metamorphic
Mica Schist
Mica Schist (KAl2(AlSi3O10)(OH)2 / K(Mg,Fe)3AlSi3O10(OH)2 mixed with SiO2)
Hardness: 3.5-4; Color: Silver, gray, or brown with a sparkly appearance; Luster: Pearly to metallic; Crystal Structure: Monoclinic (foliated); Cleavage: Perfect basal cleavage in individual mica flakes.
- Hardness
- 3
- Color
- Silver, gray, or brown with a sparkly appearance
- Luster
- Pearly to metallic
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Physical properties
Hardness: 3.5-4; Color: Silver, gray, or brown with a sparkly appearance; Luster: Pearly to metallic; Crystal Structure: Monoclinic (foliated); Cleavage: Perfect basal cleavage in individual mica flakes.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high grades of heat and pressure. The mica crystals grow large enough to be seen by the naked eye, creating a foliated texture.
Uses & applications
Primarily used as a decorative stone in garden landscaping, flagstone for walkways, and sometimes as a filler in construction materials. Historic use in early window making (muscovite variety).
Geological facts
The 'sparkle' in schist comes from the alignment of mica minerals (muscovite or biotite) which reflect light simultaneously. It represents a higher metamorphic grade than slate or phyllite.
Field identification & locations
Identify by its 'schistosity' or layered, sparkly appearance. It feels somewhat flaky or rough and can often be crumbled with a fingernail or steel tool. Common in mountain belts like the Appalachians or Himalayas.
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