metamorphic
Garnet Schist
Almandine Garnet Schist
Hardness: 6.5-7.5 (garnets), 5.5-6 (matrix); Color: Tan/brown matrix with dark reddish-brown inclusions; Luster: Vitreous to sub-vitreous garnets in a dull/pearly matrix; Structure: Foliated with porphyroblastic garnets.
- Hardness
- 6
- Color
- Tan/brown matrix with dark reddish-brown inclusions
- Luster
- Vitreous to sub-vitreous garnets in a dull/pearly matrix
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Physical properties
Hardness: 6.5-7.5 (garnets), 5.5-6 (matrix); Color: Tan/brown matrix with dark reddish-brown inclusions; Luster: Vitreous to sub-vitreous garnets in a dull/pearly matrix; Structure: Foliated with porphyroblastic garnets.
Formation & geological history
Formed through the regional metamorphism of clay-rich sedimentary rocks (pelites) like shale. The high pressure and temperature during mountain-building events cause the minerals to recrystallize, growing larger garnet crystals within a foliated schistose matrix.
Uses & applications
Used primarily as decorative specimens for collectors; garnets are also used industrially as abrasives in sandblasting and waterjet cutting.
Geological facts
The dark spots seen in this specimen are garnet crystals, specifically porphyroblasts, which grew larger than the surrounding minerals during metamorphism. Garnet is the state mineral of several US states including New York and Connecticut.
Field identification & locations
Identify by noticing the hard, reddish-brown equidimensional crystals embedded in a softer, layered, or sandy-textured matrix. Often found in riverbeds near metamorphic mountain ranges.
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