metamorphic
Schist (Micaceous Schist)
Schist (comprising Muscovite/Biotite mica, Quartz, and Feldspar)
Hardness: 3.5-4 on Mohs scale; Color: Silver-grey, brownish-gold, or greenish; Luster: Pearly to sub-metallic; Crystal Structure: Foliated (schistosity); Cleavage: Perfect basal cleavage in individual mica grains; Specific Gravity: 2.7-2.9
- Hardness
- 3
- Color
- Silver-grey, brownish-gold, or greenish
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5-4 on Mohs scale; Color: Silver-grey, brownish-gold, or greenish; Luster: Pearly to sub-metallic; Crystal Structure: Foliated (schistosity); Cleavage: Perfect basal cleavage in individual mica grains; Specific Gravity: 2.7-2.9
Formation & geological history
Formed through the regional metamorphism of shale or clay-rich sedimentary rocks under intermediate temperatures and pressures. This occurs during mountain-building events (orogenies) often in the Proterozoic or Paleozoic eras.
Uses & applications
Used primarily in construction for decorative stone (paving, roofing) or as a garden stone. Highly mica-rich varieties are used as insulators in electrical displays or as filler in paint and plastics.
Geological facts
The name 'schist' comes from the Greek word 'schizein', meaning 'to split', referring to its characteristic of being easily split along the plane of its mica flakes. High-grade schist often contains garnets.
Field identification & locations
Look for a strong parallel alignment of platy minerals (mica) that causes the rock to glitter in the sun. It is commonly found in the core of old mountain ranges like the Appalachians or the Alps. Feel for a slightly greasy or flaky texture.
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