metamorphic
Banded gneiss (probable)
Gneiss, commonly quartz–feldspar–mica bearing
AI-generated identification · may be incorrectA coarse, banded metamorphic rock with dark mica/amphibole-rich layers and pale quartz/feldspar; typically Mohs 6–7, vitreous to pearly luster, granular texture, and no prominent cleavage as a whole. The rounded, polished surface obscures diagnostic grains.
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Physical properties
A coarse, banded metamorphic rock with dark mica/amphibole-rich layers and pale quartz/feldspar; typically Mohs 6–7, vitreous to pearly luster, granular texture, and no prominent cleavage as a whole. The rounded, polished surface obscures diagnostic grains.
Formation & geological history
Formed by high-grade regional metamorphism of granite or sedimentary protoliths, producing mineral segregation and foliation; commonly Precambrian to younger. Exact age and composition require a fresh, unpolished surface or laboratory testing.
Uses & applications
Used as dimension stone, building aggregate, paving, landscaping rock, and occasionally decorative slabs; generally not a gemstone.
Geological facts
The dark-and-light banding reflects recrystallization and tectonic deformation rather than ordinary layering. It can resemble banded granite, schist, or migmatite in photographs.
Field identification & locations
Look for alternating light quartz/feldspar and dark mica/amphibole bands, aligned minerals, and a hard, crystalline texture; common in ancient continental shields and metamorphic mountain belts. The specimen may also be a polished banded granite or schist, so visual identification is provisional.
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