metamorphic

Biotite schist (probable)

Mica schist, chiefly quartz + biotite mica; composition is visually provisional

AI-generated identification · may be incorrect

Dark gray, strongly foliated and sparkly, with platy mica grains and a granular texture; hardness about 2.5–3 for biotite and 6–7 for quartz, vitreous to pearly luster, with mica cleavage and no obvious crystal faces.

Identified September 13, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or other clay-rich sediment was regionally metamorphosed under elevated temperature and pressure, producing aligned mica foliation; commonly Paleozoic or Precambrian, depending on locality.

Uses & applications

Used locally as decorative stone, landscaping material, and occasionally wall or flooring stone; attractive mica-rich specimens are mainly collector items.

Geological facts

The glitter comes from reflected light on aligned biotite flakes. Its foliation allows splitting along planar surfaces and records the direction of metamorphic compression.

Field identification & locations

Common in regional metamorphic belts, including the Appalachians, New England, Colorado, and many Precambrian terrains. Identify it by visible aligned flakes, foliation, and sparkly dark layers; a hand lens or thin-section test can distinguish it from gneiss or slate.