metamorphic
Garnet Schist
Garnetiferous Mica Schist
Hardness: 6.5–7.5 (garnets) in a softer matrix (3–4); Color: Tan/brown matrix with dark reddish-brown garnets; Luster: Vitreous garnets, silky to pearly matrix; Structure: Foliated/Schistose texture; Cleavage: One perfect direction in mica flakes.
- Hardness
- 6
- Color
- Tan/brown matrix with dark reddish-brown garnets
- Luster
- Vitreous garnets, silky to pearly matrix
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Physical properties
Hardness: 6.5–7.5 (garnets) in a softer matrix (3–4); Color: Tan/brown matrix with dark reddish-brown garnets; Luster: Vitreous garnets, silky to pearly matrix; Structure: Foliated/Schistose texture; Cleavage: One perfect direction in mica flakes.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks (like shale) under medium to high pressure and temperature. This process aligns minerals into parallel layers and allows for the growth of porphyroblasts like garnet.
Uses & applications
Commonly used as an educational specimen in geology; garnets are used as industrial abrasives (sandpaper, waterjet cutting) or as semi-precious gemstones if high quality.
Geological facts
The presence of garnets indicates specific pressure and temperature conditions (the 'garnet zone') during the rock's formation. Large, clear garnets from schist can be faceted into jewelry, but most are opaque like those seen here.
Field identification & locations
Identify by looking for a 'shiny' or flaky foliated groundmass (mica) containing embedded, hard, dodecahedral (12-sided) red or brown crystals. It is common in mountain belts like the Appalachians or Alps.
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