metamorphic

Weathered gneiss (probable)

Banded quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Typically medium-to-coarse grained, gray with pale quartz/feldspar and darker biotite or amphibole bands; minerals show weak foliation and uneven, nonconchoidal fracture. Hardness is roughly 6–7 Mohs, vitreous to dull luster, and specific gravity about 2.6–2.8.

Identified September 4, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when granite or other rocks underwent intense regional metamorphism at high temperature and pressure, commonly during Precambrian to Paleozoic mountain-building events. The specimen appears strongly weathered and rounded by transport.

Uses & applications

Used as crushed aggregate, road stone, riprap, building stone, and occasionally dimension stone; attractive polished pieces are used decoratively but are not usually gem material.

Geological facts

Gneiss commonly preserves alternating light and dark mineral bands produced by metamorphic segregation. It can resemble granite, but its streaky mineral alignment and compositional banding favor gneiss.

Field identification & locations

Look for aligned dark minerals and pale quartz-feldspar layers; a glassy quartz grain can scratch glass, while feldspar generally shows cleavage. Common in ancient continental shields and glacial or river gravels; exact identification requires a fresh broken surface or thin section.