metamorphic
Mica Schist
Mica Schist
Hardness: 3.5-4 (Mohs scale); Color: Silvery-gray, black, or brown; Luster: Pearly to sub-metallic; Crystal structure: Tabular/Platy (foliated); Cleavage: Perfect basal cleavage in individual mica grains; Specific gravity: 2.7-2.8
- Hardness
- 3
- Color
- Silvery-gray, black, or brown
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5-4 (Mohs scale); Color: Silvery-gray, black, or brown; Luster: Pearly to sub-metallic; Crystal structure: Tabular/Platy (foliated); Cleavage: Perfect basal cleavage in individual mica grains; Specific gravity: 2.7-2.8
Formation & geological history
Formed from 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 a foliated texture. It typically dates from the Precambrian to more recent orogenic events.
Uses & applications
Used as filler in paints and plastics, as a lubricant, in electronics (due to thermal resistance), and occasionally as decorative stone or construction aggregate.
Geological facts
Schist is characterized by 'schistosity,' which is the alignment of platy minerals making the rock easy to split into thin layers. The word 'schist' is derived from the Greek word 'schizein,' meaning 'to split.'
Field identification & locations
Identify by its sparkling, 'glitter-like' appearance and visible foliation. It often feels slightly greasy or rough and will flake if scratched with a knife. Common in mountain belts like the Appalachians, Alps, and Himalayas.
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