metamorphic

Banded gneiss pebble

Gneiss, likely quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Typically Mohs 6–7; pale gray to white with dark biotite or amphibole bands, vitreous to pearly luster, granular interlocking crystals, and weak-to-absent cleavage as a whole rock. The rounded shape indicates water abrasion, likely from a river or beach.

Identified September 10, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when preexisting igneous or sedimentary rock underwent high-grade metamorphism, producing compositional banding through recrystallization and mineral segregation. Gneiss commonly formed during Precambrian to Phanerozoic mountain-building events.

Uses & applications

Used as crushed aggregate, road stone, building stone, landscaping material, and occasionally ornamental slabs. This small rounded specimen is mainly suitable for collecting or display.

Geological facts

The dark streaks are likely mica or amphibole-rich layers, while the light portions contain quartz and feldspar. Its banding distinguishes gneiss from more uniformly textured granite, though a precise identification requires a fresh surface or mineral testing.

Field identification & locations

Common in exposed continental mountain belts and glacial or stream gravels, including Scandinavia, Canada, the northeastern United States, and the Alps. Look for alternating light and dark mineral bands and test hardness against glass; a definitive identification may require a hand lens or thin section.