metamorphic

Banded metamorphic pebble, likely gneiss

Foliated gneiss; quartz–feldspar–mica assemblage

AI-generated identification · may be incorrect

Gray-green, strongly banded and foliated, with a dull to slightly sparkly luster; likely Mohs hardness 6–7, no obvious cleavage in the whole pebble, and moderate-to-high specific gravity (~2.6–2.8). The image is somewhat out of focus, so mineral identification is approximate.

Identified September 17, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when preexisting igneous or sedimentary rock underwent high-grade heat and pressure, segregating minerals into light and dark bands; commonly Precambrian to younger. It appears water-worn from a stream or beach gravel deposit.

Uses & applications

Used as crushed stone, aggregate, dimension stone, and decorative landscaping material; attractive pieces may be collected but are generally low-value.

Geological facts

The alternating bands reflect mineral separation during metamorphism rather than simple layering. Dark bands may contain biotite or amphibole, while pale bands are commonly quartz and feldspar.

Field identification & locations

Identify it by hard, irregularly alternating light/dark bands and planar foliation; a glassy quartz-rich streak and mica sparkle support gneiss. Common in glaciated terrains, mountain belts, and river gravels worldwide.