metamorphic

Biotite schist (probable)

Mica schist; chiefly quartz, feldspar, and biotite mica

AI-generated identification · may be incorrect

Dark gray, sparkly, and foliated with platy mica flakes; biotite has Mohs hardness 2.5–3, quartz 7, vitreous to pearly luster, and perfect mica cleavage. Specific gravity is approximately 2.7–3.0.

Identified September 6, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or other clay-rich sediment was subjected to regional metamorphism, aligning mica into foliation; commonly Paleozoic to Precambrian, though age depends on locality.

Uses & applications

Primarily a teaching and collector specimen; some schists are used locally as decorative stone, landscaping rock, or low-grade construction material, but strong foliation limits durability.

Geological facts

The glitter comes from reflective biotite surfaces, while the layered texture records directed pressure during mountain building.

Field identification & locations

Identify it by its glittering black mica, visible planar layering, and tendency to split along foliation; common in metamorphic belts worldwide, including the Appalachians, Alps, and Scandinavian mountains.