement); ludwigite platelets; biotite; fluid inclusions + - **Origin discrimination**: Not practical at bench level; San Carlos vs Hawaiian or + Chinese peridot requires quantitative microprobe analysis + + - title: US Tourmaline (Brief) + content: | + California (Pala District) and Maine (Oxford County) tourmaline: + + - Both produce elbaite (Na(Li,Al)₃Al₆(Si₆O₁₈)(BO₃)₃(OH)₄) from LCT-type pegmatites + - Colour range: pink/red rubellite, blue indicolite, bicolour, watermelon, parti + - RI: 1.614–1.679 (uniaxial negative); SG: 3.01–3.06; birefringence: 0.014–0.021 + - California: historical Qing Dynasty export; Maine: first commercial North American tourmaline + - Discrimination between California and Maine deposits, and between US and other + tourmaline origins, is a laboratory-level task requiring trace element chemistry + + - title: US Tourmaline and Arkansas Diamond — Notes + callout: + type: info + title: CITATION NEEDED Items + text: | + Two US gem localities cannot be described with specific origin diagnostics in + this curriculum because no peer-reviewed gemmological discrimination paper + was retrieved: + + 1. US TOURMALINE sub-deposit distinction (Maine vs California): No specific + inter-deposit discrimination paper retrieved — [CITATION NEEDED]. + Include as brief item only without diagnostic claims. + + 2. ARKANSAS DIAMOND (Crater of Diamonds, Murfreesboro): Lamproite-hosted; + educational "finders-keepers" site; negligible commercial production. + No peer-reviewed gemological characterisation retrieved — [CITATION NEEDED]. + Mention only as educational context; do not assign gemmological diagnostics. + +sources: + - doi: "10.5741/gems.54.2.184" + citation: "Renfro, Palke & Berg (2018) Gemological Characterization of Yogo Gulch Sapphires. Gems & Gemology." + - doi: "10.5741/gems.20.4.208" + citation: "Shigley & Foord (1984) Red Beryl, Wah Wah Mountains, Utah. Gems & Gemology." + - doi: "10.5741/gems.17.4.205" + citation: "Koivula (1981) San Carlos peridot. Gems & Gemology." diff --git a/docs/learn/origin/usa/utah-red-beryl.yaml b/docs/learn/origin/usa/utah-red-beryl.yaml new file mode 100644 index 0000000..5eee682 --- /dev/null +++ b/docs/learn/origin/usa/utah-red-beryl.yaml @@ -0,0 +1,128 @@ +title: Utah Red Beryl — Wah Wah Mountains +description: World's only commercial red beryl source — Mn³⁺-coloured beryl in Eocene topaz rhyolite, Wah Wah Mountains, Utah; properties, inclusions, market rarity. +order: 3 +category: origin +subcategory: usa +difficulty: advanced +icon: gem +related: + - origin/usa/overview + - species/beryl +tags: + - usa + - utah + - wah-wah-mountains + - red-beryl + - bixbite + - manganese + - rhyolite + - origin/usa + +sections: + - title: Introduction + content: | + Red beryl — commercially known as "bixbite" (though this trade name overlaps with + the manganese oxide mineral bixbyite, causing confusion) — is arguably the rarest + gem-quality beryl variety. Commercial production occurs at essentially one location + in the world: the Wah Wah Mountains of Beaver County, Utah. Shigley and Foord (1984) + provided the definitive characterisation: stones occupy "vugs and fractures in a + topaz rhyolite" — a uniquely volcanic gem beryl occurrence. + + - title: Geological Setting + content: | + Wah Wah Mountains red beryl geology: + + - **Host rock**: Topaz rhyolite — a silica-rich, F-bearing volcanic flow — of + Eocene age (~20–19 Ma), formed during Basin and Range extensional tectonics + - **Formation mechanism**: Beryl crystallises from an F-rich hydrothermal/vapour + phase generated during cooling of the rhyolitic magma; this vapour phase + penetrates vugs and fractures in the volcanic rock + - **Uniqueness**: This is one of very few documented cases of gem beryl forming + in a purely volcanic (rhyolitic) setting rather than the usual pegmatitic or + contact-metamorphic environment + - Additional observations on crystal morphology documented by later Journal of + Gemmology work + + - title: Colour and Chromophore + content: | + Red beryl colour origin: + + - **Colour**: Raspberry red to pink-red, purplish-red; the colour range is + consistent but saturation varies + - **Chromophore**: Mn³⁺ substituting Al³⁺ in the beryl structure + - Mn³⁺ absorption band in the ~490–560 nm region gives the red colour by + absorbing blue-green light — the complement of red + - This is fundamentally different from the Cr³⁺ colouring of ruby or emerald + + - title: Properties + table: + headers: + - Property + - Value + rows: + - ["Formula", "Be₃Al₂Si₆O₁₈ (beryl), Mn³⁺ colouring"] + - ["Crystal system", "Hexagonal; uniaxial negative"] + - ["RI", "1.564–1.584 (ne); 1.568–1.590 (no); DR ~0.006"] + - ["SG", "2.66–2.70"] + - ["Hardness", "7.5–8 (Mohs)"] + - ["Crystal habit", "Tabular to short hexagonal prisms; very small"] + - ["Typical size", "≤2 ct cut; usually <0.5 ct; >1 ct exceptional"] + - ["Fluorescence", "Generally inert"] + + - title: Inclusions + content: | + Inclusions found in Utah red beryl: + + - **Two-phase inclusions**: Liquid + gas + - **Growth tubes**: Parallel to the c-axis + - **Topaz crystals**: From the same rhyolitic host — geologically associate + - **Bixbyite crystals**: Iron-manganese oxide; small black cuboids + - **Hematite**: Iron oxide + - **Needle-like inclusions**: Occasionally present + + - title: Distinguishing Red Beryl + content: | + Key separations from simulants and similar gems: + subsections: + - title: From Red Spinel + content: | + - Red spinel is isotropic (cubic); red beryl is uniaxial negative (hexagonal) + - On polariscope: spinel SR, red beryl DR + - SG differs: spinel ~3.60; red beryl ~2.67 — major difference + - RI differs: spinel 1.712–1.736; red beryl 1.564–1.590 + + - title: From Rubellite (Red Tourmaline) + content: | + - Both are DR (doubly refractive) and red + - SG: rubellite ~3.02; red beryl ~2.67 + - RI: rubellite ~1.614–1.679; red beryl ~1.564–1.590 (lower) + - Birefringence: rubellite 0.014–0.021; red beryl ~0.006 (lower) + - Pleochroism: rubellite dichroic (deep pink / pale pink); red beryl + pleochroism less dramatic for red material + + - title: From Red Glass + content: | + - Glass is isotropic; red beryl is doubly refractive — polariscope separation + - SG of glass varies but usually 2.3–4.5; red beryl SG is characteristic + - Chelsea filter and spectrum may help confirm beryl species + + - title: Rarity and Market + callout: + type: info + title: Extreme Rarity + text: | + Red beryl is sometimes cited as approximately 1,000 times rarer than emerald + by weight mined. The extremely small crystal size means faceted stones are almost + always under 1 ct; stones above 3 ct are collector rarities commanding exceptional + prices. + + The Wah Wah Mountains deposit (Ruby Violet Claims / Violet Claims mine) is + the only significant source globally. Occasional red beryl has been reported + in the Paramount Canyon and Round Mountain areas of New Mexico, but no commercial + production has been established. + +sources: + - doi: "10.5741/gems.20.4.208" + citation: "Shigley & Foord (1984) Red Beryl from the Wah Wah Mountains, Utah. Gems & Gemology." + - doi: "10.15506/jog.1993.23.7.409" + citation: "Journal of Gemmology (1993) Red beryl crystal morphology observations." diff --git a/docs/learn/origin/vietnam.yaml b/docs/learn/origin/vietnam.yaml new file mode 100644 index 0000000..bb433f5 --- /dev/null +++ b/docs/learn/origin/vietnam.yaml @@ -0,0 +1,157 @@ +title: Vietnam — Luc Yen Ruby and Cobalt-Blue Spinel +description: Marble-hosted ruby and spinel from Luc Yen (Yen Bai) and Quy Chau; low-Fe high-Cr chemistry, cobalt-blue spinel, distinction from Burmese material. +order: 11 +category: origin +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/burma/ruby + - origin/burma/spinel + - origin/tajikistan + - species/corundum + - species/spinel +tags: + - vietnam + - luc-yen + - yen-bai + - quy-chau + - ruby + - spinel + - marble-hosted + - cobalt-blue + - origin/vietnam + +sections: + - title: Introduction + content: | + Vietnam's northern gem provinces rank among the world's most important marble-hosted + corundum and spinel sources. The Luc Yen district (Yen Bai Province) and Quy Chau + (Nghe An Province) produce ruby and spinel in a geological setting analogous to + Mogok, Burma: Himalayan-related metamorphism of carbonate-platform sequences yielded + gem-quality corundum and spinel in marble. Vietnam also hosts the world's leading + source of cobalt-blue spinel — a unique and highly prized material. + + - title: Geological Context + content: | + Marble-hosted gem formation in northern Vietnam: + subsections: + - title: Luc Yen District + content: | + - Located in Yen Bai Province; the carbonate platforms were subjected to + "intense metamorphism during successive orogenies" in the Red River shear zone + - Marble-hosted genesis analogous to Mogok (Burma): gems crystallised in + metamorphosed limestone during Himalayan-related orogenic events + - Produces ruby, pink spinel, blue spinel, sapphire, moonstone, and tourmaline + + - title: Quy Chau + content: | + - Central Vietnam; Nghe An Province + - First deposits opened to international buyers after Vietnam's economic + reform (doi moi) in 1987 + - Marble-hosted ruby; historically the entry point for Vietnamese rubies + into the international market + + - title: Ruby — Luc Yen and Quy Chau Types + content: | + Characteristics of Vietnamese marble-hosted ruby: + subsections: + - title: Colour and Appearance + content: | + - Vivid pinkish-red to red; can approach Mogok quality + - Often lighter and more saturated than Thai basaltic ruby; some with + slight pinkish or purplish modifiers + - Typically lower clarity than Mogok material — much production is cabochon + or star quality + + - title: Diagnostic Inclusions + content: | + - **Calcite rhombs**: Marble-hosted environment; characteristic of all + marble-type corundum globally + - **Pyrrhotite**: Iron sulfide crystals — highly diagnostic for Luc Yen + - **Nordstrandite**: Rare aluminium hydroxide mineral; documented in Luc Yen + ruby by Kane et al. (1991) — very unusual in corundum globally + - **Bluish colour zones and angular growth features**: Characteristic of + Vietnamese marble ruby + - **Fluid inclusions**: CO₂-rich primary inclusions with multi-solid residues; + brine compositions differ from Mogok in specific salt assemblage + + - title: Spectroscopy and Fluorescence + content: | + - **LWUV fluorescence**: Strong red — critical contrast with Thai/Cambodian + basaltic rubies where iron quenches fluorescence + - **Low Fe**: Marble-hosted chemistry; typically <300 ppm Fe by LA-ICP-MS + - **High Cr**: Dominant chromophore; similar principle to Mogok + + - title: Nordstrandite and Pyrrhotite + callout: + type: tip + title: Diagnostic Combination for Luc Yen + text: | + The combination of NORDSTRANDITE (aluminium hydroxide) and PYRRHOTITE (iron + sulfide) in the inclusion suite, alongside calcite rhombs and strong red LWUV + fluorescence, is highly characteristic of Luc Yen ruby origin. Nordstrandite + is exceptionally rare as a gemstone inclusion globally. + + - title: Distinguishing Vietnam from Burma (Mogok) + table: + headers: + - Feature + - Luc Yen (Vietnam) + - Mogok (Burma) + rows: + - ["Fe content", "Low (<300 ppm)", "Low (<300 ppm)"] + - ["LWUV fluorescence", "Strong red", "Strong red"] + - ["Key inclusions", "Pyrrhotite, nordstrandite, calcite", "Calcite, apatite, sphene, silk"] + - ["Ga/Mg ratio", "Relatively higher Ga", "Lower Ga — lab criterion"] + - ["Colour zones", "Bluish zones, angular features", "Irregular; treacle swirls"] + - ["Fluorescence nuance", "Strong red (similar to Mogok)", "Strong red (benchmark)"] + - ["Lab separation", "LA-ICP-MS Ga/Mg + inclusions", "Reference standard"] + + - title: Spinel — Cobalt-Blue Luc Yen Type + content: | + Vietnam's most celebrated and distinctive gem material: + subsections: + - title: Cobalt-Blue Spinel + content: | + - Luc Yen is the world's leading source of vivid blue spinel coloured by Co²⁺ + - Co²⁺ substitution is rare in spinel globally; most blue spinel is Fe-coloured + - Chauviré et al. (2015) established that the blue "is due to cobalt (Co²⁺), + with some iron contribution" — a marble metamorphic genesis + - UV-Vis spectroscopy: Cobalt produces three characteristic absorption bands; + the Co²⁺ spectrum is distinctive from Fe-coloured blue spinel + + - title: Red and Pink Spinel + content: | + - Full colour range: vivid red, pink, orange, lavender, purple + - Trace element variation within Luc Yen: Cong Troi sub-deposit has low Zn + (<500 ppm); An Phu spinels are Zn-rich (up to 11,000 ppm) + - Titanite inclusions and dislocation systems are Luc Yen-specific features + that differ from Mogok (apatite, calcite, octahedral negative crystals) and + from Kuh-i-Lal/Tajikistan (different Ti, Ni, Zn, Sn profiles) + + - title: Spinel Origin Determination + content: | + Separating Luc Yen spinel from Mogok and Kuh-i-Lal: + + - **Co²⁺ blue**: Confirmed by UV-Vis and LA-ICP-MS cobalt content; no other + major spinel source produces commercially significant cobalt-blue material + - **Trace element profile**: Ti, Fe, Ni, Zn, Zr, Sn ratios differ between + Luc Yen, Mogok, and Kuh-i-Lal; Malsy & Klemm (2010) demonstrated this separation + - **Titanite inclusions**: Diagnostic for Luc Yen; absent in Mogok and Kuh-i-Lal + - **Mn/Ti plot + Cr+V**: Chemical discrimination from Mn/Ti vs Cr+V is applicable + to spinel from these Himalayan-belt sources + +sources: + - doi: "10.5741/gems.27.3.136" + citation: "Kane et al. (1991) Rubies and Fancy Sapphires from Vietnam. Gems & Gemology." + - doi: "10.5741/gems.48.3.158" + citation: "Le Thi-Thu Huong et al. (2012) Gemstones from Vietnam: An Update. Gems & Gemology." + - doi: "10.5741/gems.51.1.2" + citation: "Chauviré et al. (2015) Blue Spinel from the Luc Yen District of Vietnam. Gems & Gemology." + - doi: "10.15625/0866-7187/40/2/12241" + citation: "Pham Van Long et al. (2018) Trace elements and oxygen isotopes of gem spinels from Luc Yen–An Phu. Vietnam Journal of Earth Sciences." + - doi: "10.2533/chimia.2010.741" + citation: "Malsy & Klemm (2010) Distinction of Gem Spinels from the Himalayan Mountain Belt. CHIMIA." + - doi: "10.1127/ejm/2015/0027-2442" + citation: "Giuliani et al. (2015) Fluid inclusions in ruby from Asian marble deposits. European Journal of Mineralogy." diff --git a/docs/learn/origin/zimbabwe.yaml b/docs/learn/origin/zimbabwe.yaml new file mode 100644 index 0000000..226eb5e --- /dev/null +++ b/docs/learn/origin/zimbabwe.yaml @@ -0,0 +1,167 @@ +title: Zimbabwe — Sandawana Emerald and Marange Diamond +description: Sandawana (Belingwe) emerald — vivid Cr-rich, tremolite inclusions, very small; Marange alluvial diamond; Murehwa chrysoberyl [CITATION NEEDED]. +order: 21 +category: origin +difficulty: advanced +icon: gem +related: + - origin/overview + - origin/zambia + - origin/colombia + - origin/russia/emerald + - species/emerald +tags: + - zimbabwe + - sandawana + - belingwe + - emerald + - marange + - diamond + - tremolite + - origin/zimbabwe + +sections: + - title: Introduction + content: | + Zimbabwe hosts two internationally significant gem deposits: Sandawana emerald from + the Belingwe (Mberengwa) district — known for its exceptionally saturated small + crystals — and the Marange alluvial diamond field (Manicaland Province), which + became controversial due to human rights concerns. Sandawana is the more important + gemmological reference deposit; Marange is commercially significant but gemmologically + less characterised in peer-reviewed literature. + + - title: Sandawana Emerald — Overview + content: | + The defining characteristics of Sandawana: + subsections: + - title: Discovery and History + content: | + - Sandawana Mine (Belingwe/Mberengwa district, Midlands Province); mining + established by the early 1950s; the name derives from the local Karanga word + - Gained international attention from the 1960s for intensely saturated crystals + - Zwaan, Kanis, and Petsch (1997): "an intensely saturated, pure green colour + comparable to Colombian emerald, but they are generally small" + + - title: Geological Setting + content: | + - Hosted in **ultramafic rocks** (talc-chlorite-carbonate schists derived from + serpentinite) of the Belingwe greenstone belt; at the contact with granitic + intrusions + - Emerald in **talc-carbonate veins** and chlorite-schist envelopes around + quartz veins; Cr from the ultramafic host; Be from the granite + - **Oxygen isotope study** (2004): Confirmed a fluid-mixing genesis at the + schist-granite contact; meteoric + magmatic/metamorphic fluid mixing + + - title: Sandawana Colour and Fluorescence + content: | + Optical characteristics: + + - **Colour**: Vivid, pure grass-green to emerald-green; colour saturation among + the highest of any natural emerald; often described as "vivid green" without + blue modifiers — the emerald equivalent of "pigeon blood" quality + - **Chromophores**: Cr³⁺ dominant; minimal V; very low Fe — the low Fe is the + key to the exceptional colour purity and very strong red fluorescence + - **UV Fluorescence (LWUV)**: Very strong red — one of the highest Cr-driven + fluorescence intensities among natural emeralds; significantly stronger than + Zambian (higher Fe) or Colombian material + - **Chelsea Colour Filter**: Strong red (Cr dominant) + - **Size constraint**: Almost invariably <0.5 ct commercial material; 0.1–0.3 ct + typical; stones >1 ct are exceptional and command premium prices + + - title: Diagnostic Inclusions — Tremolite Needles + callout: + type: tip + title: Tremolite as the Primary Diagnostic + text: | + TREMOLITE NEEDLES (calcium magnesium amphibole) are the primary diagnostic + inclusion for Sandawana origin — as confirmed by Zwaan and Burke (1998) using + Raman microspectroscopy. These are straight, slender, colourless to pale needles, + often in parallel groups. + + Tremolite distinguishes Sandawana from: + - COLOMBIAN emerald (pyrite/parisite/calcite) + - URAL Russian emerald (phlogopite mica platelets) + - ZAMBIAN emerald (biotite mica, not tremolite; different texture) + - ETHIOPIAN Shakiso (tremolite also present but with more phlogopite) + + - title: Additional Sandawana Inclusions + content: | + Complete inclusion suite: + + - Talc (soft, platy) — from the talc-schist host + - Chlorite flakes + - Dolomite and calcite rhombs + - Two-phase fluid inclusions (liquid + gas) + - Apatite (rounded crystals) + + - title: Sandawana Origin Determination + content: | + Combination criteria virtually diagnostic for Sandawana: + + 1. **Very high Cr with very low Fe**: High Cr/Fe ratio contrasts with Zambian + and Brazilian material; LA-ICP-MS is confirmatory + 2. **Tremolite needle inclusions**: Primary visual diagnostic (Zwaan & Burke 1998) + 3. **Very small crystal size**: <0.5 ct in virtually all commercial material + 4. **Strong red LWUV fluorescence**: Very strong — much stronger than most other + emerald origins at equivalent saturation + + - title: Sandawana vs Key Emerald Origins + table: + headers: + - Feature + - Sandawana (Zimbabwe) + - Colombian (Muzo) + - Zambian + - Ural (Russia) + rows: + - ["Diagnostic inclusion", "Tremolite needles", "Parisite + halite in 3-phase", "Biotite mica", "Phlogopite mica"] + - ["Fe content", "Very low", "Very low", "Moderate–high", "Low"] + - ["Cr content", "Very high", "High", "Moderate", "Moderate"] + - ["LWUV fluorescence", "Very strong red", "Strong red", "Moderate red", "Moderate red"] + - ["Typical size", "Very small (<0.5 ct)", "Wide range", "Small to medium", "Small to medium"] + - ["Li content", ">200 ppmw", "<200 ppmw", ">200 ppmw", ">200 ppmw"] + + - title: Marange Diamond (Zimbabwe) + content: | + The Marange alluvial diamond field: + subsections: + - title: Discovery and Controversy + content: | + - Marange (Manicaland Province, eastern Zimbabwe): One of the largest alluvial + diamond deposits discovered in the 20th century, found in 2006 + - Stones distributed through fluvial and aeolian gravels overlying kimberlite + - Became controversial due to alleged human rights abuses; Kimberley Process + imposed scrutiny; exports were blocked then reinstated + + - title: Gemmological Profile + content: | + - Marange diamonds span from heavily included, graphite-laden brownish-grey + stones (most common) to rare near-colourless and fancy yellow material + - Many stones commercially treated (HPHT or fracture-filling) to improve appearance + - Standard gemmological identification methods apply; no diagnostic inclusion + suite unique to Marange has been documented in peer-reviewed gemmological + literature retrieved from the research database + + - title: Murehwa Chrysoberyl — Citation Note + callout: + type: warning + title: CITATION NEEDED — Murehwa Chrysoberyl + text: | + The Murehwa district (Mashonaland East Province) is noted as hosting LCT pegmatites + carrying chrysoberyl, occasionally of alexandrite quality. However, no peer-reviewed + gemmological characterisation paper for Murehwa chrysoberyl was retrieved from + the research database — this locality is [UNVERIFIED] per VERIFIED.md (D-05). + + It is noted here for completeness; specific gemmological diagnostics cannot be + stated without a sourced paper. Colour change is reportedly modest compared + to Russian or Brazilian alexandrite. + +sources: + - doi: "10.5741/gems.33.2.80" + citation: "Zwaan, Kanis & Petsch (1997) Emerald from Zimbabwe. Gems & Gemology." + - doi: "10.15506/jog.1998.26.3.174" + citation: "Zwaan & Burke (1998) Raman microspectroscopy of Sandawana emerald inclusions. Journal of Gemmology." + - doi: "10.1016/j.crte.2003.10.015" + citation: "Stable-isotope tracing of Sandawana emerald fluid mixing genesis (2004). Comptes Rendus Géoscience." + - doi: "10.3390/min9090561" + citation: "Karampelas et al. (2019) Emeralds from the Most Important Occurrences. Minerals." diff --git a/docs/learn/phenomena/alexandrite-effect.yaml b/docs/learn/phenomena/alexandrite-effect.yaml new file mode 100644 index 0000000..644055d --- /dev/null +++ b/docs/learn/phenomena/alexandrite-effect.yaml @@ -0,0 +1,166 @@ +title: Alexandrite Effect — Physical Mechanism +description: Deep dive into the alexandrite effect — Cr³⁺ in trigonal crystal field, the dual transmission window, photopic peak balance, named species including garnets, sapphire, and synthetic spinel, and how to test colour change under standardised illuminants. +order: 16 +category: phenomena +difficulty: advanced +icon: sun-moon +related: + - phenomena/colour-change + - phenomena/tenebrescence + - species/chrysoberyl + - species/garnet +tags: + - phenomena/alexandrite-effect + - alexandrite + - chromium + - colour-change + - crystal-field + +sections: + - title: Definition + content: | + The alexandrite effect is the reversible, repeatable shift in apparent body colour of a + gemstone when the illuminant changes from daylight (approximately 6500 K, blue-rich) to + incandescent light (approximately 2700–3200 K, red-rich). + + It is caused by a dual transmission window in the gem's absorption spectrum: the stone + transmits both red (~650–700 nm) and blue-green (~450–510 nm) wavelengths simultaneously. + Which colour the eye perceives as dominant depends on the spectral power distribution of + the illuminant in those two regions. + + This page provides the physical mechanism underpinning colour change as described in the + overview page. For grading, quality factors, and broader colour-change gem survey, see + the companion page on Colour Change. + + - title: Mechanism + content: | + The crystal field physics of Cr³⁺ in chrysoberyl: + subsections: + - title: Chromophore and Crystal Field + content: | + In alexandrite (the colour-change variety of chrysoberyl, BeAl₂O₄), the colour-active + ion is Cr³⁺ substituting for Al³⁺ in a distorted octahedral site. The octahedral + crystal field splits the Cr³⁺ d-orbital energy levels, creating two broad absorption + bands: + + - One centred around 550–580 nm (yellow-green) + - One in the UV/violet (~400 nm) + + These two bands leave two transmission windows: + - Red window (~650–700 nm) + - Blue-green window (~450–510 nm) + + The stone transmits both simultaneously — this is the structural prerequisite for the + alexandrite effect. + + - title: The Photopic Peak and Illuminant Dependence + content: | + Human daylight (photopic) vision is most sensitive near 555 nm. The Cr³⁺ absorption + at ~560 nm sits exactly at the photopic peak, suppressing the eye's most sensitive + wavelength range. What remains to dominate the perceived colour depends entirely on + illuminant composition: + + - **Daylight (D65, ~6500 K)** — strong blue-green component in the illuminant + preferentially excites the blue-green transmission window → stone appears green to teal + - **Incandescent (~2700 K, tungsten)** — weak blue, strong red in the illuminant + preferentially excites the red transmission window → stone appears red to purplish-red + + Qiu & Guo (2021) confirmed this mechanism in pyrope-spessartine colour-change garnets: + "As they exhibit the same capacity to transmit light, the colour of the gem is + determined by the external light source." + + - title: Crystal Field Context + content: | + Why does Cr³⁺ produce red in ruby, green in emerald, and teal-green/red in alexandrite? + + The octahedral crystal field strength (Δo) differs by host mineral: + - **Corundum (ruby)**: Strong octahedral field → Cr³⁺ absorbs at shorter wavelengths + → absorption band shifts toward blue-green → red light passes → red colour + - **Beryl (emerald)**: Weaker field → absorption band shifts toward longer wavelengths + → red light partially absorbed → green light passes + - **Chrysoberyl (alexandrite)**: Intermediate field → two absorption bands straddle + the visible spectrum, leaving both red and blue-green to pass → alexandrite effect + + - title: Named Species + table: + caption: Gem species showing the alexandrite effect. [PARTIALLY_SUPPORTED] for diaspore — no DOI-verified primary spectroscopic paper on diaspore colour-change mechanism was retrieved in the source research session; the effect is well-known but the ion assignment relies on standard references [PARTIALLY_SUPPORTED]. + headers: + - Species / Variety + - Active Ion(s) + - Daylight Colour + - Incandescent Colour + - Quality / Notes + rows: + - ["Alexandrite (chrysoberyl var.)", "Cr³⁺", "Green to teal", "Red to purplish-red", "Strongest and most complete change known; benchmark for all colour-change gems. Schmetzer & Malsy (2011) [VERIFIED]"] + - ["Colour-change garnet (pyrope-spessartine)", "Cr³⁺ + V³⁺", "Blue-green to teal", "Purple to red", "Very strong; best specimens rival alexandrite in completeness. Qiu & Guo (2021) [VERIFIED]"] + - ["Colour-change sapphire (corundum)", "V³⁺ (± Cr³⁺)", "Blue to violet", "Purple to red", "Variable; often greyish intermediate colour; locality affects quality"] + - ["Colour-change diaspore ('zultanite', 'csarite')", "V³⁺ + Cr³⁺ (proposed)", "Kiwi green", "Pinkish champagne", "Subtle but characteristic change; spectroscopic assignment [PARTIALLY_SUPPORTED] — no dedicated DOI-verified primary paper retrieved"] + - ["Colour-change synthetic spinel (Co-doped)", "Co²⁺", "Blue-green", "Red-pink", "Common in older synthetic 'alexandrite' simulants; chalky blue-white SW fluorescence distinguishes from alexandrite"] + - ["Colour-change fluorite (some)", "[CITATION NEEDED]", "Various", "Various", "Weak; mechanism not confirmed; not diagnostically significant"] + + - title: How to Test the Alexandrite Effect + content: | + Standardised testing conditions for colour-change assessment: + subsections: + - title: Light Source Requirements + content: | + - **Daylight equivalent**: D65 fluorescent lamp or north-facing window light (overcast sky). + Avoid mixed LED lighting — LED spectra vary widely and may not reproduce the effect + consistently. + - **Incandescent**: Standard tungsten bulb (~2700 K). Not LED or halogen at high colour + temperature; these do not have sufficient red component to show the full change. + + Observe the stone under each source in turn and note the dominant hue in each condition. + + - title: Grading the Change + content: | + - **Complete change** (100%): Pure green/teal in daylight; pure red in incandescent; no + intermediate or residual colour of the other type + - **Strong** (75–99%): Clearly different hues with minor residual component + - **Moderate** (50–74%): Distinct but less dramatic shift + - **Weak** (<50%): Slight shift only; marginally perceptible + + Laboratory reports use CIE colorimetry under D65 vs Standard Illuminant A to quantify + change objectively. + + - title: Species Identification After Colour Change Confirmation + content: | + Confirming the alexandrite effect does not identify the species. Use RI, SG, and + spectroscopic data to determine the mineral: + + - Green → strong red; RI 1.746–1.755; SG ~3.73 → alexandrite (chrysoberyl) + - Blue-green → strong red; RI 1.740–1.760; SG ~3.8–4.0 → colour-change garnet + - Blue-grey → weak purple; RI 1.760–1.770; SG ~4.0 → colour-change sapphire + - Green → pinkish champagne; RI 1.700–1.750; SG ~3.3–3.4 → diaspore + + - title: Synthetic Alexandrite Diagnostics + content: | + Separating natural alexandrite from synthetic varieties: + subsections: + - title: Growth Features + content: | + Natural alexandrite shows planar growth zones (fingerprints, two-phase fluid inclusions, + chrysotile fibres) typical of metamorphic or pegmatitic origin. Schmetzer, Bernhardt & + Hainschwang (2013) documented titanium-bearing synthetic alexandrite grown by flux and + hydrothermal methods, noting curved growth planes and specific UV-Vis absorption + differences (Ti⁴⁺ bands) absent in natural material. + + - title: Fluorescence Contrast + content: | + Natural alexandrite: moderate red LWUV fluorescence (Cr³⁺, low-quenching chrysoberyl). + Synthetic colour-change spinel simulant: chalky blue-white SW fluorescence (Co²⁺ or + Ti⁴⁺) — completely different response, immediately diagnostic. + + Synthetic alexandrite (Cr-doped) shows similar LWUV red to natural but lacks natural + inclusion types; growth features are definitive under magnification. + + - title: Sources + items: + - name: Qiu & Guo (2021) + description: "Explaining Colour Change in Pyrope-Spessartine Garnets. Minerals 11(8), 865. DOI: 10.3390/min11080865. [VERIFIED] — Quantitative UV-Vis spectroscopic confirmation of dual transmission window mechanism; abstract explicitly describes the two transmittance zones and illuminant-dependence." + - name: Schmetzer & Malsy (2011) + description: "Alexandrite and colour-change chrysoberyl from the Lake Manyara alexandrite-emerald deposit in northern Tanzania. The Journal of Gemmology 32(5), 179–209. DOI: 10.15506/jog.2011.32.5.179. [VERIFIED] — Detailed optical characterisation of alexandrite; Cr³⁺ as chromophore confirmed." + - name: Schmetzer, Bernhardt & Hainschwang (2013) + description: "Titanium-bearing synthetic alexandrite and chrysoberyl. The Journal of Gemmology 33(5), 137–148. DOI: 10.15506/jog.2013.33.5.137. [VERIFIED] — Synthetic alexandrite diagnostics; Ti⁴⁺ absorption differences." + - name: Read (2008) + description: "Gemmology (3rd ed.). Butterworth-Heinemann/Routledge. DOI: 10.4324/9780080507224. [APPROXIMATE] — Crystal field context and named species survey." diff --git a/docs/learn/phenomena/fire-dispersion.yaml b/docs/learn/phenomena/fire-dispersion.yaml new file mode 100644 index 0000000..d7b6d34 --- /dev/null +++ b/docs/learn/phenomena/fire-dispersion.yaml @@ -0,0 +1,150 @@ +title: Fire and Dispersion +description: Fire in faceted gemstones — dispersion as differential refraction by wavelength, the B–G interval, named dispersion values, relationship to facet design, and distinction from diffraction-based spectral effects. +order: 13 +category: phenomena +difficulty: intermediate +icon: flame +related: + - phenomena/overview + - phenomena/play-of-colour + - phenomena/iridescence +tags: + - phenomena/fire + - phenomena/dispersion + - refraction + - diamond-simulants + - facet-design + +sections: + - title: Definition + content: | + Fire is the splitting of white light into its spectral colours (red, orange, yellow, green, + blue, violet) visible as coloured flashes in a faceted gemstone. It arises from dispersion — + the variation of refractive index with wavelength — and is enhanced by facet geometry and + viewing conditions. + + Fire is not the same as play-of-colour (opal) or labradorescence: those spectral effects + arise from diffraction or thin-film interference. Fire results from differential refraction + at every facet interface. + + - title: Mechanism + content: | + The physics of dispersion and fire: + subsections: + - title: Dispersion Defined + content: | + Refractive index (RI) varies with wavelength: shorter wavelengths (violet, blue) are + refracted more strongly at any interface than longer wavelengths (red, orange). This + wavelength-dependence of RI is dispersion. When white light enters a gem, each colour + component is refracted by a slightly different angle; on exit, the colours emerge at + different positions, producing visible spectral separation — fire. + + - title: Why Dispersion is Not Diffraction + content: | + - **Diffraction** involves wave bending around apertures or at periodic structures + (silica sphere arrays in opal, nacre platelet stacks in pearl) — structural colour. + - **Dispersion** involves differential refraction at an interface between two media + of differing refractive index — a bulk optical property of the material. + + Both produce spectral colours but at entirely different physical length scales and by + different mechanisms. In a faceted gem, fire is produced at each facet face; in opal, + colour arises from the photonic crystal structure of ~200 nm silica spheres. + + - title: The B–G Interval + content: | + Gemmological dispersion is conventionally measured as the difference in refractive + index between Fraunhofer lines B (686.7 nm, deep red) and G (430.8 nm, violet): + + **Dispersion = n_G − n_B** + + A larger B–G value means greater potential for fire. Values are material constants, + independent of cut geometry. + + - title: Named Dispersion Values + table: + caption: "B–G dispersion values for selected gem species and simulants. Source: Read (2008) [APPROXIMATE] — no single DOI-verified comprehensive dispersion table was located; diamond, zircon, and moissanite values confirmed across multiple textbook sources. CZ = 0.060 (Read 7th ed. preferred value); do NOT use 0.065 from uncited trade sources." + headers: + - Species + - B–G Dispersion + - Notes + rows: + - ["Strontium titanate (simulant)", "0.190", "Extremely high; immediately obvious excessive fire"] + - ["Rutile (TiO₂, historical simulant)", "0.280", "Far exceeds diamond; strong birefringence also diagnostic"] + - ["Synthetic moissanite", "0.104", "More than twice diamond; combined with birefringence is diagnostic"] + - ["Cubic zirconia (CZ)", "0.060", "Higher than diamond; conspicuous fire. Note: 0.060 is the Read 7th-edition canonical value; the value 0.065 appears in some trade sources without primary citation and is not used here"] + - ["GGG (gadolinium gallium garnet)", "0.045", "Higher than diamond; obsolete simulant"] + - ["Diamond", "0.044", "High for natural gems; the benchmark reference value"] + - ["Demantoid (andradite garnet)", "0.057", "Higher than diamond; contributes to demantoid's famous fire"] + - ["Sphene (titanite)", "0.051", "Very high; softness limits durability for jewellery"] + - ["YAG (yttrium aluminium garnet)", "0.028", "Moderate; obsolete simulant"] + - ["Almandine garnet", "0.027", "Moderate; low fire contributes to darker appearance"] + - ["Zircon (high type)", "0.039", "Moderate fire; good dispersion for affordable stone; also birefringent"] + - ["Sapphire (corundum)", "0.018", "Low; fire not a notable feature of sapphire"] + - ["Topaz", "0.014", "Low; relatively little fire"] + - ["Quartz", "0.013", "Low"] + - ["Fluorite", "0.007", "Very low; glass-like appearance"] + + - title: Facet Design and Fire + content: | + Fire is not purely a material property — cut geometry strongly determines how much + dispersion is visible: + subsections: + - title: Cut Geometry + content: | + A brilliant cut allows white light to enter through the table, undergo total internal + reflection at the pavilion facets, and exit through the crown facets. Each reflection + and refraction event disperses the light further. The crown height, facet angles, and + number of facets all influence how the dispersed colours emerge to the viewer. + + Very shallow or very deep pavilion angles reduce total internal reflection and therefore + reduce both brilliance and fire. + + - title: Trade-off with Brilliance + content: | + High dispersion often correlates with high RI (both increase as electron density + increases). However, brilliance (white light return) and fire compete in cut design: + + - A broad table suppresses fire (less crown facet area to produce coloured flashes) + - More and smaller crown facets generate more fire at the cost of some brilliance + - The classic round brilliant optimises both for diamond + + - title: Distinguishing Fire from Other Spectral Effects + table: + caption: Fire versus diffraction-based and interference-based spectral colour effects + headers: + - Effect + - Mechanism + - Visual Character + - Host Material + rows: + - ["Fire (dispersion)", "Differential refraction at gem facets", "Coloured flashes that change with viewing angle; seen in faceted gems", "Faceted stones"] + - ["Play-of-colour (opal)", "Diffraction from silica sphere array (~200 nm)", "Spectral colour patches shifting with viewing angle; cabochon or rough", "Precious opal"] + - ["Labradorescence", "Thin-film interference in Bøggild intergrowth", "Directional broad colour zones in feldspar; not rapid flashes", "Labradorite feldspar"] + - ["Orient (pearl)", "Thin-film diffraction/interference in nacre platelets", "Soft iridescent surface bloom; not rapid flashes", "Nacre-covered pearls"] + - ["Iridescence (general)", "Thin-film interference or diffraction", "Broad spectral sheen associated with surface or near-surface structure", "Fire agate, ammolite, surface films"] + + - title: Diagnostic Relevance + content: | + Using dispersion in gem identification: + subsections: + - title: High Fire as Diagnostic + content: | + Fire conspicuously greater than diamond narrows identification to a short list. + Combine dispersion observation with RI, SG, and optic character: + + - Excessive fire + birefringence (doubling of facet edges) = moissanite + - Excessive fire + high SG, no birefringence = CZ or GGG (historical) + - Extreme fire + very high birefringence = rutile or synthetic rutile (historical) + + - title: Low Fire as Diagnostic + content: | + A colourless stone with very little fire but high RI may be zircon (also birefringent + under magnification) or a heavy-element glass. Sapphire has low dispersion (0.018) so + shows little fire despite its relatively high RI. + + - title: Sources + items: + - name: Read (2008) + description: "Gemmology (3rd ed.). Butterworth-Heinemann/Routledge. DOI: 10.4324/9780080507224. [APPROXIMATE — chapter confirmed; page references not independently verified] — Primary source for dispersion mechanism and B–G values. No single DOI-verified comprehensive dispersion table paper was located in the source research session; values are textbook-consensus and should be verified against a primary spectrophotometric source before formal examination use. [Confidence C for the full dispersion table]" + - name: Nassau (2001) + description: "The Physics and Chemistry of Color (2nd ed.). Wiley-Interscience. No DOI retrieved. [UNVERIFIED] — Conceptual support for dispersion mechanism." diff --git a/docs/learn/phenomena/fluorescence.yaml b/docs/learn/phenomena/fluorescence.yaml new file mode 100644 index 0000000..c9d134a --- /dev/null +++ b/docs/learn/phenomena/fluorescence.yaml @@ -0,0 +1,181 @@ +title: Fluorescence and Phosphorescence +description: Fluorescence and phosphorescence in gemstones — Stokes shift mechanism, LWUV vs SWUV regimes, species reaction table, phosphorescence afterglow, and diagnostic applications for natural vs synthetic identification. +order: 12 +category: phenomena +difficulty: intermediate +icon: zap +related: + - phenomena/overview + - phenomena/tenebrescence + - equipment/uv-lamp +tags: + - phenomena/fluorescence + - phenomena/phosphorescence + - uv-luminescence + - diamond-detection + - synthetics + - chromophores + +sections: + - title: Definition + content: | + Fluorescence is the immediate emission of photons of longer wavelength (lower energy) than + the exciting radiation when a gemstone absorbs ultraviolet, visible, or X-ray radiation. + Emission ceases essentially instantaneously (lifetime < 10⁻⁸ s) when the excitation source + is removed. + + Phosphorescence is the delayed emission of light persisting measurably after the excitation + source is removed; it results from metastable electronic states in which excited electrons + are temporarily trapped before returning to ground state, producing an afterglow lasting + from milliseconds to minutes. + + Both are distinct from the gem-testing instrument context (UV lamp selection, geometry, + box design) covered separately under equipment. + + - title: Mechanism — Stokes Shift + content: | + The physical basis of fluorescence: + subsections: + - title: Energy and Emission + content: | + When a gem absorbs a UV photon, electrons are promoted to a higher energy level. Before + emitting a photon of their own, they lose some energy to lattice vibrations (phonons). + The emitted photon therefore has lower energy — longer wavelength — than the absorbed + photon. This energy difference is the Stokes shift. + + Consequence: emitted light is always at longer wavelength (redder) than the exciting + radiation. A UV source (365 nm or 254 nm) produces visible-wavelength emission. + + - title: Activators and Chromophores + content: | + - **Cr³⁺** — intense red emission ~692–694 nm (ruby R-lines); low-iron corundum + - **N3 centre** (three N atoms + vacancy in diamond) — absorbs at ~415 nm; emits blue (~440–460 nm) under LWUV + - **Mn²⁺** — broad orange-red emission in calcite, scheelite, some fluorites + - **UO₂²⁺ (uranyl ion)** — sharp green bands ~490–570 nm in hyalite opal + - **Ti⁴⁺** — blue emission in Verneuil synthetic spinel (chalky character) + + - title: LWUV vs SWUV Regimes + content: | + Two distinct excitation wavelengths are used in gemmological practice: + subsections: + - title: Longwave UV (LWUV, 365 nm) + content: | + Corresponds to the standard UV lamp emission at 365 nm. Penetrates more deeply into + the stone. Most natural gems show stronger or more characteristic fluorescence under + LWUV than SWUV. The LWUV response is often the primary routine triage tool. + + - title: Shortwave UV (SWUV, 254 nm) + content: | + Higher-energy excitation (254 nm, germicidal lamp). Activates different electronic + transitions; essential for synthetic spinel detection and many diagnostic contrasts. + SWUV reactions often separate natural from synthetic where LWUV cannot. + + The two lamps test different electronic levels and commonly produce different fluorescence + colours and intensities from the same stone — together they provide a two-point diagnostic. + + - title: Fluorescence Reactions by Species + table: + caption: LWUV and SWUV fluorescence responses for key gem species + headers: + - Species / Variety + - LWUV (365 nm) + - SWUV (254 nm) + - Activator / Defect + - Notes + rows: + - ["Ruby — Mogok (Burma)", "Strong red", "Moderate to strong red", "Cr³⁺", "Low Fe content; minimal quenching; strong LW fluorescence is characteristic of Mogok material (Keller 1983)"] + - ["Ruby — Thai/Cambodian", "Weak to inert", "Inert", "Cr³⁺ quenched by Fe²⁺", "High Fe (>1000 ppm) suppresses Cr³⁺ fluorescence; diagnostic contrast with Mogok"] + - ["Flux synthetic ruby (Ramaura, Kashan, Chatham)", "Strong to very strong red", "Strong red", "Cr³⁺ (no Fe quenching in flux growth)", "Often stronger than natural Mogok due to very low Fe; combine with inclusion observation to confirm synthetic"] + - ["Diamond — type Ia (N3)", "Blue to blue-white (strong to moderate)", "Weak to moderate; may show yellow SW", "N3 centre (415 nm)", "Most natural colourless/near-colourless diamonds; LWUV blue is the most common response"] + - ["Diamond — type IIa", "Usually inert", "Usually inert", "No N3; no aggregated N", "Some type IIa show weak blue LWUV; absence of fluorescence combined with high transparency is characteristic"] + - ["Diamond — CVD synthetic", "Inert to weak orange/yellow LW", "Orange, red, or persistent orange-red SW", "NV centres, Si-V, interstitial defects", "Persistent SW phosphorescence is an important diagnostic indicator for CVD — see phosphorescence section below; note: primary peer-reviewed paper for this specific response not yet confirmed [CITATION NEEDED]"] + - ["Diamond — HPHT synthetic", "Yellow-green to inert LW", "Yellow-green SW; may show persistent blue-green phosphorescence", "N-V centre, H3 centre", "Zhu et al. (2024) documented an HPHT diamond with engineered N3-derived blue LW fluorescence mimicking type Ia; requires FTIR confirmation"] + - ["Synthetic spinel (Verneuil)", "Chalky blue-white (intense)", "Chalky green-blue (intense)", "Ti⁴⁺ or related activator", "Highly diagnostic; chalky SW response is the single most reliable indicator of Verneuil synthetic spinel"] + - ["Natural spinel (Cr-rich red)", "Orange-red", "Orange", "Cr³⁺", "Moderate to strong; far less intense than the chalky SW response of Verneuil spinel"] + - ["Natural emerald (Colombian)", "Inert to very weak red LW", "Inert", "Cr³⁺ quenched by Fe", "Colombian emerald characteristically very weak or inert"] + - ["Flux synthetic emerald (Chatham, Gilson)", "Strong red LW", "Strong red SW", "Cr³⁺ (iron-free growth medium)", "Among the most reliable rapid tests; natural Colombian inert vs flux synthetic strong red"] + - ["Hydrothermal synthetic emerald", "Weak to moderate red LW", "Moderate red SW", "Cr³⁺; slightly more Fe than flux", "Less strongly fluorescing than flux synthetics; still diagnostic vs Colombian natural"] + - ["Natural topaz (orange 'imperial')", "Orange-yellow LW", "Orange-yellow SW", "Cr³⁺ or charge-transfer", "Variable; orange-yellow LW is typical of untreated imperial topaz [PARTIALLY_SUPPORTED]"] + - ["Kunzite (spodumene)", "Strong orange to orange-pink LW", "Orange SW", "Mn²⁺ or related activator", "Strong orange LW is diagnostic for kunzite [PARTIALLY_SUPPORTED]"] + - ["Hyalite opal", "Intense green LW", "Intense green SW", "UO₂²⁺ (uranyl ion)", "Uranium-containing variety; bright green is characteristic and diagnostic"] + - ["Scheelite (CaWO₄)", "Bright blue-white LW", "Intense blue-white SW", "W⁶⁺ / Mo⁶⁺", "SW fluorescence is diagnostic for scheelite vs visually similar stones [PARTIALLY_SUPPORTED]"] + - ["Benitoite (BaTiSi₃O₉)", "Intense blue LW", "Intense blue SW", "Ti⁴⁺", "Extremely intense blue SW; one of the brightest naturally occurring SW fluorescences known [PARTIALLY_SUPPORTED]"] + - ["Calcite", "Red to pink LW", "Red to pink SW", "Mn²⁺", "Useful for detecting calcite in composite stones; many limestone-derived materials fluoresce"] + - ["Pearl (Akoya, cultured)", "Chalky white to blue-white LW", "Variable", "Organic matrix + Mn²⁺", "Weak fluorescence common; treated dark Akoya (gamma-irradiated) may show red LW — treatment indicator"] + + - title: Phosphorescence + content: | + Afterglow following removal of the excitation source: + subsections: + - title: Physical Distinction from Fluorescence + content: | + In fluorescence, the transition from excited to ground state is spin-allowed; emission + is near-instantaneous (10⁻⁸ to 10⁻⁹ s). In phosphorescence, excited electrons occupy + a metastable triplet or trap state from which the return to ground state is spin-forbidden; + emission is delayed from milliseconds to many minutes. + + - title: Detection Method + content: | + Examine in complete darkness immediately after turning off the SWUV source. Wait at + least 30 seconds; CVD diamond orange-red afterglow may persist 30–120 seconds. A + darkened room and phone camera can photograph persistent luminescence. + + - title: Phosphorescence by Species + table: + headers: + - Species + - Phosphorescence Colour + - Approximate Duration + - Significance + rows: + - ["Hackmanite (sodalite var.)", "Yellow-orange", "Several seconds", "Normal feature of tenebrescence cycle; Kondo & Beaton 2009 [VERIFIED]"] + - ["HPHT synthetic diamond", "Blue-green (H3 or N-related)", "Several seconds", "Diagnostic for HPHT type; natural equivalents rare; Zhu et al. 2024 [VERIFIED]"] + - ["CVD synthetic diamond", "Orange to red", "30 s to several minutes", "Highly diagnostic; almost never seen in natural diamonds — note: primary peer-reviewed paper not yet confirmed [CITATION NEEDED]"] + - ["Type IIb natural diamond (boron-bearing)", "Blue", "Several seconds", "Very rare; boron acceptor trap; natural examples confirmed"] + - ["ZnS-imitation 'gems'", "Bright green", "Minutes to hours", "Clear indicator of novelty/fake material; ZnS phosphor pigment"] + + - title: Diagnostic Relevance + content: | + Fluorescence in identification practice: + subsections: + - title: Routine Triage + content: | + A dual-lamp UV box (LWUV + SWUV) is among the first instruments used in gem + identification. Fluorescence alone does not identify a stone unambiguously but provides + critical sorting information that narrows the field quickly. + + - title: Natural vs Synthetic Emerald + content: | + The contrast between natural Colombian emerald (weak/inert) and flux synthetic emerald + (strong red LW and SW) is one of the most reliable rapid tests in gemmology. Note that + emeralds from other origins (Zambia, Brazil) may also show weak fluorescence, but the + contrast with flux synthetics remains strong. + + - title: Diamond Type and Synthetic Detection + content: | + Most natural diamonds are type Ia and show blue LWUV. Most HPHT synthetics show + yellow-green (H3 centre). CVD synthetics frequently show phosphorescence under SWUV. + However, Zhu et al. (2024) demonstrated that some HPHT diamonds can be engineered + with N3-derived blue LWUV fluorescence that mimics natural type Ia — requiring + FTIR confirmation for definitive classification. + + - title: Iron Quenching Effect + content: | + High iron content suppresses Cr³⁺ fluorescence. Thai/Cambodian rubies (Fe > 1000 ppm) + appear inert under LWUV, while low-iron Mogok rubies fluoresce strongly red. + This contrast is a primary origin indicator (Keller 1983). + + - title: Sources + items: + - name: Keller (1983) + description: "The Rubies of Burma: A Review of the Mogok Stone Tract. Gems & Gemology 19(4), 209–219. DOI: 10.5741/gems.19.4.209. [VERIFIED] — Documents strong red LWUV fluorescence as characteristic of Mogok ruby." + - name: Zhu et al. (2024) + description: "A Near-Colourless HPHT-grown Diamond with Natural-appearing Blue Fluorescence from N3 Centres. The Journal of Gemmology 39(1), 24–26. DOI: 10.15506/jog.2024.39.1.24. [VERIFIED]" + - name: Zhu et al. (2022) + description: "Melee-Sized Colourless HPHT-Grown Synthetic Diamond with Red Fluorescence. The Journal of Gemmology 38(2), 128–129. DOI: 10.15506/jog.2022.38.2.128. [VERIFIED]" + - name: Kondo & Beaton (2009) + description: "Hackmanite/Sodalite from Myanmar and Afghanistan. Gems & Gemology 45(1), 38–43. DOI: 10.5741/gems.45.1.38. [VERIFIED] — Hackmanite yellow-orange phosphorescence." + - name: Radomskaya et al. (2021) + description: "Sulfur-Bearing Sodalite, Hackmanite, in Alkaline Pegmatites of the Inagli Massif. Geology of Ore Deposits 63(7). DOI: 10.1134/s1075701521070060. [VERIFIED] — Hackmanite luminescence and crystal chemistry." + - name: Read (2008) + description: "Gemmology (3rd ed.). Butterworth-Heinemann/Routledge. DOI: 10.4324/9780080507224. [APPROXIMATE] — Fluorescence reactions by species; general mechanism." diff --git a/docs/learn/phenomena/orient.yaml b/docs/learn/phenomena/orient.yaml new file mode 100644 index 0000000..5c7bbde --- /dev/null +++ b/docs/learn/phenomena/orient.yaml @@ -0,0 +1,143 @@ +title: Pearl Orient +description: Pearl orient — the soft iridescent surface bloom of fine nacre, arising from thin-film diffraction and interference at aragonite tablet layers, distinguished from body colour, lustre, and fluorescence. +order: 14 +category: phenomena +difficulty: intermediate +icon: gem +related: + - phenomena/overview + - phenomena/iridescence + - phenomena/play-of-colour +tags: + - phenomena/orient + - pearl + - nacre + - aragonite + - cultured-pearl + - pearl-grading + +sections: + - title: Definition + content: | + Pearl orient is the soft, shimmering, multi-tonal iridescence visible at the surface of + high-quality nacre-covered pearls. It arises from diffraction and interference of light at + the layered aragonite platelet structure of nacre. + + Orient is entirely distinct from: + - **Body colour** — the dominant saturation and hue of the pearl (white, cream, golden, black) + - **Lustre** — the intensity and quality of the surface reflection + - **Fluorescence** — emission under UV excitation + + A pearl may have high lustre but weak orient (thin nacre), or a deep body colour with strong + orient. All four qualities are assessed independently in professional pearl grading. + + - title: Mechanism + content: | + Physical cause of orient in nacre: + subsections: + - title: Nacre Structure + content: | + Pearl nacre consists of thin hexagonal aragonite (CaCO₃) tablets approximately + 0.4–0.6 µm thick (400–600 nm) stacked in columns and separated by thin organic + matrix sheets. Ozaki et al. (2017) calculated the reflection spectrum of Akoya pearl + nacre using actual layer thickness profiles and confirmed that the periodicity of the + nacre layers produces structural colour effects via thin-film interference. + + - title: Diffraction and Interference + content: | + When white light strikes the nacre surface it is partially reflected at each layer + interface (aragonite/organic boundary). Because layer thickness (~0.5 µm) is + comparable to the wavelength of visible light, constructive interference selectively + reflects certain wavelengths at each viewing angle. + + As the viewing angle changes, different wavelengths constructively interfere, producing + the soft spectral iridescence visible as orient. The regular stacking also acts as a + diffraction grating for oblique rays, contributing additional angular colour separation. + + - title: Distinction from Lustre + content: | + Lustre is the quality and intensity of surface reflection — related to the smoothness + and translucency of the outermost nacre layers. Orient is the iridescent hue-shifting + effect superimposed on lustre. Both depend on nacre quality, but lustre responds to + surface smoothness while orient responds to layer periodicity and thickness uniformity. + + - title: Named Pearl Types and Orient Character + table: + caption: Orient characteristics across major pearl types. [PARTIALLY_SUPPORTED] — no single DOI-verified paper comparing orient across all types was retrieved; characteristics are consensus from standard gemmological references (Read 2008) + headers: + - Pearl Type + - Mollusc / Species + - Nacre Tablet Thickness + - Orient Character + rows: + - ["Akoya", "Pinctada fucata", "~0.4–0.5 µm; relatively uniform", "Delicate rose to green overtone; characteristic 'rosé' overtone prized in Japanese Akoya; quantified by Ozaki et al. 2017 [VERIFIED]"] + - ["South Sea", "Pinctada maxima", "Thicker tablets ~0.6–0.8 µm; silver or golden body", "Soft, broad orient; less intense iridescence than Akoya due to thicker layers; very high lustre"] + - ["Tahitian", "Pinctada margaritifera", "Intermediate thickness; dark body", "Peacock orient — green to reddish iridescence over dark body; the characteristic Tahitian overtone"] + - ["Natural seawater", "Various Pinctada spp.", "Variable; often thicker nacre than cultured (years of growth)", "Often strong orient; nacre thickness benefits from longer time in the water"] + - ["Freshwater cultured", "Hyriopsis spp.", "Variable; all-nacre (no shell-bead nucleus)", "Improving quality; solid nacre throughout; orient variable depending on processing"] + + - title: Cultured vs Natural Pearl Orient + content: | + Comparing orient between cultured and natural pearls: + subsections: + - title: Nacre Thickness + content: | + Natural seawater pearls typically have much thicker nacre than bead-nucleated cultured + pearls because the oyster deposits nacre over many years. Thicker nacre generally + produces deeper orient and the nacre layers have more time to develop uniform thickness. + + Thin-nacre cultured pearls (sometimes called "soufflé" if very thin) may have high + lustre but weak or absent orient. Nacre thickness in bead-nucleated cultured pearls is + visible by X-ray: the bead core appears distinct from the nacre layer. + + - title: Freshwater All-Nacre Structure + content: | + Freshwater cultured pearls (mantle-tissue nucleated, no shell bead) are composed + entirely of nacre. This structure — similar to natural pearls in composition — can + produce genuine orient, though layer uniformity affects quality. The finest Chinese + freshwater pearls increasingly approach Akoya orient quality. + + - title: Distinguishing Orient from Related Effects + table: + caption: Orient versus other visual effects in pearl and imitation materials + headers: + - Effect + - Cause + - Pearl-specific? + - Test + rows: + - ["Orient", "Thin-film diffraction/interference in nacre aragonite layers", "Yes — defining feature of fine nacre", "Visible under ordinary white light; soft multi-tonal iridescence"] + - ["Body colour", "Organic pigment (porphyrins) + optical depth effects", "Yes", "Colour visible in direct light; does not shift spectrally with angle"] + - ["Lustre", "Surface reflectance quality of outermost nacre", "Yes", "Sharpness of reflected image; independent of orient"] + - ["Fluorescence", "UV-induced emission (organic matrix + Mn²⁺)", "Yes", "Visible only under UV lamp; inert under ordinary light"] + - ["Coating iridescence (imitation)", "TiO₂ or fish-scale essence d'orient on glass/plastic bead", "Imitation only", "Tooth test (gritty = genuine nacre); X-ray shows no nacre layers; SG ~2.7 for genuine nacre vs ~2.4 for glass"] + + - title: Diagnostic Relevance + content: | + Orient in pearl identification and grading: + subsections: + - title: Quality Factor + content: | + Strong orient increases pearl value. It is assessed as one of several quality factors + alongside lustre, surface, shape, colour, and size. The characteristic Tahitian peacock + orient (green + reddish iridescence on dark body) is a premium quality indicator. + + - title: Nacre Thickness Indicator + content: | + Absence of orient in a cultured pearl may indicate very thin nacre or a coated + imitation. Nacre thickness can be checked by observing the drill hole under magnification + (concentric layers visible) or by X-ray fluorescence. + + - title: Imitation Detection + content: | + Imitation pearls coated with fish-scale essence d'orient (guanine platelets) or TiO₂ + can simulate orient superficially. However, they lack the nacre microstructure; the + tooth test (genuine nacre feels gritty; imitation feels smooth), X-ray, and microscopic + examination of the drill hole distinguish genuine nacre from coating. + + - title: Sources + items: + - name: Ozaki et al. (2017) + description: "Calculation of Reflection Spectrum with Actual Layer Thickness Profile in Nacre of Akoya Pearl Oyster. Journal of Physics: Conference Series 924(1), 012011. DOI: 10.1088/1742-6596/924/1/012011. [VERIFIED] — Quantitative structural basis for orient in Akoya pearl." + - name: Read (2008) + description: "Gemmology (3rd ed.). Butterworth-Heinemann/Routledge. DOI: 10.4324/9780080507224. [APPROXIMATE] — Pearl orient mechanism, lustre distinction, species characteristics." diff --git a/docs/learn/phenomena/schiller.yaml b/docs/learn/phenomena/schiller.yaml new file mode 100644 index 0000000..f1d052c --- /dev/null +++ b/docs/learn/phenomena/schiller.yaml @@ -0,0 +1,137 @@ +title: Schiller and Peristerescence +description: Schiller and peristerescence in feldspar — the mechanism of non-spectral lamellar scattering, named species, and distinction from adularescence, labradorescence, aventurescence, and chatoyancy. +order: 10 +category: phenomena +difficulty: intermediate +icon: layers +related: + - phenomena/overview + - phenomena/adularescence + - phenomena/labradorescence + - phenomena/aventurescence + - phenomena/chatoyancy +tags: + - phenomena/schiller + - moonstone + - peristerite + - feldspar + - exsolution + +sections: + - title: Definition + content: | + Schiller (from German "Schiller," shimmer) is a broad, non-spectral, white-to-bluish + internal reflectance sheen produced by lamellar microstructure within feldspar. It arises + from coherent scattering of white light at exsolution lamellae that are too thin to produce + spectral colour separation. + + The term covers two closely related varieties: + + - **Adularescence** — the schiller of orthoclase moonstone (albite lamellae in orthoclase host) + - **Peristerescence** — the schiller of peristerite (albite–oligoclase two-phase plagioclase, An0–An16) + + Both produce a single-colour (blue or white) billowy glow, wholly distinct from the polychromatic + colour play of labradorescence. + + - title: Mechanism + content: | + Physical cause of schiller in feldspar: + subsections: + - title: Exsolution Lamellae + content: | + During slow subsolidus cooling, a single feldspar separates into alternating lamellae of + two compositionally distinct phases. In orthoclase moonstone, albite (Ab) lamellae alternate + with orthoclase (Or) at the Huttenlocher-type intergrowth. In peristerite, albite alternates + with oligoclase. + + The periodic layering has spacing on the order of visible wavelengths (approximately 60–500 nm). + + - title: Layer Thickness and Colour + content: | + - **~60–150 nm layers**: Preferential constructive interference in the blue spectral region + → prized blue schiller + - **~200–300 nm layers**: Broad white-light scattering → silver-white sheen + - **>500 nm layers**: No optical effect; stone appears transparent + + Thinner lamellae produce bluer schiller; the classic blue moonstone owes its colour to + exceptionally thin albite layers near 100 nm. + + - title: Distinction from Labradorescence + content: | + Schiller (adularescence/peristerescence) involves non-spectral, single-hue scattering. + Labradorescence, by contrast, arises from the Bøggild intergrowth at a specific plagioclase + composition (An47–An58) and produces spectrally selective, polychromatic colour play — + multiple distinct spectral colours from different zones of the stone. + + Miura, Tomisaka & Kato (1975) established the relationship between lamellae thickness and + the selectively reflected wavelengths in labradorite, confirming the structural basis for + the two distinct phenomena. + + - title: Named Species + table: + caption: Feldspar varieties showing schiller or peristerescence + headers: + - Species / Variety + - Mineral + - Layer Structure + - Visual Character + rows: + - ["Orthoclase moonstone", "Orthoclase (KAlSi₃O₈)", "Albite exsolution, ~60–150 nm for blue", "Blue to white floating billowy glow; moves with viewing angle"] + - ["Sanidine moonstone", "Sanidine (high-T K-feldspar)", "Similar exsolution; higher formation temperature", "White to cream schiller; less common"] + - ["Peristerite moonstone", "Albite–oligoclase (An0–An16)", "Two-phase plagioclase; broader lamellae", "Pale blue to white sheen; body colour often darker than orthoclase moonstone"] + - ["'Rainbow moonstone' (trade)", "Labradorite (An~50)", "Bøggild intergrowth — NOT peristerescence", "Multicolour spectral flashes; different mechanism — see labradorescence"] + + - title: Distinguishing from Related Phenomena + table: + caption: Comparison of schiller with related feldspar and inclusion-based phenomena + headers: + - Phenomenon + - Structural Cause + - Visual Signature + - Species + rows: + - ["Adularescence", "Orthoclase–albite exsolution lamellae", "Single-colour (blue/white) billowy floating glow", "Orthoclase moonstone"] + - ["Peristerescence / schiller", "Albite–oligoclase exsolution", "Single-colour (white/pale blue) sheen; often more diffuse", "Peristerite"] + - ["Labradorescence", "Bøggild intergrowth (An47–An58)", "Spectral polychromatic colour play in distinct patches", "Labradorite, spectrolite"] + - ["Aventurescence", "Metallic platelet inclusions (hematite, native copper)", "Metallic sparkle; gold/red/copper tones", "Aventurine feldspar (sunstone), aventurine quartz"] + - ["Chatoyancy", "Aligned needle/fibre inclusions", "Single bright band across cabochon; moves with rotation", "Cat's-eye chrysoberyl, many others"] + + - title: Diagnostic Relevance + content: | + Gemmological separation of moonstone varieties: + subsections: + - title: Observation Technique + content: | + Examine in reflected light over a dark background while rocking the stone slowly. + A single-colour billowy glow identifies orthoclase or peristerite moonstone (schiller/adularescence). + Multiple spectral colour flashes indicate labradorite (labradorescence). + + The schiller should appear to float just below the surface and move smoothly as the stone tilts. + + - title: Refractive Index Separation + content: | + RI provides a reliable quantitative separation: + + - Orthoclase moonstone: RI ~1.518–1.526 + - Peristerite: RI ~1.525–1.536 + - Labradorite: RI ~1.559–1.573 + + Any feldspar moonstone with RI above approximately 1.55 is likely labradorite, + not true orthoclase or peristerite moonstone. + + Birefringence also assists: orthoclase δ ~0.005–0.008; labradorite δ ~0.009–0.011. + + - title: Krzemnicki 2004 Note + content: | + Krzemnicki (2004) reported red and green labradorite from the Democratic Republic of Congo + showing spectral colour play, demonstrating that labradorescence colours vary with composition + and confirming that the distinction from schiller rests on mechanism and RI, not colour alone. + + - title: Sources + items: + - name: Miura, Tomisaka & Kato (1975) + description: "Labradorescence and the ideal behavior of thicknesses of alternate lamellae in the Bøggild intergrowth. Mineralogical Journal 7(6), 526–541. DOI: 10.2465/minerj1953.7.526. [VERIFIED]" + - name: Krzemnicki (2004) + description: "Red and green labradorite feldspar from Congo. The Journal of Gemmology 29(1), 15–23. DOI: 10.15506/jog.2004.29.1.15. [VERIFIED]" + - name: Read (2008) + description: "Gemmology (3rd ed.). Butterworth-Heinemann/Routledge. DOI: 10.4324/9780080507224. [APPROXIMATE] — Chapter 'Colour, Lustre and Sheen'; layer-thickness figures and RI values." diff --git a/docs/learn/phenomena/silk-effect.yaml b/docs/learn/phenomena/silk-effect.yaml new file mode 100644 index 0000000..53792c1 --- /dev/null +++ b/docs/learn/phenomena/silk-effect.yaml @@ -0,0 +1,128 @@ +title: Silk Effect +description: The silk effect in Kashmir sapphire and Burmese ruby — velvety appearance from rutile-needle clouds, mechanism, distinction from asterism, and diagnostic significance for origin and heat-treatment detection. +order: 11 +category: phenomena +difficulty: intermediate +icon: feather +related: + - phenomena/overview + - phenomena/asterism + - phenomena/chatoyancy +tags: + - phenomena/silk-effect + - kashmir-sapphire + - corundum + - rutile + - heat-treatment + - origin-determination + +sections: + - title: Definition + content: | + The silk effect is the soft, velvety diffuse glow visible in the body of fine Kashmir sapphires + and some Burmese rubies. It is caused by dense clouds of very fine rutile (TiO₂) needles that + scatter incident light internally, giving the stone an appearance likened to crushed velvet or + a sleepy quality. + + Silk is entirely distinct from asterism: asterism requires long, perfectly oriented needles + that concentrate light into a star; silk involves shorter, less-oriented needles at higher + density, producing overall haziness rather than a localised star pattern. + + - title: Mechanism + content: | + Physical cause of the silk effect: + subsections: + - title: Inclusion Type + content: | + Very fine, randomly or sub-randomly oriented rutile (TiO₂) needles, typically less than + 5 µm in length and less than 1 µm in diameter, often partially dissolved during + metamorphic or reheating events. In Kashmir sapphire, these may be accompanied by thin + films of boehmite (AlO(OH)) on crystal surfaces. + + - title: Optical Cause + content: | + Rayleigh/Mie scattering by a dense cloud of sub-micron needles. Because the needles are + shorter than a full visible wavelength in many cases, they scatter blue and violet light + preferentially. This diffuses light throughout the stone and reduces the windowing effect + that makes some sapphires appear dark from certain angles. + + The result is the characteristic cool, hazy blue body appearance of Kashmir sapphire — + the stone appears illuminated from within. + + Note: The Rayleigh/Mie scattering assignment is consistent with standard optics for + sub-micron particles; a dedicated peer-reviewed paper on this specific scattering + mechanism in Kashmir silk was not retrieved in the source research session. + [PARTIALLY_SUPPORTED] + + - title: Heat Treatment and Silk Dissolution + content: | + Heating above approximately 1200 °C dissolves the rutile needles back into the corundum + lattice. Loss of silk is therefore one of the primary microscopic indicators of heat + treatment in sapphire. Hänni (1990) documented that the characteristic veil-like inclusions + of Kashmir sapphire — which produce its "sleepy or velvety appearance" — are absent or + disrupted in heated material. + + - title: Named Species + table: + caption: Species and varieties showing silk + headers: + - Species + - Silk Character + - Significance + rows: + - ["Kashmir sapphire (unheated)", "Dense clouds of fine rutile needles + boehmite films; partially re-dissolved", "'Velvety' or 'sleepy' blue; highly diagnostic for unheated Kashmir origin; lost on heating"] + - ["Burmese (Mogok) ruby (unheated)", "Fine rutile silk clouds; less dense than Kashmir; iron-poor composition", "Soft pigeon's-blood red with velvety depth; partially reduced by heat treatment"] + - ["Sri Lankan sapphire (unheated)", "Rutile silk present but needles longer; more likely to produce weak asterism or chatoyancy", "Less velvety than Kashmir; coarser silk"] + - ["Thai/Cambodian corundum (typically heated)", "Silk dissolved by heat treatment; needles absent", "Clean, bright appearance but no velvety character; indicates heating"] + + - title: Distinguishing Silk from Related Phenomena + table: + caption: Silk versus asterism, chatoyancy, and adularescence + headers: + - Phenomenon + - Structural Cause + - Visual Result + rows: + - ["Silk effect", "Dense short rutile needles; Mie/Rayleigh scattering throughout body", "Velvety body glow visible face-up and in oblique light; no star"] + - ["Asterism", "Long oriented rutile needles in three directions 120° apart (corundum)", "Six-ray star concentrated under point-source light on cabochon"] + - ["Chatoyancy", "Single orientation of needles or tubes producing Mie scattering", "Single bright band across cabochon; moves with rotation"] + - ["Adularescence", "Feldspar lamellae interference scattering", "Blue floating glow in moonstone; not corundum; different host mineral"] + + - title: Diagnostic Relevance + content: | + Silk in gemmological practice: + subsections: + - title: Unheated Indicator + content: | + Presence of fine needle clouds under high-magnification darkfield illumination is a + primary indicator of an unheated corundum. Under darkfield, the needles appear as bright + scattering points rather than long parallel fibres (which would indicate potential asterism). + + The combination of silk with characteristic curved growth zones and fingerprint inclusions + is a key element in Kashmir origin determination by major laboratories (Gübelin, SSEF, GRS). + + - title: Heat Treatment Indicator + content: | + Absence of silk in a sapphire or ruby that would be expected to carry it — particularly + Kashmir and Mogok material — is strong evidence of heat treatment. Labs also look for + healed fingerprints and absence of needles in stones whose other properties (colour zone, + SG, RI) suggest a high-quality natural origin. + + Hänni (1990) remains the primary peer-reviewed reference for Kashmir sapphire diagnostic + inclusion characteristics. + + - title: Star Ruby / Silk Relationship + content: | + In star ruby, the same rutile mineral forms the inclusions, but the needles are long, + complete, and perfectly oriented in three directions 60° apart. Silk and asterism + represent two end-members of rutile inclusion development: short and dense (silk) versus + long and oriented (star). Intermediate stages produce hazy, poorly defined asterism. + + - title: Sources + items: + - name: Hänni (1990) + description: "A contribution to the distinguishing characteristics of sapphire from Kashmir. The Journal of Gemmology 22(2), 67–75. DOI: 10.15506/jog.1990.22.2.67. [VERIFIED] — Primary peer-reviewed reference for Kashmir silk inclusions and velvety appearance." + - name: Keller (1983) + description: "The Rubies of Burma: A Review of the Mogok Stone Tract. Gems & Gemology 19(4), 209–219. DOI: 10.5741/gems.19.4.209. [VERIFIED] — Documents inclusion types including silk in Mogok ruby." + - name: Read (2008) + description: "Gemmology (3rd ed.). Butterworth-Heinemann/Routledge. DOI: 10.4324/9780080507224. [APPROXIMATE] — Chapter 'Colour, Lustre and Sheen'; silk terminology and heat treatment effects." diff --git a/docs/learn/phenomena/tenebrescence.yaml b/docs/learn/phenomena/tenebrescence.yaml new file mode 100644 index 0000000..e53cfcf --- /dev/null +++ b/docs/learn/phenomena/tenebrescence.yaml @@ -0,0 +1,150 @@ +title: Tenebrescence +description: Tenebrescence — reversible photochromic colour change in hackmanite driven by S₂⁻ radical colour centres, mechanism, named species, and diagnostic distinction from the alexandrite effect and irradiation-induced colour changes. +order: 15 +category: phenomena +difficulty: advanced +icon: sun +related: + - phenomena/overview + - phenomena/colour-change + - phenomena/alexandrite-effect + - phenomena/fluorescence +tags: + - phenomena/tenebrescence + - hackmanite + - sodalite + - photochromism + - colour-centre + +sections: + - title: Definition + content: | + Tenebrescence is the reversible photochromic colour change exhibited by hackmanite (a + sulfur-bearing variety of sodalite) in which the stone is colourless to pale grey under + incandescent or ambient light, turns violet to deep purple upon brief UV or short-wavelength + visible light exposure, and then returns to colourless when placed in warm light or kept + in darkness. + + The effect is driven by the photochemical creation and annihilation of S₂⁻ radical colour + centres within the sodalite framework. It is fully reversible — the same stone can be + darkened and bleached thousands of times without degradation. + + - title: Mechanism + content: | + Physical and chemical basis of tenebrescence: + subsections: + - title: Mineral Chemistry + content: | + Hackmanite is the chromatic variety of sodalite — Na₈[Al₆Si₆O₂₄](Cl,S)₂ — in which + some Cl⁻ is replaced by the S₂⁻ disulfide radical anion. The sodalite framework + provides cage-like sites (β-cages) that host the color-active sulfur species. + + Kondo & Beaton (2009) described hackmanite from Myanmar and Afghanistan, documenting + the tenebrescent colour change: hackmanite "turns pink to purple when exposed to + sunlight or UV radiation and returns to its original colour when placed in incandescent + light or kept in the dark." + + - title: S₂⁻ Colour Centre + content: | + The S₂⁻ radical anion absorbs visible light around 530–560 nm (yellow-green), giving + the stone its purple/violet appearance — the complementary colour to yellow-green. + + In the colourless state, sulfur is present in a configuration that does not absorb + significantly in the visible range. UV exposure converts some sulfur species to S₂⁻, + creating the colour centre. Visible light or thermal energy reverses the conversion. + + Goettlicher et al. (2013) used sulfur K X-ray absorption near-edge structure (XANES) + spectroscopy to confirm the role of the polysulfide radical in the photochromic + mechanism. Radomskaya et al. (2021) further confirmed the crystal chemistry and + luminescence behaviour of natural hackmanite from Russia. + + - title: Associated Phosphorescence + content: | + After UV exposure, hackmanite shows a yellow-orange persistent afterglow as the excited + S₂⁻ centres partially relax via spin-forbidden transitions. This phosphorescence is an + associated feature of the tenebrescence cycle — both arise from the same colour centre. + See also Fluorescence and Phosphorescence for further detail. + + - title: Reversibility + content: | + The colour change is fully reversible over thousands of cycles under normal conditions. + This distinguishes tenebrescence from: + - Irradiation-induced colour changes (e.g., maxixe beryl, blue topaz) — these are + permanent or fade only slowly under prolonged light exposure + - Heat treatment effects — permanent structural changes + + - title: Named Species + table: + caption: Minerals exhibiting tenebrescence or related photochromic effects + headers: + - Mineral + - Occurrence + - Tenebrescence Character + rows: + - ["Hackmanite (sodalite var.)", "Myanmar (Sagaing Region), Afghanistan (Badakhshan), Canada (Ontario), Russia (Inagli Massif), Greenland", "Colourless/grey → violet/pink in UV; reverses under incandescent light or warming; primary tenebrescent gem species"] + - ["Tugtupite (beryllosodalite)", "Greenland", "Related photochromic effect; deep red → brighter red under UV; same S₂⁻ mechanism variant [PARTIALLY_SUPPORTED — no separate tugtupite primary paper retrieved]"] + - ["Some synthetic sodalites", "Laboratory", "Strong engineered tenebrescence; used in persistent luminescence research"] + + - title: Distinguishing Tenebrescence from the Alexandrite Effect + table: + caption: Key distinctions between tenebrescence and alexandrite-effect colour change + headers: + - Feature + - Tenebrescence + - Alexandrite Effect + rows: + - ["Reversibility", "Fully reversible by light or mild heat", "Reversible in the same sense — colour shifts immediately with light source change"] + - ["Cause", "Photochemical creation/destruction of S₂⁻ colour centre", "Fixed Cr³⁺ (or V³⁺) absorption window; colour depends on illuminant spectral power"] + - ["UV activation required?", "Yes — UV or short-wavelength visible light triggers the colour state", "No — colour change is passive, driven by visible illuminant composition only"] + - ["Mineral group", "Sodalite group (tectosilicate)", "Chrysoberyl (alexandrite), garnet, sapphire, diaspore"] + - ["State persistence", "Coloured state persists in darkness until reversed by visible light or heat", "Colour reverts immediately when illuminant changes; no residual state"] + - ["Test lamp needed?", "Yes — SWUV lamp to induce colour", "No — observe under daylight and incandescent only"] + + - title: How to Test for Tenebrescence + content: | + Standard diagnostic procedure: + subsections: + - title: Test Procedure + content: | + 1. Observe the stone under incandescent or ambient light — note colourless to pale grey + body colour. + 2. Illuminate with shortwave UV (SWUV, 254 nm) for 10–30 seconds in subdued conditions. + 3. Remove UV source and observe immediately under incandescent light — dramatic violet + to purple colour should be visible. + 4. Leave in ordinary light or warm gently — colour fades to near-colourless within + seconds to minutes. + + The effect is instantaneous and dramatic in fine material. Even in weak hackmanite, + some visible shift should occur. + + - title: Distinguishing Hackmanite from Sodalite + content: | + Hackmanite and non-sulfur sodalite are mineralogically the same species differing + only in sulfur content. Sodalite does not respond to UV in the tenebrescent manner. + + If UV exposure produces no colour change, the stone is sodalite (or another mineral + entirely). Tenebrescence is diagnostic for hackmanite within the sodalite group. + + - title: Diagnostic Relevance + content: | + Tenebrescence in gemmological practice: + + - Tenebrescence is diagnostic for hackmanite; no other commonly encountered gemstone + shows fully reversible UV-triggered colour change of this character. + + - Distinguish from irradiation-induced colour changes (e.g., maxixe beryl, blue topaz, + treated pink diamonds): irradiation-induced colours do not reverse under ordinary + daylight exposure — they are permanent or fade only under prolonged high-intensity light + or high temperature. + + - Hackmanite also shows yellow-orange phosphorescence after UV excitation — a feature + confirmed by both Kondo & Beaton (2009) and Radomskaya et al. (2021). + + - title: Sources + items: + - name: Kondo & Beaton (2009) + description: "Hackmanite/Sodalite from Myanmar and Afghanistan. Gems & Gemology 45(1), 38–43. DOI: 10.5741/gems.45.1.38. [VERIFIED] — Primary gemmological source for tenebrescence in hackmanite; documents colour change, phosphorescence, and locality characteristics." + - name: Goettlicher et al. (2013) + description: "Sulfur K X-ray absorption near edge structure spectroscopy on the photochrome sodalite variety hackmanite. Zeitschrift für Kristallographie – Crystalline Materials 228(3), 157–171. DOI: 10.1524/zkri.2013.1587. [VERIFIED] — Confirms S₂⁻ radical as photochromic agent via XANES." + - name: Radomskaya et al. (2021) + description: "Sulfur-Bearing Sodalite, Hackmanite, in Alkaline Pegmatites of the Inagli Massif. Geology of Ore Deposits 63(7). DOI: 10.1134/s1075701521070060. [VERIFIED] — Crystal chemistry, photochromism, and luminescence of Russian hackmanite."