metamorphic
Biotite–quartz schist
Mica schist, chiefly quartz (SiO₂), biotite mica, feldspar, and minor opaque minerals
AI-generated identification · may be incorrectTypically medium- to coarse-grained with strong foliation and glittering platy mica; gray to black, with vitreous quartz and pearly biotite. Quartz hardness 7, biotite 2.5–3; specific gravity commonly 2.7–2.9; mica has perfect basal cleavage.
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Physical properties
Typically medium- to coarse-grained with strong foliation and glittering platy mica; gray to black, with vitreous quartz and pearly biotite. Quartz hardness 7, biotite 2.5–3; specific gravity commonly 2.7–2.9; mica has perfect basal cleavage.
Formation & geological history
Formed when shale or other clay-rich sediment underwent regional metamorphism, recrystallizing under directed pressure roughly 300–650°C. Its exact age cannot be determined from the image and depends on the locality.
Uses & applications
Used locally as decorative stone, landscaping material, wall cladding, and aggregate, though its foliation limits structural use; attractive pieces are collected but are rarely high-value.
Geological facts
The silvery sparkle comes from aligned mica flakes, while dark lenses may be biotite or amphibole. Foliation records deformation during mountain-building.
Field identification & locations
Identify by its layered, easily splitting fabric and abundant reflective mica, unlike massive granite; common in regional metamorphic belts worldwide, including the Appalachians, Alps, and Himalayas.
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