metamorphic
Banded gneiss
Foliated gneiss, likely quartz–feldspar–biotite gneiss
AI-generated identification · may be incorrectDark gray to brown with alternating light and dark mineral bands and a coarse, crystalline texture. Typical minerals include quartz, feldspar, and mica; hardness is roughly 6–7 Mohs, with no consistent cleavage.
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Physical properties
Dark gray to brown with alternating light and dark mineral bands and a coarse, crystalline texture. Typical minerals include quartz, feldspar, and mica; hardness is roughly 6–7 Mohs, with no consistent cleavage.
Formation & geological history
Forms when pre-existing igneous or sedimentary rock is recrystallized under high heat and pressure, often deep in continental crust. Gneisses range widely in age, commonly including Precambrian examples.
Uses & applications
Used as dimension stone, paving and landscaping stone, aggregate, and as a collectible geological specimen.
Geological facts
The characteristic compositional banding is called gneissic foliation and reflects mineral segregation during metamorphism.
Field identification & locations
Identify it by distinct, roughly parallel light and dark bands rather than the thin splitting layers of schist. Gneiss occurs in ancient continental terrains worldwide; the small image does not establish a precise variety or locality.
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