metamorphic

Likely biotite-rich schist

Mica schist, chiefly quartz + biotite mica (approx. SiO₂ and K(Mg,Fe)₃AlSi₃O₁₀(F,OH)₂)

AI-generated identification · may be incorrect

Dark gray, strongly foliated, sparkly micaceous luster; individual flakes are commonly Mohs 2–3 with perfect basal cleavage, while quartz grains are Mohs 7. Specific gravity is roughly 2.7–3.1; the specimen appears fine- to medium-grained.

Identified September 11, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or another clay-rich sediment was regionally metamorphosed under elevated pressure and temperature, producing aligned mica layers. Commonly Paleozoic or Precambrian, though age depends on locality.

Uses & applications

Used occasionally as decorative stone, aggregate, or teaching material; attractive pieces are collected, but it is generally not a jewelry gemstone.

Geological facts

The glitter comes from reflecting mica cleavage surfaces, and the layered fabric may split into thin sheets. Dark color commonly reflects iron- and magnesium-rich biotite.

Field identification & locations

Identify by its platy, aligned flakes, glittering foliation, and easy splitting; a hand lens may reveal black/brown biotite and gray quartz. Common in regional metamorphic belts worldwide, including the Appalachians, Alps, and Canadian Shield.