metamorphic

Banded gneiss

Feldspar–quartz–mica gneiss

AI-generated identification · may be incorrect

Typically medium- to coarse-grained, with alternating pale quartz/feldspar and darker biotite or amphibole bands; Mohs hardness about 6–7, vitreous to dull luster, and weak or no cleavage as a whole. The specimen appears weathered and rounded, with foliation/banding visible across its surface.

Identified September 13, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when granite or another felsic protolith underwent intense regional metamorphism at high temperature and pressure, commonly during Precambrian mountain-building; individual ages vary widely. Common in ancient continental shields and exposed metamorphic terrains.

Uses & applications

Used as crushed aggregate, road stone, building stone, architectural slabs, and landscape rock; attractive pieces may be polished for decorative use.

Geological facts

Gneissic banding records mineral segregation and deformation during metamorphism. It can resemble banded granite, but its compositional layers are generally more strongly aligned or stretched.

Field identification & locations

Look for alternating light and dark mineral bands, interlocking grains, and a hard, durable texture; a fresh break is more diagnostic than the weathered exterior. Common worldwide, including Canada, Scandinavia, the U.S. Appalachians, and the Precambrian shield regions.