metamorphic

Banded gneiss

Gneiss, typically quartz–feldspar–mica ± amphibole

AI-generated identification · may be incorrect

Usually medium- to coarse-grained, with alternating light quartz/feldspar bands and darker biotite or amphibole layers; Mohs hardness about 6–7, vitreous to pearly luster, no consistent cleavage as a whole, and specific gravity roughly 2.6–2.8.

Identified September 6, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed by high-grade metamorphism of granite, sedimentary rocks, or volcanic protoliths, commonly during Precambrian to Paleozoic mountain-building; intense heat and pressure segregate minerals into compositional bands.

Uses & applications

Used as crushed aggregate, dimension stone, paving, and occasionally architectural slabs; attractive polished pieces may be collected, but it is rarely a gemstone.

Geological facts

The image shows strongly foliated, weathered banding with folded or streaked mineral layers, characteristic of gneiss rather than an even-grained granite.

Field identification & locations

Identify it by alternating light and dark mineral bands, coarse grains, and foliation; common in ancient continental shields and metamorphic mountain belts worldwide. Exact classification requires a fresh surface or thin section.