metamorphic

Biotite schist

Mica schist, chiefly quartz + biotite mica; approximate composition varies

AI-generated identification · may be incorrect

Typically medium- to coarse-grained, silvery gray to black, with a strong foliated texture and glittery mica luster. Biotite has Mohs hardness 2.5–3, quartz 7; mica flakes show one perfect cleavage, while the rock commonly splits along foliation.

Identified September 6, 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, with recrystallization and alignment of mica. Individual examples may range from Precambrian to much younger, depending on locality.

Uses & applications

Used mainly as decorative stone, landscaping material, and educational or collector specimens; strong, uniform varieties can be cut for wall stone, though foliation limits structural use.

Geological facts

The glitter comes from reflective biotite or muscovite flakes, and the wavy bands record directed pressure during metamorphism.

Field identification & locations

Identify it by visible aligned mica flakes, sparkly foliation, and easy splitting into platy surfaces; distinguish it from gneiss by its stronger schistosity and less distinct light-dark banding. Common in metamorphic mountain belts worldwide, including the Appalachians, Alps, and New England.