metamorphic

Banded gneiss pebble

Gneiss, chiefly quartz–feldspar–mica; exact variety indeterminate from image

AI-generated identification · may be incorrect

Dark gray, rounded and polished, with pale quartz/feldspar-rich bands and rusty iron-oxide staining. Typical hardness is about 6–7 Mohs, vitreous to dull luster, granular interlocking crystals, and no prominent cleavage as a whole rock.

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; commonly Precambrian to younger. The rounded shape indicates abrasion in a river, beach, or glacial deposit, followed by natural or deliberate polishing.

Uses & applications

Used as decorative stone, landscaping aggregate, countertops, and architectural facing; attractive banded pieces are collected as polished pebbles.

Geological facts

Gneissic banding records mineral segregation during intense heat and pressure, commonly deep within continental crust. Rust-colored streaks generally represent oxidation of iron-bearing minerals such as biotite or magnetite.

Field identification & locations

Identify it by alternating light and dark mineral bands, coarse crystalline texture, and resistance to scratching; distinguish it from banded slate or schist by its massive, non-fissile character. Common in ancient continental shields and glacial or river gravels.