metamorphic
Mica Schist
Mica Schist (Composition typically includes Muscovite KAl2(AlSi3O10)(OH)2 and Quartz SiO2)
Hardness: 3.5-4 on Mohs scale; Color: Silvery-gray, brownish-gold, or bronze; Luster: Pearly to sub-metallic sparkle; Structure: Foliated (schistosity) with medium to large-grained visible plate-like crystals; Cleavage: Perfect basal cleavage in individual mica grains; Specific Gravity: 2.7-3.0.
- Hardness
- 3
- Color
- Silvery-gray, brownish-gold, or bronze
- Luster
- Pearly to sub-metallic sparkle
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Physical properties
Hardness: 3.5-4 on Mohs scale; Color: Silvery-gray, brownish-gold, or bronze; Luster: Pearly to sub-metallic sparkle; Structure: Foliated (schistosity) with medium to large-grained visible plate-like crystals; Cleavage: Perfect basal cleavage in individual mica grains; Specific Gravity: 2.7-3.0.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high temperatures and pressures. This creates a medium-grade metamorphic rock where clay minerals transform into large, visible mica flakes aligned in parallel layers. Can be hundreds of millions to billions of years old.
Uses & applications
Primarily used as a decorative stone in architecture, garden flagstones, and wall veneers. Historically, 'ground mica' from this rock has been used in joint compounds, paints, and cosmetics for its glittery effect.
Geological facts
The word 'schist' comes from the Greek 'schistos', meaning 'split', referring to its ability to be easily flaked. The sparkling 'fish-scale' appearance is the most distinctive feature and is caused by light reflecting off the large mica crystals.
Field identification & locations
Identify by its 'schistosity' (wavy or planar shiny layers) and its tendency to flake off in thin sheets when scratched. Commonly found in mountain belts like the Appalachians or Alps. To collect, look for sparkly outcrops in areas of known tectonic uplift.
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