metamorphic

Biotite-rich schist (mica schist)

Mica schist, chiefly quartz + biotite mica, with possible feldspar

AI-generated identification · may be incorrect

Dark gray-brown, strongly sparkly and foliated, with platy mica flakes and granular quartz/feldspar; mica has perfect basal cleavage, hardness about 2.5–3, while quartz is 7. Typically has a silky to vitreous luster and variable specific gravity around 2.7–3.0.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or other clay-rich sediment was buried and regionally metamorphosed under directed pressure, producing aligned mica layers; commonly Paleozoic to Precambrian, though age depends on locality.

Uses & applications

Used locally as decorative stone, landscaping material, and occasionally building facing; attractive pieces are collected, but it is generally unsuitable for durable aggregate because foliation splits readily.

Geological facts

Its glitter comes mainly from reflected light on aligned biotite flakes, not necessarily metallic minerals. Larger pale grains may be quartz or feldspar, and the specimen could include minor garnet or sulfides.

Field identification & locations

Identify it by abundant aligned, peelable mica flakes and a pronounced layered fabric; unlike granite, it tends to split along foliation. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, and New England.