metamorphic
Garnet (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: Cubic (Isometric); 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: Cubic (Isometric); Cleavage: None (conchoidal fracture); Specific gravity: 4.1-4.3
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks (like shale) under high pressure and temperature. Commonly found in mica schists and gneisses.
Uses & applications
Predominantly used as an abrasive in industrial sandblasting and water-jet cutting. In its gem-quality form, it is used for jewelry (faceted gems or cabochons) and as a January birthstone.
Geological facts
Garnets have been used as gemstones since the Bronze Age. The name 'Garnet' comes from the Latin 'granatus', meaning seed-like, due to their resemblance to pomegranate seeds. Almandine is the most common variety of the garnet group.
Field identification & locations
Identify in the field by its high density, lack of cleavage, and typical dodecahedral crystal habit. Often found in metamorphic belts globally, notably in India, Brazil, and the USA (New York/Idaho).
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