metamorphic
Banded gneiss pebble
Gneiss, a foliated metamorphic rock; exact mineral composition cannot be determined from the image
AI-generated identification · may be incorrectGray-green and cream wavy bands with a dull, weathered surface; likely quartz and feldspar with dark mica or amphibole. Individual mineral hardness varies, commonly about 6–7 Mohs for quartz and feldspar; gneiss has no single crystal structure or cleavage.
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Physical properties
Gray-green and cream wavy bands with a dull, weathered surface; likely quartz and feldspar with dark mica or amphibole. Individual mineral hardness varies, commonly about 6–7 Mohs for quartz and feldspar; gneiss has no single crystal structure or cleavage.
Formation & geological history
Formed when pre-existing rock was recrystallized and compositionally segregated under high heat and pressure deep in the crust. Gneiss can be of many geological ages; the pebble itself gives no age indication.
Uses & applications
Gneiss is used as crushed stone, building and landscaping stone, and occasionally as decorative dimension stone; this rounded pebble is mainly a collecting specimen.
Geological facts
The alternating light and dark bands are gneissic foliation, produced by mineral separation during metamorphism.
Field identification & locations
Look for persistent, wavy light-and-dark mineral bands rather than sedimentary layers; the rounded shape indicates transport by water or glacial action. Gneiss is widespread in ancient continental shield regions and mountain belts.
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