metamorphic
Biotite schist
Mica schist; chiefly quartz, feldspar, and biotite mica
AI-generated identification · may be incorrectTypically gray to brown, sparkly, and strongly foliated, with visible platy mica; quartz and feldspar add granular grains. Hardness is about 2.5–3 for biotite and 6–7 for quartz; cleavage is excellent in mica, with a generally flaky crystal texture.
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Physical properties
Typically gray to brown, sparkly, and strongly foliated, with visible platy mica; quartz and feldspar add granular grains. Hardness is about 2.5–3 for biotite and 6–7 for quartz; cleavage is excellent in mica, with a generally flaky crystal texture.
Formation & geological history
Formed when shale or other clay-rich sedimentary rock underwent medium-grade regional metamorphism, causing minerals to recrystallize and align. Ages vary widely, commonly Precambrian to Paleozoic depending on the terrain.
Uses & applications
Used locally as decorative stone, landscaping material, and limited building stone, though foliation can make it split or weather easily. Attractive specimens are collected for their glittering mica texture.
Geological facts
The specimen’s glitter and layered appearance are characteristic of mica-rich schist rather than granite. Biotite may weather to rusty brown, while aligned mica flakes produce the rock’s schistosity.
Field identification & locations
Identify it by its visible foliation, abundant reflective flakes, and ability to split along mica-rich layers; unlike slate, its crystals are visibly coarse. Common in regional metamorphic belts, including the Appalachian Mountains, New England, Scandinavia, and the Himalayas.
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