metamorphic
Mica Schist
Crystalline Schist (often primarily Muscovite or Biotite sheet silicates)
Hardness: 3.5-4 on Mohs scale; Color: Silvery-gray, brown, or golden-tan; Luster: Pearly to sub-metallic (shimmery); Structure: Foliated (schistosity) with visible large mineral grains; Cleavage: Perfect basal cleavage in individual mica flakes.
- Hardness
- 3
- Color
- Silvery-gray, brown, or golden-tan
- Luster
- Pearly to sub-metallic (shimmery)
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Physical properties
Hardness: 3.5-4 on Mohs scale; Color: Silvery-gray, brown, or golden-tan; Luster: Pearly to sub-metallic (shimmery); Structure: Foliated (schistosity) with visible large mineral grains; Cleavage: Perfect basal cleavage in individual mica flakes.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high temperatures and pressures. This transformation typically occurs during mountain-building events (orogenies) often spanning hundreds of millions of years.
Uses & applications
Used historically as a building stone and for decorative garden paths. Industrial grades of the mica within are used in electrical insulators, ground mica for paints, and in the cosmetics industry for 'shimmer' effects.
Geological facts
The word 'schist' is derived from the Greek word 'schistos,' meaning 'to split,' referring to how easily the rock can be flaked into thin layers. Large mica flakes in schist are often referred to as 'books' because they peel like pages.
Field identification & locations
Identify in the field by its distinct 'glittery' or 'sparkly' appearance and its tendency to flake off into small, flat, shiny pieces when scratched. It is common in mountainous regions like the Appalachians or the Alps. Look for wavy foliation layers.
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