metamorphic
Mica Schist
Mica Schist (primarily Muscovite and Biotite phyllosilicates)
Hardness: 3.5–4 on Mohs scale; Color: Silvery-gray to brownish-black with a high metallic sheen; Luster: Pearly to sub-metallic; Structure: Foliated (schistosity) with medium to coarse grains; Cleavage: Perfect basal cleavage in individual mica grains; Specific gravity: 2.7–3.0
- Hardness
- 3
- Color
- Silvery-gray to brownish-black with a high metallic sheen
- Luster
- Pearly to sub-metallic
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Physical properties
Hardness: 3.5–4 on Mohs scale; Color: Silvery-gray to brownish-black with a high metallic sheen; Luster: Pearly to sub-metallic; Structure: Foliated (schistosity) with medium to coarse grains; Cleavage: Perfect basal cleavage in individual mica grains; Specific gravity: 2.7–3.0
Formation & geological history
Formed through the regional metamorphism of shale or mudstone at intermediate temperatures and pressures. This process aligns platy minerals like micas perpendicular to the direction of pressure, creating distinct layering. Most specimens date from the Proterozoic or Paleozoic eras.
Uses & applications
Used historically as a building stone and for decorative purposes. Mica itself is utilized in electrical insulation, paints, and cosmetics for its glittery appearance. Schist is occasionally used as a filler in construction aggregate or as decorative landscape rock.
Geological facts
Schist is characterized by 'schistosity,' which means it can be easily split into thin flakes or slabs. The word 'schist' comes from the Greek word 'schizein,' meaning 'to split.' It often contains accessory minerals like garnets, which may be found embedded within the mica layers.
Field identification & locations
Identify in the field by its distinct 'glittering' or 'sparkly' appearance under sunlight and its tendency to flake off in thin, shiny scales when scratched. Commonly found in mountain ranges such as the Appalachians, the Alps, and the Himalayas. For collectors, look for specimens containing visible red garnet inclusions.
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