metamorphic
Garnet Schist
Mica Schist with Almandine (Fe3Al2(SiO4)3)
Hardness 6.5-7.5 (garnets) in a softer 2-3 matrix. Color: Silvery-gray matrix with reddish-brown crystals. Luster: Pearly to submetallic mica, vitreous garnets. Structure: Foliated/Schistose.
- Color
- Silvery-gray matrix with reddish-brown crystals
- Luster
- Pearly to submetallic mica, vitreous garnets
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Physical properties
Hardness 6.5-7.5 (garnets) in a softer 2-3 matrix. Color: Silvery-gray matrix with reddish-brown crystals. Luster: Pearly to submetallic mica, vitreous garnets. Structure: Foliated/Schistose.
Formation & geological history
Formed from the regional metamorphism of shale or mudstone under intermediate to high temperatures and pressures, typically during mountain-building events in the Precambrian or Phanerozoic eons.
Uses & applications
Garnets are used as abrasives (sandpaper, waterjet cutting) and as gemstones. Schist itself is sometimes used for decorative garden stones or minor construction filler.
Geological facts
The presence of large garnet crystals (porphyroblasts) indicates the specific temperature and pressure 'grade' the rock reached during metamorphism. Schist is the second-highest grade of metamorphic rock formed from clay.
Field identification & locations
Identify by the 'sparkly' mica-rich layers that split into thin plates and the presence of embedded round, reddish garnet crystals. Found in metamorphic belts like the Appalachians or Alps.
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