metamorphic
Mica-rich metamorphic rock fragments
Biotite schist / mica schist (predominantly biotite, muscovite, and quartz)
AI-generated identification · may be incorrectDark brown-black, platy flakes with a vitreous to pearly luster and prominent basal cleavage; mica hardness is about 2.5–3 Mohs, while associated quartz is 7. Flexible or brittle thin sheets and sparkling cleavage surfaces are diagnostic.
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Physical properties
Dark brown-black, platy flakes with a vitreous to pearly luster and prominent basal cleavage; mica hardness is about 2.5–3 Mohs, while associated quartz is 7. Flexible or brittle thin sheets and sparkling cleavage surfaces are diagnostic.
Formation & geological history
Formed when clay-rich sedimentary rock undergoes regional metamorphism, aligning mica minerals into foliation; typically produced during mountain-building, commonly Paleozoic to Precambrian in age.
Uses & applications
Used locally as decorative stone, aggregate, and a source of mica; attractive pieces may be collected, though this material is generally not gem-grade.
Geological facts
The glitter comes from light reflecting off countless mica cleavage planes. Biotite is iron- and magnesium-rich and weathers relatively easily to rusty brown material.
Field identification & locations
Common in metamorphic belts worldwide, including the Appalachians, Canadian Shield, Scandinavia, and India. Identify it by abundant peelable or splintery mica sheets, foliation, and dark glitter; a hand lens can distinguish mica from metallic ore.
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