metamorphic

Biotite mica schist

Mica schist, chiefly biotite (K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂) with quartz and feldspar

AI-generated identification · may be incorrect

Dark gray-black, strongly sparkly, platy and foliated; biotite has Mohs hardness 2.5–3 and perfect basal cleavage, while quartz inclusions are harder (7). Luster is vitreous to pearly; density is typically about 2.7–3.0.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when clay-rich sedimentary rock underwent medium-grade regional metamorphism, recrystallizing into aligned mica, quartz, and feldspar. Most examples formed during ancient mountain-building events, commonly hundreds of millions to over a billion years ago.

Uses & applications

Used locally as decorative stone, aggregate, landscaping material, and occasionally thin veneer; attractive specimens are collected for their foliation and glittering mica.

Geological facts

Its glitter comes from light reflecting off thousands of cleavage surfaces rather than metallic minerals. The rock splits along mica-rich foliation planes, a key distinction from massive granite.

Field identification & locations

Identify it by abundant visible mica flakes, wavy layering, and easy splitting; common in metamorphic mountain belts worldwide, including the Appalachians, New England, Scandinavia, and the Alps. The image alone cannot confirm mineral proportions.