metamorphic
Polished black-and-white pebble, likely gneiss
Banded gneiss; commonly composed of quartz, feldspar, and dark biotite or hornblende
AI-generated identification · may be incorrectSmooth, rounded, black-and-white banding; likely Mohs hardness 6–7, vitreous to dull luster, and interlocking crystals without obvious cleavage. The small image does not show enough detail for a definitive identification.
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Physical properties
Smooth, rounded, black-and-white banding; likely Mohs hardness 6–7, vitreous to dull luster, and interlocking crystals without obvious cleavage. The small image does not show enough detail for a definitive identification.
Formation & geological history
Gneiss forms when pre-existing rocks undergo high heat and pressure, separating minerals into light and dark bands; its age depends on its source, often hundreds of millions to billions of years.
Uses & applications
Used decoratively as a polished pebble or in landscaping and collections; gneiss is also used as dimension stone and aggregate.
Geological facts
The contrast of light quartz-feldspar and dark mica or amphibole is typical of gneissic banding.
Field identification & locations
Look for alternating mineral bands and a granular crystalline texture; rounded form suggests stream or beach transport. Gneiss occurs worldwide, including in ancient continental shields.
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