metamorphic
Schist
Mica Schist (predominantly Muscovite or Biotite)
Hardness: 3.5 - 4 (on Mohs scale); Color: Silvery-gray, golden-yellow, or brown due to iron staining; Luster: Pearly to sub-metallic; Crystal structure: Flat, sheet-like grains; Cleavage: Excellent basal cleavage in individual mica grains; Specific gravity: 2.7 - 2.8.
- Hardness
- 3
- Color
- Silvery-gray, golden-yellow, or brown due to iron staining
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5 - 4 (on Mohs scale); Color: Silvery-gray, golden-yellow, or brown due to iron staining; Luster: Pearly to sub-metallic; Crystal structure: Flat, sheet-like grains; Cleavage: Excellent basal cleavage in individual mica grains; Specific gravity: 2.7 - 2.8.
Formation & geological history
Formed by regional metamorphism of shale or mudstone at medium grades (higher pressure and temperature than slate or phyllite). Typically dates from various Precambrian to Cenozoic orogenies where plate tectonics cause mountain building.
Uses & applications
Used as decorative stone in landscaping, flagstone for walkways, and occasionally as a source of mica for electrical insulation or glitter in cosmetics and paints.
Geological facts
The word 'schist' is derived from the Greek word 'schizein', meaning 'to split', referring to its characteristic 'schistosity' which allows it to pull apart into thin plates. It represents a specific stage in the metamorphic sequence: Slate -> Phyllite -> Schist -> Gneiss.
Field identification & locations
Identify in the field by its distinct foliated texture (schistosity) and a sparkly, reflective surface caused by parallel alignment of mica flakes. It is commonly found in core regions of mountain ranges like the Appalachians, Alps, and Himalayas. To identify, look for rock that glitters in the sun and peels into thin, brittle layers when struck.
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