metamorphic

Gneiss pebble

Felsic banded gneiss, likely granitic in composition

AI-generated identification · may be incorrect

Coarse-grained, gray-and-white with dark mineral streaks and weak foliation; chiefly quartz, feldspar, and biotite or hornblende. Hardness typically 6–7 Mohs; minerals have vitreous to pearly luster and gneissic banding rather than a single crystal structure.

Identified October 4, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when granite or other rock was subjected to high heat and pressure, causing minerals to recrystallize and segregate into bands. Gneisses span many geological ages; this rounded specimen’s age cannot be determined visually.

Uses & applications

Commonly used as crushed stone, building and landscaping stone, and decorative facing; this small pebble is mainly a collector or display piece.

Geological facts

The rounded shape indicates prolonged abrasion, likely in a river, beach, or glacial sediment. Gneiss is identified by its coarse mineral grains and compositional banding.

Field identification & locations

Look for alternating light quartz/feldspar and dark mica or amphibole, with streaks or bands rather than the uniform texture of granite. Gneiss is widespread in ancient continental crust and occurs in metamorphic terrains worldwide.