metamorphic
Mica Schist
Mica Schist (Composition typically contains Muscovite: KAl2(AlSi3O10)(OH)2 or Biotite: K(Mg,Fe)3AlSi3O10(OH)2 along with Quartz and Feldspar)
Hardness: 3.5-4 (varies with quartz content); Color: Silvery-gray to brown/black with a pearly to metallic luster; Texture: Foliated (schistosity) with visible large mineral grains; Structure: Parallel alignment of platy mica flakes.
- Hardness
- 3
- Color
- Silvery-gray to brown/black with a pearly to metallic luster
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Physical properties
Hardness: 3.5-4 (varies with quartz content); Color: Silvery-gray to brown/black with a pearly to metallic luster; Texture: Foliated (schistosity) with visible large mineral grains; Structure: Parallel alignment of platy mica flakes.
Formation & geological history
Formed through the regional metamorphism of pelitic sedimentary rocks (shales or mudstones) under intermediate-grade conditions (medium pressure and temperature). It typically originates in mountain-building (orogenic) belts.
Uses & applications
Used historically as a building stone and for walkways. Today, it is used for decorative garden stones, high-end countertops (rarely), and as a filler in plaster and paints. The mica minerals themselves are used in electronics and cosmetics.
Geological facts
The word 'schist' is derived from the Greek word 'schistos,' meaning 'to split,' referring to how easily the rock can be flakes along its layers. It represents a higher grade of metamorphism than slate or phyllite.
Field identification & locations
Identify in the field by its distinct 'shimmer' or 'glitter' when held in the light and its ability to be flaked apart with a knife or fingernail. It is common in the Appalachian Mountains (USA) and the Scottish Highlands. Collectors look for accessory minerals like Almandine Garnet often embedded within.
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