metamorphic
Schist
Mica Schist
Hardness: 3.5–4.0; Color: Silvery-gray, greenish, or brownish; Luster: Pearly to sub-metallic due to mica; Crystal structure: Protosilicate layers; Cleavage: Excellent in one direction (foliation/schistosity); Specific gravity: 2.7–2.8
- Hardness
- 3
- Color
- Silvery-gray, greenish, or brownish
- Luster
- Pearly to sub-metallic due to mica
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Physical properties
Hardness: 3.5–4.0; Color: Silvery-gray, greenish, or brownish; Luster: Pearly to sub-metallic due to mica; Crystal structure: Protosilicate layers; Cleavage: Excellent in one direction (foliation/schistosity); Specific gravity: 2.7–2.8
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high pressure and temperature. It is typical of Phanerozoic and Precambrian mountain-building environments.
Uses & applications
Historically used for decorative flagstone, roof tiles, and interior wall finishes. In modern industry, it is primarily used as a source of industrial minerals (like mica or garnet) and as construction aggregate.
Geological facts
The word 'schist' is derived from the Greek word 'schizein', meaning 'to split', referring to how easily the rock can be cleaved along its foliated planes. It is the intermediate stage between phyllite and gneiss.
Field identification & locations
Identify by its 'schistosity'—the alignment of visible mica grains that create a wavy, glittery appearance. Found globally in mountainous regions such as the Appalachian or Alpine ranges. Collectors look for accessory minerals like Garnet or Staurolite embedded within.
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