metamorphic
Banded gneiss
Biotite–quartz–feldspar gneiss
AI-generated identification · may be incorrectTypically Mohs 6–7, with alternating light quartz/feldspar-rich and dark biotite/amphibole-rich bands; vitreous to pearly luster, granular crystals, and weak foliation rather than cleavage. The specimen appears polished or naturally weathered, emphasizing the banding.
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Physical properties
Typically Mohs 6–7, with alternating light quartz/feldspar-rich and dark biotite/amphibole-rich bands; vitreous to pearly luster, granular crystals, and weak foliation rather than cleavage. The specimen appears polished or naturally weathered, emphasizing the banding.
Formation & geological history
Formed when pre-existing granite or sedimentary rock underwent intense regional metamorphism, commonly during Precambrian mountain-building events; exact age and locality cannot be determined from the image.
Uses & applications
Used as dimension stone, tiles, countertops, architectural facing, landscaping stone, and decorative or lapidary material.
Geological facts
The irregular dark-and-light compositional banding is characteristic of gneissic segregation, produced by recrystallization and deformation under high temperature and pressure.
Field identification & locations
Identify it by coarse interlocking grains and persistent compositional bands; unlike marble, it commonly contains dark mica and lacks a sugary calcite texture. Common worldwide in ancient continental shields and mountain belts.
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