metamorphic
Mica Schist
Mica Schist (predominantly Muscovite or Biotite sheet silicates)
Hardness: 2-3 (Mohs scale); Color: silvery-gray, gold-brown, or dark gray; Luster: Pearly to sub-metallic; Crystal Structure: Monoclinic, typically found in foliated sheet-like layers; Cleavage: Perfect basal cleavage; Specific Gravity: 2.8 - 3.2.
- Hardness
- 2-3 (Mohs scale)
- Color
- silvery-gray, gold-brown, or dark gray
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 2-3 (Mohs scale); Color: silvery-gray, gold-brown, or dark gray; Luster: Pearly to sub-metallic; Crystal Structure: Monoclinic, typically found in foliated sheet-like layers; Cleavage: Perfect basal cleavage; Specific Gravity: 2.8 - 3.2.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high pressure and temperature. The mica flakes align perpendicularly to the direction of pressure, creating the characteristic schistosity. It is found in mountain ranges formed by tectonic plate collisions.
Uses & applications
Used historically as a decorative building stone or 'glitter' in early plasters. Today, it is used in construction as fill material or garden landscaping stones. Select mica minerals are used in electrical insulation and cosmetics.
Geological facts
The word 'schist' is derived from the Greek word 'schizein,' meaning 'to split,' referring to how easily the rock can be cleaved along its mineral layers. It is the middle stage of metamorphism between phyllite and gneiss.
Field identification & locations
Identify in the field by its 'shimmer' or 'sparkle' in sunlight and its tendency to flake off into thin, silvery bits when scratched. It is commonly found in the Appalachian Mountains, Scandinavia, and the Alps. Collectors look for garnet inclusions which are common in mica schist.
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