metamorphic

Foliated metamorphic rock, likely biotite gneiss or schist

Biotite-rich gneiss/schist; chiefly quartz, feldspar, and biotite mica

AI-generated identification · may be incorrect

Dark gray-black, fine- to medium-grained, with weakly visible foliation and mica-rich streaks; hardness about 5–6, vitreous to dull luster, irregular fracture, and no obvious cleavage as a whole rock.

Identified September 10, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when shale or felsic igneous rock underwent regional metamorphism under elevated temperature and pressure, commonly during mountain building; age cannot be determined from the image and may range from Precambrian to recent tectonic belts.

Uses & applications

Used as crushed aggregate, dimension stone, landscaping rock, and occasionally as decorative slabs; attractive mica foliation gives cabinet specimens modest collecting interest.

Geological facts

The elongate shape and aligned dark minerals suggest deformation and mineral alignment rather than layering from sediment deposition.

Field identification & locations

Common in metamorphic terranes worldwide, including the Appalachian Mountains, Canadian Shield, Scandinavia, and the Alps; look for planar mica alignment, alternating light quartz-feldspar bands, and glitter on a fresh surface.