metamorphic
Schist
Mica Schist (predominantly Muscovite/Biotite)
Hardness: 3.5-4 (varies); Color: Silvery-gray, tan, or golden-brown; Luster: Pearly to sub-metallic (shimmery); Structure: Schistose foliation (visible alignment of mineral grains); Cleavage: Perfect basal cleavage in individual mica flakes.
- Hardness
- 3
- Color
- Silvery-gray, tan, or golden-brown
- Luster
- Pearly to sub-metallic (shimmery)
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Physical properties
Hardness: 3.5-4 (varies); Color: Silvery-gray, tan, or golden-brown; Luster: Pearly to sub-metallic (shimmery); Structure: Schistose foliation (visible alignment of mineral grains); Cleavage: Perfect basal cleavage in individual mica flakes.
Formation & geological history
Formed through regional metamorphism of shale or mudstone under medium-grade pressure and temperature conditions. It typically dates to periods of mountain-building (orogeny) where tectonic plates collide.
Uses & applications
Used historically as a building stone (flagstone) and decorative garden stone. Certain varieties are used as a source of industrial mica or abrasive materials.
Geological facts
The word 'schist' is derived from the Greek word 'schizein,' meaning 'to split,' referring to how easily it can be flaked into thin plates along its foliated layers.
Field identification & locations
Identify it by its distinct 'shimmer' or 'sparkle' when rotated in the sunlight due to the alignment of mica flakes. It is commonly found in metamorphic terranes like the Appalachian Mountains or the Alps.
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