metamorphic
Garnet-Mica Schist
Garnetiferous Porphyroblastic Schist
Hardness: 6.5-7.5 (garnets) and 2-3 (mica/matrix); Color: Tan/yellowish matrix with dark red to black inclusions; Luster: Vitreous to sub-metallic inclusions in a pearly to earthy matrix; Crystal structure: Isometric (garnets) in a foliated schistose matrix; Cleavage: None (garnets), perfect basal (mica).
- Hardness
- 6
- Color
- Tan/yellowish matrix with dark red to black inclusions
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Physical properties
Hardness: 6.5-7.5 (garnets) and 2-3 (mica/matrix); Color: Tan/yellowish matrix with dark red to black inclusions; Luster: Vitreous to sub-metallic inclusions in a pearly to earthy matrix; Crystal structure: Isometric (garnets) in a foliated schistose matrix; Cleavage: None (garnets), perfect basal (mica).
Formation & geological history
Formed from the regional metamorphism of clay-rich sedimentary rocks (pelites) under high temperature and pressure conditions, typically during mountain-building events (orogeny). Age varies widely depending on the geological setting of the find.
Uses & applications
Used in educational sets, as geological specimens for collectors, and occasionally as structural stone or source for industrial abrasives if garnet content is high.
Geological facts
The dark, rounded spots (porphyroblasts) are likely almandine garnets that grew larger than the surrounding mineral grains during the metamorphic process. Schist is a medium-grade metamorphic rock characterized by 'schistosity', or the alignment of platy grains.
Field identification & locations
Identify in the field by looking for distinct, hard, rounded crystals protruding from a flaky or layered (foliated) rock surface. Commonly found in metamorphic belts like the Appalachians or the Alps. Using a hand lens should reveal the dodecahedral shape of the crystals.
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