metamorphic
Banded gneiss pebble
Foliated gneiss, likely quartz–feldspar–biotite gneiss
AI-generated identification · may be incorrectDark gray to black with pale, wavy mineral bands and a dull to slightly lustrous surface. Gneiss typically has Mohs hardness around 6–7; its minerals form coarse, aligned bands rather than a regular crystal structure, with no prominent cleavage.
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Physical properties
Dark gray to black with pale, wavy mineral bands and a dull to slightly lustrous surface. Gneiss typically has Mohs hardness around 6–7; its minerals form coarse, aligned bands rather than a regular crystal structure, with no prominent cleavage.
Formation & geological history
Formed when pre-existing rock was recrystallized and segregated into light and dark bands under high heat and pressure. Gneisses occur across a wide range of geological ages, often in ancient continental crust.
Uses & applications
Commonly used as decorative stone, aggregate, and landscaping material; small polished pebbles are mainly collected or used as décor.
Geological facts
The light bands are commonly quartz and feldspar, while dark bands may contain biotite or amphibole.
Field identification & locations
Look for alternating light and dark, roughly parallel bands; the rounded shape suggests transport by water or glacial ice. Gneiss is widespread in old continental shields and mountain belts.
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