metamorphic
Schist
Crystalline Metamorphic Rock (Schistose)
Hardness: 3.5-5 (Mohs scale); Color: Silvery-gray, greenish, or brown; Luster: Pearly to sub-metallic due to mica; Crystal structure: Foliated with visible mineral grains; Cleavage: Excellent basal cleavage in mica components; Specific Gravity: 2.7-3.0.
- Hardness
- 3
- Color
- Silvery-gray, greenish, or brown
- Luster
- Pearly to sub-metallic due to mica
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Physical properties
Hardness: 3.5-5 (Mohs scale); Color: Silvery-gray, greenish, or brown; Luster: Pearly to sub-metallic due to mica; Crystal structure: Foliated with visible mineral grains; Cleavage: Excellent basal cleavage in mica components; Specific Gravity: 2.7-3.0.
Formation & geological history
Formed through the regional metamorphism of shale, mudstone, or igneous rocks under medium-grade temperature and pressure conditions. This specific specimen has been water-worn into a cobble shape, likely in a river or glacial environment.
Uses & applications
Used occasionally as decorative stone in construction, garden landscaping, and as a source for industrial minerals like mica or graphite. Not typically used in jewelry unless it contains garnets.
Geological facts
Schist is characterized by 'schistosity,' where individual mineral grains (like mica or chlorite) are large enough to be seen with the naked eye and are aligned in parallel layers. The name comes from the Greek word 'schizein,' meaning 'to split.'
Field identification & locations
Identify in the field by its distinct foliated layers and shiny, platelike minerals that sparkle in the sun. Commonly found in mountainous regions or glacial till. Look for the 'grain' of the rock which allows it to split into thin plates.
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