metamorphic

Biotite-rich schist

Mica schist; chiefly quartz, biotite mica, feldspar, and accessory sulfides/iron oxides

AI-generated identification · may be incorrect

Typically medium- to coarse-grained, dark gray to black, with bright bronze-gold and silvery mica flakes and a distinctly foliated, sparkly surface. Biotite hardness is about 2.5–3 Mohs; quartz is 7; mica has perfect one-direction cleavage and the rock commonly splits along foliation.

Identified September 17, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or another clay-rich sediment was subjected to elevated temperature and pressure during regional metamorphism, commonly during mountain building. Its exact age cannot be determined from the image; schists range from Precambrian to younger orogenic rocks.

Uses & applications

Used mainly as decorative facing stone, landscaping material, and mineral or lapidary specimens; strong, unfoliated varieties may be used locally as dimension stone, but foliation limits structural use.

Geological facts

The gold color is likely reflective biotite or weathered sulfide minerals rather than actual gold. A hand lens should reveal platy mica grains aligned in parallel layers.

Field identification & locations

Common in metamorphic belts worldwide, including the Appalachians, New England, the Alps, and many Precambrian shields. Identify it by its aligned mica sheen, foliation, and tendency to split into flaky slabs.