metamorphic
Mica Schist
Mica Schist (predominantly Muscovite or Biotite sheet silicates)
Hardness: 3.5-4 Mohs (for the rock bulk); Color: Silvery-gray, metallic, or dark gray/brown; Luster: Pearly to submetallic; Structure: Foliated with distinct 'schistosity'; Cleavage: Basal cleavage in mineral grains leads to easy splitting into thin plates.
- Hardness
- 3
- Color
- Silvery-gray, metallic, or dark gray/brown
- Luster
- Pearly to submetallic
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Physical properties
Hardness: 3.5-4 Mohs (for the rock bulk); Color: Silvery-gray, metallic, or dark gray/brown; Luster: Pearly to submetallic; Structure: Foliated with distinct 'schistosity'; Cleavage: Basal cleavage in mineral grains leads to easy splitting into thin plates.
Formation & geological history
Formed from the regional metamorphism of shale or mudstone under intermediate to high temperatures and pressures. This creates large mineral grains (phaneritic) aligned in thin layers. Age varies by tectonic region, often associated with ancient mountain-building events.
Uses & applications
Used historically as a building stone (flagstone), in the manufacture of heat insulators, as a filler in paints and plastics, and as a decorative stone in gardening and landscaping.
Geological facts
Schist is characterized by having more than 50% platy minerals. The term 'schist' comes from the Greek word 'schizein,' meaning 'to split,' referring to its tendency to flake and break along parallel planes.
Field identification & locations
Field identification is based on the 'schistose' texture: it is highly foliated and glittery/reflective under light. Locations include the Appalachian Mountains (USA), the Alps, and the Scottish Highlands. Collectors should look for garnets or staurolites often embedded within it.
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