metamorphic

Biotite mica schist (probable)

Mica schist, dominated by biotite mica with quartz and feldspar; possible pyrite or other sulfides

AI-generated identification · may be incorrect

Dark gray to black, strongly foliated and sparkly, with platy mica flakes and granular quartz/feldspar. Hardness is typically 2.5–3 for exposed biotite and 6–7 for quartz; vitreous to pearly luster, with mica’s perfect basal cleavage and schistose texture.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or a clay-rich sediment was subjected to regional metamorphism, typically during mountain building. Its exact geological age cannot be determined from the image; schists range from Precambrian to modern tectonic belts.

Uses & applications

Used locally as decorative stone, landscaping aggregate, and occasionally dimension stone, though its foliation makes it prone to splitting. Attractive mica-rich specimens are collected but are generally low-value.

Geological facts

The glitter comes mainly from aligned mica flakes reflecting light; foliation records directed pressure and mineral recrystallization. A metallic yellow area could be pyrite, but this cannot be confirmed visually.

Field identification & locations

Look for layered or wavy cleavage, abundant reflective mica, and easy splitting along foliation; a streak, hardness, and acid test can refine identification. Common in metamorphic mountain belts worldwide, including the Appalachians, Rockies, and Alps.