metamorphic

Biotite schist (mica-rich metamorphic rock)

Mica schist, chiefly quartz, feldspar, and biotite mica

AI-generated identification · may be incorrect

Likely medium-grained with abundant reflective, platy biotite; brown-black color, vitreous to pearly luster, and strong foliation. Hardness is about 2.5–3 for biotite and 6–7 for quartz; mica flakes show one perfect cleavage.

Identified September 6, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or another clay-rich protolith underwent regional metamorphism under elevated temperature and pressure, commonly during mountain building. Exact geological age cannot be determined from the photograph.

Uses & applications

Used locally as decorative stone, aggregate, or landscaping material, though its pronounced foliation limits structural use; attractive pieces are collected. It is generally not a jewelry gemstone.

Geological facts

The glitter is caused by aligned mica sheets reflecting light, while darker granular areas may be quartz, feldspar, or accessory minerals. Schistosity records the direction of metamorphic pressure and deformation.

Field identification & locations

Identify it by its sparkly, layered texture and flakes that can peel along foliation; a steel nail typically scratches biotite but not quartz. Common worldwide in metamorphic belts, including the Appalachians, Alps, and Precambrian shields.