metamorphic

Banded gneiss pebble

Gneiss, commonly quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Hardness about 6–7 Mohs; dark gray to black with pale quartz/feldspar bands, dull to slightly vitreous luster, and irregular fracture. The foliation and alternating mineral bands reflect recrystallized, compositionally layered rock.

Identified September 5, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed by intense heat and pressure that metamorphosed granite or sedimentary protoliths, typically deep in ancient continental crust; many gneisses are Precambrian, older than 540 million years. This rounded specimen was likely shaped by stream or glacial transport.

Uses & applications

Used as crushed aggregate, dimension stone, landscaping rock, and building facing; attractive polished pieces are collected or used decoratively. This small natural pebble has modest commercial value.

Geological facts

Its light bands are chiefly quartz and feldspar, while dark bands commonly contain biotite, amphibole, or other ferromagnesian minerals. Gneissic banding is generally stronger and more irregular than the layering of slate or schist.

Field identification & locations

Identify it by coarse grains and alternating light/dark mineral bands, rather than flat cleavage; a hand lens may reveal quartz, feldspar, and mica. Common in ancient shield regions and metamorphic mountain belts worldwide.