cubic Nesosilicates
Colour-Change Garnet (Combination)
(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 Systemcubic
Hardness (Mohs)7.0
Specific Gravity3.65
CleavageNone
FractureConchoidal to uneven
LustreVitreous
Optical Properties
Refractive Index1.74
Optical CharacterIsotropic
Dispersion0.022-0.027
PleochroismNone (isotropic)
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
