metamorphic

Banded gneiss pebble

Gneiss, likely quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Fine-to-medium-grained, rounded and strongly foliated, with pale gray-green mineral bands; typically Mohs 6–7, vitreous to dull luster, no prominent cleavage as a whole, and specific gravity about 2.6–2.8. The elongated grooves and parallel texture may reflect weathered foliation or striated metamorphic fabric.

Identified September 18, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when granite or other felsic rock underwent high-temperature, high-pressure metamorphism, commonly during Precambrian to Paleozoic mountain building; the specimen was later rounded by stream or coastal transport.

Uses & applications

Gneiss is used as dimension stone, paving, aggregate, and landscaping rock; attractive polished varieties are used decoratively, but this weathered pebble has little commercial value.

Geological facts

Gneiss commonly contains quartz, potassium feldspar, plagioclase, biotite, and amphibole. Its alternating mineral bands record compositional segregation during metamorphism.

Field identification & locations

Identify it by hardness, visible foliation or banding, granular texture, and resistance to scratching by steel; unlike slate, it lacks a uniformly planar cleavage. Common in glaciated terrains, mountain belts, and river gravels worldwide.