metamorphic

Biotite schist

Mica schist, composed mainly of biotite mica and quartz with feldspar and iron oxides

AI-generated identification · may be incorrect

Typically medium- to coarse-grained, dark brown to black and silvery, with a glittering micaceous luster and pronounced foliation; mica has Mohs hardness 2–3, quartz about 7. Crystals are platy, and mica shows perfect basal cleavage.

Identified September 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or other clay-rich sedimentary rock underwent regional metamorphism, commonly during mountain building; its exact geological age cannot be determined from the image. Orange-brown areas likely represent weathered iron-bearing minerals.

Uses & applications

Used mainly as a decorative stone, teaching specimen, and collector material; strongly foliated pieces have limited construction value because they split readily.

Geological facts

The sparkling flakes are reflective biotite rather than metallic metal. Schistosity develops as mica grains recrystallize and align under directed pressure and heat.

Field identification & locations

Identify it by abundant visible, flaky mica, glittery foliation, and easy splitting along aligned layers; common in metamorphic mountain belts worldwide, including the Appalachians, New England, Scotland, and the Alps.