metamorphic
Gneiss
Felsic, quartz–feldspar gneiss
AI-generated identification · may be incorrectCoarse-grained, pale gray rock with visible quartz and feldspar and darker biotite or amphibole; weakly banded/foliated. Typical minerals have Mohs hardness 6–7; the whole rock has no single hardness or crystal structure.
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Physical properties
Coarse-grained, pale gray rock with visible quartz and feldspar and darker biotite or amphibole; weakly banded/foliated. Typical minerals have Mohs hardness 6–7; the whole rock has no single hardness or crystal structure.
Formation & geological history
Formed when pre-existing igneous or sedimentary rock was recrystallized under high heat and pressure, commonly deep in continental crust; its age depends on the local bedrock.
Uses & applications
Used as building and dimension stone, aggregate, and landscape stone; attractive pieces may be collected or used decoratively.
Geological facts
Gneiss is identified by mineral segregation into light and dark bands, though banding can be subtle or irregular.
Field identification & locations
The image shows a coarse, speckled, weakly foliated rock consistent with gneiss, but a photo alone cannot confirm it; similar granite or granitic schist may look alike. Gneiss occurs in ancient continental shields and mountain belts worldwide.
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