![Schist (Mica Schist (primarily Muscovite [KAl2(AlSi3O10)(OH)2] or Biotite)) — metamorphic](https://media.rockidentification.com/0e800ef9-24ba-40db-af6d-9721fa8d4590-compressed.jpg)
metamorphic
Schist
Mica Schist (primarily Muscovite [KAl2(AlSi3O10)(OH)2] or Biotite)
Hardness: 3.5–4 on Mohs scale; Color: Silvery-gray to brownish-gray; Luster: Pearly to sub-metallic; Crystal Structure: Foliated; Cleavage: Perfect in one direction (basal); Specific Gravity: 2.7–2.8
- Hardness
- 3
- Color
- Silvery-gray to brownish-gray
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5–4 on Mohs scale; Color: Silvery-gray to brownish-gray; Luster: Pearly to sub-metallic; Crystal Structure: Foliated; Cleavage: Perfect in one direction (basal); Specific Gravity: 2.7–2.8
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate pressure and temperature conditions. It typically dates from the Precambrian to Cenozoic eras, depending on the mountain-building event.
Uses & applications
Historically used for flagstone, roofing, and heat-resistant lining in stoves. Today, it is primarily used as decorative garden stone, filler in concrete, or as source material for mica in electrical insulation.
Geological facts
Schist is characterized by 'schistosity,' which is the alignment of platy minerals that allows the rock to be split into thin flakes. It often contains 'porphyroblasts'—large crystals of garnet or staurolite embedded in the mica matrix.
Field identification & locations
Identify in the field by its sparkly, 'glittery' appearance under sunlight and its tendency to flake off in thin, brittle layers. Found in the core of most major mountain ranges like the Appalachians, Alps, and Himalayas.
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