metamorphic
Likely banded metamorphic pebble (possibly gneiss)
Gneiss, composition undetermined; visual identification is tentative
AI-generated identification · may be incorrectSmall, rounded, dark gray pebble with lighter bands and a matte-to-slightly-satin surface. Gneiss commonly contains quartz and feldspar with dark biotite or hornblende; hardness is roughly 6–7 Mohs, but cannot be confirmed from the image.
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Physical properties
Small, rounded, dark gray pebble with lighter bands and a matte-to-slightly-satin surface. Gneiss commonly contains quartz and feldspar with dark biotite or hornblende; hardness is roughly 6–7 Mohs, but cannot be confirmed from the image.
Formation & geological history
Gneiss forms when existing rock is recrystallized under high heat and pressure; its age depends on the source rock and cannot be determined visually. The bands may reflect mineral segregation during metamorphism.
Uses & applications
A pebble of this size is mainly a collector or decorative specimen; gneiss is also used as dimension stone and aggregate.
Geological facts
The alternating light and dark bands are called gneissic banding, though stripes alone cannot distinguish gneiss from other banded rocks.
Field identification & locations
Found commonly in glacial deposits and stream gravels, including the Pacific Northwest. Check for interlocking mineral grains and irregular, crystalline bands; the photo is too small to confirm composition or texture.
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