metamorphic
Garnet Schist
Almandine Garnet-bearing Mica Schist
Hardness: 6.5-7.5 (garnets) and 2-3 (mica matrix). Color: Silver-grey to green matrix with deep reddish-brown or black garnets. Luster: Vitreous garnets in a pearly/sub-metallic matrix. Structure: Foliated schistose texture with porphyroblasts.
- Hardness
- 6
- Luster
- Vitreous garnets in a pearly/sub-metallic matrix
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Physical properties
Hardness: 6.5-7.5 (garnets) and 2-3 (mica matrix). Color: Silver-grey to green matrix with deep reddish-brown or black garnets. Luster: Vitreous garnets in a pearly/sub-metallic matrix. Structure: Foliated schistose texture with porphyroblasts.
Formation & geological history
Formed through regional metamorphism of clay-rich sedimentary rocks (pelites) or volcanic rocks under medium-to-high pressure and temperature conditions, typically during orogenic (mountain-building) events.
Uses & applications
Large garnet crystals are used as gemstones or abrasives. The rock itself is sometimes used as decorative stone or road aggregate, though its schistosity makes it prone to splitting.
Geological facts
Garnets in schist are typical index minerals used by geologists to determine the metamorphic grade (intensity) a rock has experienced. The 'red spots' are often dodecahedral crystals that grew within the solid rock during heating.
Field identification & locations
Identify in the field by looking for a sparkly, flaky matrix (mica) containing hard, rounded, dark red or brown crystals. Found in metamorphic belts like the Appalachians, Alps, and Himalayas. Areas like the Gore Mountain in NY are famous for specimens.
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