metamorphic

Biotite-rich schist

Mica schist; predominantly biotite mica with quartz and feldspar

AI-generated identification · may be incorrect

Typically dark gray to black, strongly foliated, and sparkly with platy mica cleavage; hardness about 2.5–3 for biotite and 6–7 for quartz, with a pearly to glassy luster. The specimen appears coarse-grained and flaky, though exact identification from a photograph is provisional.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Forms when shale or other clay-rich sediment is regionally metamorphosed under elevated temperature and pressure, commonly during mountain building. Its age depends on the source terrane and may range from Precambrian to younger Paleozoic or Mesozoic rocks.

Uses & applications

Used locally as decorative stone, landscaping material, and occasionally building stone; attractive pieces are collected, but it is not generally a gemstone.

Geological facts

Biotite flakes split into flexible sheets and commonly produce the glittering appearance. Foliation reflects mineral alignment during metamorphism.

Field identification & locations

Look for layered or wavy foliation, abundant black/brown reflective flakes, and a tendency to split along mica-rich planes; quartz-rich streaks may resist splitting. Common in metamorphic mountain belts worldwide.