cubic Nesosilicates
Garnet (Trapezohedron)
Formula X3Y2(SiO4)3
Crystal Structure
#! Species: Garnet
#! System: Cubic (m3m)
#! Habit: Trapezohedron (icositetrahedron)
cubic[m3m]:{211}
cubic
m3m
{211}
Quick Facts
Hardness
6.5
Specific Gravity
3.5
Refractive Index
1.73
Optical Character
Isotropic
Physical Properties
- Crystal System
- cubic
- Hardness (Mohs)
- 6.5
- Specific Gravity
- 3.5
- Cleavage
- None
- Fracture
- Conchoidal to uneven
- Lustre
- Vitreous to resinous
Optical Properties
- Refractive Index
- 1.73
- Optical Character
- Isotropic
- Dispersion
- 0.027-0.057
- Pleochroism
- None (isotropic)
Characteristics
Colours
Red (almandine, pyrope)Orange (spessartine, hessonite)Yellow (grossular, topazolite)Green (demantoid, tsavorite, uvarovite)Purple (rhodolite)Brown (hessonite)Pink (rhodolite, malaya)Color-change (rare pyrope-spessartine)
Localities
IndiaSri LankaMadagascarTanzaniaBrazilMozambiqueKenyaRussia (Urals)Namibia
Common Inclusions
Silk (rutile needles)CrystalsFingerprintsGrowth tubesHorsetail (demantoid)Roiled appearance (hessonite)
Known Treatments
Heat treatment (rare)Surface coating (rare)
Crystal Forms
trapezohedron
Diagnostic Features
Isotropic; no cleavage; high SG (3.5-4.3); dodecahedral/trapezohedral habit
Related Minerals
Other minerals in the cubic system
