metamorphic
Garnet Schist
Almandine-bearing Mica Schist
Hardness: 6.5-7.5 (garnets) vs 2-3 (mica matrix); Color: Dark grey/brown matrix with reddish-pink garnet inclusions; Luster: Vitreous to sub-metallic; Structure: Foliated (schistosity); Specific gravity: Approx 2.8-4.3 depending on mineral concentration.
- Hardness
- 6
- Color
- Dark grey/brown matrix with reddish-pink garnet inclusions
- Luster
- Vitreous to sub-metallic
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Physical properties
Hardness: 6.5-7.5 (garnets) vs 2-3 (mica matrix); Color: Dark grey/brown matrix with reddish-pink garnet inclusions; Luster: Vitreous to sub-metallic; Structure: Foliated (schistosity); Specific gravity: Approx 2.8-4.3 depending on mineral concentration.
Formation & geological history
Formed through regional metamorphism of clay-rich sedimentary rocks (pelites) under intermediate to high pressure and temperature conditions, typically during mountain-building events (orogenies).
Uses & applications
Primarily used as geological specimens and for educational purposes; Almandine garnets are used industrially as abrasives for sandblasting and water-jet cutting.
Geological facts
The garnets in this rock are 'porphyroblasts,' which means they grew larger than the surrounding mineral grains during the metamorphic process. Schist is known for its 'schistosity,' the alignment of platy minerals like mica that causes it to flake.
Field identification & locations
Identify in the field by looking for a sparkly, foliated (layered) silvery-grey matrix containing hard, rounded, reddish or dark brown crystals. Commonly found in metamorphic terrains like the Appalachian or Himalayan mountains.
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