metamorphic
Almandine Garnet
Iron aluminum silicate - Fe3Al2(SiO4)3
Hardness: 6.5–7.5 Mohs scale. Color: Deep red, brownish-red, to dark blackish-red. Luster: Vitreous to resinous. Crystal Structure: Isometric (Dodecahedral). Cleavage: None (subconchoidal fracture). Specific gravity: 4.3.
- Hardness
- 6
- Color
- Deep red, brownish-red, to dark blackish-red
- Luster
- Vitreous to resinous
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Physical properties
Hardness: 6.5–7.5 Mohs scale. Color: Deep red, brownish-red, to dark blackish-red. Luster: Vitreous to resinous. Crystal Structure: Isometric (Dodecahedral). Cleavage: None (subconchoidal fracture). Specific gravity: 4.3.
Formation & geological history
Formed through regional metamorphism of clay-rich sedimentary rocks (shale) at high temperatures and pressures. Most frequently found in mica schists and gneisses.
Uses & applications
Commonly used in industry as an abrasive (sandpaper, waterjet cutting), and in jewelry as the most common garnet gemstone (often referred to as 'carbuncular' garnets in ancient times).
Geological facts
Garnets are the birthstone for January. Almandine is the most widespread member of the garnet group. Some specimens exhibit 'asterism' (a star-like reflection) due to needle-like inclusions of rutile.
Field identification & locations
Identify by its characteristic dodecahedral shape (even if weathered), high density, and dark red hue. Found globally in metamorphic belts; notable locations include the USA (New York/Idaho), India, and Brazil.
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