metamorphic
Garnet in Schist/Gneiss Matrix
Almandine (Fe3Al2(SiO4)3) or Pyrope (Mg3Al2(SiO4)3)
Hardness: 6.5 to 7.5; Color: Deep reddish-brown to dark brown; Luster: Vitreous to resinous; Crystal structure: Isometric (dodecahedral or trapezohedral traits often visible); Cleavage: None/Indistinct.
- Hardness
- 6
- Color
- Deep reddish-brown to dark brown
- Luster
- Vitreous to resinous
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Physical properties
Hardness: 6.5 to 7.5; Color: Deep reddish-brown to dark brown; Luster: Vitreous to resinous; Crystal structure: Isometric (dodecahedral or trapezohedral traits often visible); Cleavage: None/Indistinct.
Formation & geological history
Formed under high pressure and temperature during regional metamorphism of clay-rich sedimentary rocks (shale). Garnets grow as porphyroblasts within host rocks like schist or gneiss.
Uses & applications
Used as an abrasive in sandpaper and water-jet cutting when industrial grade; high-quality specimens are used in jewelry as gemstones; also a popular mineral specimen for collectors.
Geological facts
Garnet is the birthstone for January. Because of their hardness and resistance to chemical weathering, garnets often survive long after their host rock has eroded, ending up in river sands.
Field identification & locations
Identify by its characteristic reddish-brown color, dodecahedral crystal habits, and extreme hardness compared to the surrounding matrix. Common in metamorphic belts like the Appalachians or the Alps.
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