metamorphic

Biotite schist (probable)

Mica schist, chiefly quartz, feldspar, and biotite mica

AI-generated identification · may be incorrect

Dark brown-gray, strongly foliated and sparkly with platy mica; Mohs hardness about 2.5–3 for biotite and 6–7 for quartz. Displays micaceous cleavage, uneven granular texture, and a moderate-to-high specific gravity around 2.7–3.0.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or another clay-rich sediment was subjected to regional metamorphism, typically during mountain building; the rock may range from Precambrian to Phanerozoic in age. Heat and pressure aligned mica into visible layers.

Uses & applications

Used locally as decorative stone, landscaping material, and occasionally building stone, but its pronounced foliation limits durability. Most pieces are valued as teaching or mineral-collection specimens rather than gemstones.

Geological facts

The glitter comes from aligned biotite or possibly muscovite flakes; rusty brown areas commonly reflect oxidation of iron-bearing minerals. A definitive identification would benefit from a fresh break and close inspection of foliation.

Field identification & locations

Common in metamorphic belts worldwide, including the Appalachians, Canadian Shield, Alps, and Himalaya. Look for flakes that split into sheets and a layered fabric; streak, hardness, and thin-section examination can distinguish it from schistose gneiss.