metamorphic

Biotite-bearing schist

Mica schist, chiefly quartz–feldspar–biotite (phyllosilicate-rich)

AI-generated identification · may be incorrect

Typically gray to brown-black with abundant glittering mica flakes and pale quartz/feldspar patches; foliated, with platy cleavage and a micaceous luster. Hardness is about 2.5–3 for biotite and 6–7 for quartz; specific gravity 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 or volcanic protolith was regionally metamorphosed under directed pressure, producing aligned mica foliation. It commonly formed during Precambrian to Phanerozoic mountain-building events.

Uses & applications

Used locally as decorative facing stone, landscaping rock, and aggregate, though strong foliation limits structural construction use; attractive specimens are collected for their sparkle and texture.

Geological facts

The reflective flakes are likely biotite or muscovite mica, while white grains are quartz and/or feldspar. Its schistosity records the direction of ancient tectonic compression.

Field identification & locations

Identify it by visible aligned mica flakes, easy splitting along foliation, and a sparkly surface; common in metamorphic mountain belts worldwide, including the Appalachians, Alps, and Canadian Shield.