metamorphic
Mica Schist
Mica Schist (contains Muscovite KAl2(AlSi3O10)(OH)2)
Hardness: 2-2.5 for mica flakes, 6-7 for the rock mass; Color: silvery gray to brown; Luster: Pearly to metallic (vitreous); Crystal Structure: Monoclinic (sheets); Cleavage: Perfect basal cleavage in mica flakes; Specific Gravity: 2.8-3.0.
- Hardness
- 2-2
- Color
- silvery gray to brown
- Luster
- Pearly to metallic (vitreous)
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Physical properties
Hardness: 2-2.5 for mica flakes, 6-7 for the rock mass; Color: silvery gray to brown; Luster: Pearly to metallic (vitreous); Crystal Structure: Monoclinic (sheets); Cleavage: Perfect basal cleavage in mica flakes; Specific Gravity: 2.8-3.0.
Formation & geological history
Formed through the regional metamorphism of shale or mudstone under intermediate to high temperatures and pressures. This process aligns platy minerals into parallel layers, a texture known as schistosity.
Uses & applications
Used historically as a building stone, for decorative flagstones, and as a source of mica for industrial electrical insulation and glitter in cosmetics.
Geological facts
The word schist comes from the Greek word 'schistos,' meaning 'split,' referring to the ease with which the rock can be divided into thin plates. It is a key indicator of the tectonic history of mountain ranges.
Field identification & locations
Identified in the field by its distinct foliation (layering) and the strong sparkle of mica flakes when turned in the light. Commonly found in metamorphic belts like the Appalachians or the Alps.
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