metamorphic
Mica Schist
Mica Schist (primarily Muscovite and Biotite micas)
Hardness: 3.5–4.0; Color: Silvery-gray, brownish, or black; Luster: Pearly to sub-metallic; Crystal Structure: Monoclinic (plate-like grains); Cleavage: Perfect basal cleavage in individual flakes; Specific Gravity: 2.7–3.0
- Hardness
- 3
- Color
- Silvery-gray, brownish, or black
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5–4.0; Color: Silvery-gray, brownish, or black; Luster: Pearly to sub-metallic; Crystal Structure: Monoclinic (plate-like grains); Cleavage: Perfect basal cleavage in individual flakes; Specific Gravity: 2.7–3.0
Formation & geological history
Formed through regional metamorphism of shale or mudstone under intermediate to high temperature and pressure. It is characterized by 'schistosity,' the alignment of flattened mineral grains.
Uses & applications
Used as building stone, decorative garden stones, and an source of mica for electrical insulation and decorative glitter in cosmetics. Historically used for roofing and wall flagging.
Geological facts
Mica schist is famous for its 'sparkle.' Under the right conditions, it can contain large inclusion crystals known as porphyroblasts, most commonly Almandine garnets.
Field identification & locations
Identify in the field by its distinct foliation and 'sparkle' when turned in the light; it easily flakes apart into thin sheets with a knife. Found globally in mountain belts like the Appalachians, Alps, and Himalayas.
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