metamorphic

Biotite-rich schist

Mica schist, chiefly biotite mica with quartz and feldspar

AI-generated identification · may be incorrect

Typically medium-hard (Mohs 2.5–3 for biotite; quartz-bearing specimens up to 6–7), dark brown-black with silvery reflective flakes, vitreous to pearly luster, and pronounced schistosity from aligned mica crystals. Foliation and flaky cleavage are prominent; density is commonly about 2.7–3.0.

Identified September 1, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or other clay-rich sediment is subjected to regional metamorphism during mountain building, commonly at greenschist to amphibolite-facies conditions. Its exact age cannot be determined from the image; schists range from Precambrian to young orogenic rocks.

Uses & applications

Used locally as decorative stone, landscaping material, and occasionally building stone, but strong foliation limits structural use. Attractive mica-rich pieces are collected as teaching or display specimens.

Geological facts

The glittering surfaces are reflective biotite cleavage planes, while pale grains are likely quartz or feldspar. Rust-colored patches may represent weathered iron-bearing minerals.

Field identification & locations

Identify it by visible planar foliation, easily separable mica flakes, and a sparkly dark surface; unlike slate, it has coarser, clearly visible crystals. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, and Himalaya.