Rock Identifier
Almandine Garnet (Fe3Al2(SiO4)3) — gemstone
gemstone

Almandine Garnet

Fe3Al2(SiO4)3

Hardness: 6.5-7.5 on Mohs scale, Color: Dark red to brownish-red or purplish-red, Luster: Vitreous to resinous, Crystal Structure: Isometric (cubic), Cleavage: None (distinct parting sometimes present), Specific Gravity: 3.9-4.3

Hardness
6
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Physical properties

Hardness: 6.5-7.5 on Mohs scale, Color: Dark red to brownish-red or purplish-red, Luster: Vitreous to resinous, Crystal Structure: Isometric (cubic), Cleavage: None (distinct parting sometimes present), Specific Gravity: 3.9-4.3

Formation & geological history

Forms in metamorphic rocks such as mica schists and gneisses via regional metamorphism, as well as in certain igneous rocks like granitic pegmatites.

Uses & applications

Widely used in fine jewelry as a faceted gemstone, as well as in industrial applications such as waterjet cutting and abrasive sandblasting.

Geological facts

Garnets have been used as gemstones since the Bronze Age. Almandine is the most common and widely distributed of the garnet group minerals.

Field identification & locations

Identified by its characteristic deep red to purplish color, high refractive index, isometric crystal habit (often dodecahedral when rough), and lack of cleavage. Found worldwide including India, Brazil, and the USA.