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
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Open in PlaygroundPhysical 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
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