metamorphic

Biotite schist

Mica schist, chiefly quartz–feldspar–biotite

AI-generated identification · may be incorrect

Medium- to coarse-grained, silvery gray and brown-black, with glittering platy mica and weak foliation; quartz and feldspar are harder than glass (Mohs 6–7), while biotite is about 2.5–3. It has a crystalline texture, mica’s perfect basal cleavage, and typical specific gravity around 2.7–2.9.

Identified September 14, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or other clay-rich sediment was subjected to regional metamorphism, causing recrystallization and alignment of mica; commonly Paleozoic or Precambrian, though age depends on locality.

Uses & applications

Used locally as decorative stone, landscaping material, and crushed aggregate; attractive pieces are collected, but it is generally unsuitable for high-wear construction because foliation promotes splitting.

Geological facts

The specimen’s glitter and planar fabric strongly suggest mica schist, though a photo cannot exclude phyllite or micaceous gneiss. Biotite commonly produces the dark bronze-black flakes, while quartz contributes the lighter granular areas.

Field identification & locations

Look for visible aligned mica flakes, sparkly cleavage surfaces, and easy splitting along foliation; a steel nail usually scratches mica but not quartz. Common in regional metamorphic belts worldwide, including the Appalachians, New England, Scandinavia, and the Himalayas.