Silicates — garnet group · Sourced PROFILE
Garnet group
X₃Y₂(SiO₄)₃
A family of cubic silicates sharing one structure but spanning several compositions and many gemstone colours.
AT A GLANCE
- Formula
- X₃Y₂(SiO₄)₃
- Crystal system
- Cubic
- Space group
- Ia̅3d (representative garnet structure)
- Mohs hardness
- 6.5–7.5
- Density
- Common gem garnets roughly 3.5–4.3 g/cm³ depending on species
- Optical character
- Isotropic
CRYSTALLOGRAPHY
Crystal form & structure
Typically dodecahedral or trapezohedral crystals; also granular or massive. This group profile uses almandine as a representative reference.
HAND-SAMPLE PROPERTIES
Physical properties
- Cleavage
- None
- Fracture
- Conchoidal to uneven
- Tenacity
- Brittle
- Streak
- White
- Luster
- Vitreous to resinous
- Transparency
- Transparent to opaque
- Observed colours
- Red, orange, yellow, green, purple, brown, black or colourless
LIGHT & OPTICS
Optical properties
- Optical class
- Isotropic
- Refractive index
- n commonly about 1.73–1.89 across the group
- Fluorescence & electrical behaviour
- Usually inert to variable; fluorescence is not a group-level diagnostic.
GEOLOGICAL SETTING
Formation
Common in metamorphic rocks and also present in igneous rocks, skarns, and sediment derived from garnet-bearing sources.
MINERAL COMPANY
Common associations
Micas, quartz, feldspars, kyanite, sillimanite, pyroxenes, amphiboles and calcite depending on species and setting
FIELD NOTES
How to identify it
Equant dodecahedral habit, absent cleavage, relatively high hardness and density are useful clues; refractive index and chemistry are needed to identify the garnet species.
NAME & HISTORY
Where the name comes from
From Latin granatus, grain-like, referring to rounded crystals resembling seeds.
SCIENTIFIC SOURCE
Handbook of Mineralogy — Almandine (representative garnet species)
External reference; factual profile paraphrased and attributed. Copyright remains with the publisher.
PROVENANCE
Documented occurrences
Sokhcharv valley, Rushan district, Western Pamir · Pinkish almandine forms well-shaped single and clustered crystals, mostly 1 mm to 1 cm and up to about 7 cm, in garnet-bearing schist horizons. The record stays at regional precision.
Sourced · Region precisionMineralogy of garnet-containing horizons, Sokhcharv valley, Western Pamir (Vatanbekov, Zhou, Yogibekov, Gurminjova, 2020)