metamorphic
Garnet (specifically Almandine)
Almandine - Fe3Al2(SiO4)3
Hardness: 6.5–7.5 on Mohs scale; Color: Deep red to brownish-black; Luster: Vitreous to resinous; Crystal structure: Isometric (dodecahedral); Cleavage: None (conchoidal fracture); Specific gravity: 4.1–4.3
- Hardness
- 6
- Color
- Deep red to brownish-black
- Luster
- Vitreous to resinous
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Physical properties
Hardness: 6.5–7.5 on Mohs scale; Color: Deep red to brownish-black; Luster: Vitreous to resinous; Crystal structure: Isometric (dodecahedral); Cleavage: None (conchoidal fracture); Specific gravity: 4.1–4.3
Formation & geological history
Formed through regional metamorphism of clay-rich sedimentary rocks (shale) or in igneous pegmatites. It is often found in schists and gneisses.
Uses & applications
Used widely as an abrasive in sandblasting and water-jet cutting. Higher quality specimens are cut as gemstones for jewelry. It is also the January birthstone.
Geological facts
Almandine is the most common member of the garnet group. It was historically called 'carbuncle' when cut as a cabochon. Large, well-formed crystals are highly prized by mineral collectors.
Field identification & locations
Identify by its distinctive 12-sided (dodecahedral) or 24-sided (trapezohedral) crystal habit. To find in the field, look in metamorphic schist outcrops where they often weather out as hard, round nodules.
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