metamorphic
Banded gneiss pebble
Gneiss, chiefly quartz–feldspar–biotite (composition variable)
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray-blue and cream compositional bands, typically dull to slightly silky, with granular interlocking crystals and no prominent cleavage. Its rounded shape indicates water abrasion and it may be a polished or naturally smoothed pebble.
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Physical properties
Hardness about 6–7 Mohs; gray-blue and cream compositional bands, typically dull to slightly silky, with granular interlocking crystals and no prominent cleavage. Its rounded shape indicates water abrasion and it may be a polished or naturally smoothed pebble.
Formation & geological history
Formed when preexisting igneous or sedimentary rock underwent intense high-grade metamorphism, causing minerals to recrystallize and segregate into bands; commonly Precambrian to Paleozoic in age. Found in metamorphic terrains and glacial or river gravels.
Uses & applications
Used as decorative stone, landscaping aggregate, and occasionally for countertops or specimen collecting; this small piece has modest commercial value.
Geological facts
The light bands are usually quartz and feldspar, while darker bands commonly contain biotite, amphibole, or other ferromagnesian minerals. Strong banding distinguishes gneiss from more uniformly textured granite.
Field identification & locations
Identify it by alternating light and dark mineral bands, granular texture, and lack of true sedimentary layering or vesicles; a streak, hardness, and close inspection with a loupe help confirm it. Common in shield regions, mountain belts, and streambeds downstream from them.
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