metamorphic
Garnet Schist
Garnetiferous Mica Schist
Hardness: 6-7.5 (due to garnet grains within softer mica matrix around 2.5-3). Color: Yellowish-brown, tan, and rusty orange matrix with dark reddish-brown to black porphyroblasts. Luster: Vitreous on garnets, silky or pearly on schistose mica bands. Cleavage: Foliated cleavage along schistosity planes.
- Hardness
- 6-7
- Luster
- Vitreous on garnets, silky or pearly on schistose mica bands
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Physical properties
Hardness: 6-7.5 (due to garnet grains within softer mica matrix around 2.5-3). Color: Yellowish-brown, tan, and rusty orange matrix with dark reddish-brown to black porphyroblasts. Luster: Vitreous on garnets, silky or pearly on schistose mica bands. Cleavage: Foliated cleavage along schistosity planes.
Formation & geological history
Formed through medium-grade regional metamorphism of shale, mudstone, or clay-rich sedimentary rocks under elevated temperatures and pressures, typically during mountain-building events (orogenies).
Uses & applications
Used primarily as decorative stone, landscaping material, educational specimens, and source material for industrial abrasives (garnet content).
Geological facts
The reddish dark spots visible throughout the layered fabric are porphyroblasts—individual garnet crystals that grew inside the rock as it underwent intense heat and pressure.
Field identification & locations
Identified by distinct wavy layering (foliated schistosity) interspersed with rounded, dark garnet crystals. Commonly found in metamorphic terranes worldwide, such as the Appalachian Mountains.
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