metamorphic

Likely biotite-rich schist

Mica schist, chiefly quartz–biotite ± feldspar; exact identification requires testing

AI-generated identification · may be incorrect

Dark gray-brown, flaky/platy texture with visible mica sheen and foliation; mica hardness is about 2.5–3, while quartz is 7. Crystals are typically monoclinic mica sheets with perfect basal cleavage; density commonly 2.7–3.0.

Identified September 10, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when clay-rich sedimentary rock underwent regional metamorphism, producing aligned mica and recrystallized quartz. Usually Paleozoic or younger, though age depends on locality.

Uses & applications

Used locally as decorative stone, landscaping material, and aggregate, but its pronounced foliation limits structural construction use. Attractive pieces may be sold as educational or lapidary specimens.

Geological facts

The parallel layers reflect directed pressure and can split into thin slabs. A glassy or pearly flash from flexible dark sheets strongly supports biotite rather than ordinary shale.

Field identification & locations

Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, Himalaya, and Precambrian shields. Confirm with a streak, hardness, and close inspection for elastic mica flakes; the photo alone cannot exclude weathered gneiss or amphibolite.