metamorphic

Coarse-grained metamorphic rock, likely gneiss

Biotite–quartz–feldspar gneiss (tentative; exact identification requires testing)

AI-generated identification · may be incorrect

Gray to brown, foliated and strongly crystalline, with visible pale quartz/feldspar and dark biotite-like minerals; vitreous to pearly luster. Typical hardness is about 6–7 Mohs, with weak-to-good foliation and no obvious cleavage on the specimen surface.

Identified September 11, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when preexisting granite or sedimentary rock underwent high-grade metamorphism, producing mineral segregation and foliation, commonly during Precambrian to Paleozoic mountain-building. The rounded shape likely reflects transport and weathering.

Uses & applications

Used as crushed stone, aggregate, road material, dimension stone, and occasionally decorative slabs; usually has little gem value.

Geological facts

Gneiss commonly shows alternating light and dark bands, though this piece is irregularly foliated and could also be weathered schist or granitic rock.

Field identification & locations

Look for planar mineral alignment or banding, abundant quartz and feldspar, and sparkly mica flakes; a streak test, acid test, and fresh broken surface would improve identification. Common worldwide in ancient continental shields and metamorphic mountain belts.