metamorphic
Tumbled banded gneiss
Gneiss, a foliated metamorphic rock; exact mineral composition cannot be determined from the image
AI-generated identification · may be incorrectGray-brown with dark, roughly parallel mineral bands and a fine-to-medium-grained appearance; likely quartz and feldspar with biotite or other dark minerals. Hardness is commonly about 6–7 Mohs; crystals are interlocking, with no consistent cleavage as a whole rock.
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Physical properties
Gray-brown with dark, roughly parallel mineral bands and a fine-to-medium-grained appearance; likely quartz and feldspar with biotite or other dark minerals. Hardness is commonly about 6–7 Mohs; crystals are interlocking, with no consistent cleavage as a whole rock.
Formation & geological history
Formed when pre-existing rock underwent intense heat and pressure, separating minerals into bands; many gneisses are Precambrian, though the specimen’s age is unknown.
Uses & applications
Used as decorative stone, landscaping material, and sometimes building stone; this small polished pebble is mainly for collecting or display.
Geological facts
Gneissic banding is produced by mineral segregation during metamorphism and is not sedimentary layering.
Field identification & locations
Look for alternating light and dark mineral bands and a hard, crystalline texture; gneiss occurs widely in ancient continental crust worldwide. A single pebble cannot be reliably identified to source from appearance alone.
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