cubic Nesosilicates
Colour-Change Garnet (Combination)
Formula (Mg,Mn)3Al2(SiO4)3
Crystal Structure
#! Species: Colour-Change Garnet (pyrope-spessartine)
#! System: Cubic (m3m)
#! Habit: Dodecahedron-trapezohedron combination
cubic[m3m]:{110}@1.0 + {211}@0.5
cubic
m3m
{110} {211}
Quick Facts
Hardness
7.0
Specific Gravity
3.65
Refractive Index
1.74
Optical Character
Isotropic
Physical Properties
- Crystal System
- cubic
- Hardness (Mohs)
- 7.0
- Specific Gravity
- 3.65
- Cleavage
- None
- Fracture
- Conchoidal to uneven
- Lustre
- Vitreous
Optical Properties
- Refractive Index
- 1.74
- Optical Character
- Isotropic
- Dispersion
- 0.022-0.027
- Pleochroism
- None (isotropic)
Characteristics
Colours
Blue-green (daylight)Purplish-red (incandescent)Green to red change
Localities
MadagascarTanzaniaSri LankaKenyaNorway
Common Inclusions
Rutile needlesCrystal inclusionsFingerprints
Known Treatments
None commonly applied
Crystal Forms
dodecahedrontrapezohedron
Diagnostic Features
Alexandrite-like colour change (daylight green/blue to incandescent red/purple); pyrope-spessartine composition
Notes
Vanadium and chromium cause the colour-change effect
