spinel.yaml

id: spinel
name: Spinel
crystal_system: cubic
point_group: m3m
chemistry: MgAl2O4
category: Oxides
hardness: 8
sg: 3.58-3.61
ri: 1.712-1.740
birefringence: null
optical_character: Isotropic
dispersion: 0.02
lustre: Vitreous
cleavage: Imperfect octahedral (rarely seen)
fracture: Conchoidal
fluorescence: "Weak to moderate red (LWUV) in Cr-bearing; strong red in some"
diagnostic_features: "Isotropic; octahedral habit; lacks dichroism unlike ruby; often confused with corundum historically"
pleochroism: None
colors:
- Red
- Blue (cobalt)
- Pink
- Orange (flame spinel)
- Purple
- Violet
- Grey
- Black
- Colorless
- Colour-change
treatments:
- Heat treatment (rare)
inclusions:
- Octahedral crystals
- Fingerprints (healed fractures)
- Swallowtail twins
- Zircon with halos
- Spinel crystals
localities:
- Myanmar (Mogok)
- Sri Lanka
- Tanzania (Mahenge)
- Vietnam (Luc Yen)
- Tajikistan
- Madagascar
expressions:
- slug: octahedron
  name: Octahedron
  cdl: |
    #! Species: Spinel
    #! System: Cubic (m3m)
    #! Habit: Octahedral with octahedral inclusions
    cubic[m3m]:{111}[inclusion:octahedral]
  is_primary: true
  form_description: Octahedral habit with diagnostic octahedral inclusions (negative crystals)
  forms:
  - octahedron
- slug: macle
  name: Macle Twin
  cdl: |
    #! Species: Spinel
    #! System: Cubic (m3m)
    #! Habit: Spinel-law macle twin
    cubic[m3m]:{111}@1.0 + {100}@0.25 | twin(spinel_law)
  form_description: 'Classic spinel law twin forming a flattened triangular habit - the type example for
    this twin law. Contact twinning on {111} produces the characteristic "macle" shape, a flattened octahedron
    appearing nearly triangular in outline. This twin law is named after the mineral spinel and is also
    observed in diamond and franklinite.

    '
  forms:
  - octahedron
  - twin