metamorphic
Schist (specifically Mica Schist)
Mica Schist (primarily composed of Muscovite KAl2(AlSi3O10)(OH)2 and Biotite)
Hardness: 3.5–4.0; Color: Silvery-gray to brownish-gold; Luster: Pearly to metallic (sub-metallic); Crystal structure: Monoclinic (in individual mica flakes); Cleavage: Perfect basal cleavage (easily peels into flakes); Specific Gravity: 2.7–3.0.
- Hardness
- 3
- Color
- Silvery-gray to brownish-gold
- Luster
- Pearly to metallic (sub-metallic)
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Physical properties
Hardness: 3.5–4.0; Color: Silvery-gray to brownish-gold; Luster: Pearly to metallic (sub-metallic); Crystal structure: Monoclinic (in individual mica flakes); Cleavage: Perfect basal cleavage (easily peels into flakes); Specific Gravity: 2.7–3.0.
Formation & geological history
Formed by regional metamorphism of clay-rich sedimentary rocks like shale or mudstone under intermediate to high temperatures and pressures. This creates the characteristic 'schistosity' or foliation through the alignment of flat mica minerals.
Uses & applications
Used historically as a decorative stone in architecture and flagstone. In industry, it can be crushed for construction fill or used as a source for certain minerals like graphite or garnet if present in high concentrations.
Geological facts
Because schist is so heavily foliated, it often breaks effortlessly into thin plates. It is a common source of garnets and often hosts 'staurolite' or 'kyanite' crystals which are popular with mineral collectors.
Field identification & locations
Identify in the field by its distinct glittering or shiny appearance (due to mica) and its tendency to flake or peel when scratched with a knife. It is common in mountain belts like the Appalachians, Alps, and Himalayas.
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