metamorphic

Banded gneiss pebble

Gneiss, a foliated metamorphic rock, likely quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Gray-brown, fine- to medium-grained with visible light and dark mineral bands; typically quartz, feldspar, and biotite or hornblende. Individual minerals are about Mohs 6–7 for quartz and feldspar; the pebble’s rounded shape suggests water wear, not cleavage or crystal form.

Identified September 28, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when pre-existing igneous or sedimentary rock underwent high heat and pressure, causing minerals to segregate into bands. Gneiss occurs in ancient continental crust and can be billions of years old; the specimen’s age and source cannot be determined from the image.

Uses & applications

Gneiss is used as dimension stone, paving, landscaping aggregate, and decorative stone; this small pebble is mainly suitable for collecting or display.

Geological facts

Gneissic banding records mineral separation during metamorphism and can resemble sedimentary layers, though it formed through recrystallization.

Field identification & locations

Look for alternating pale quartz/feldspar-rich and dark mica-rich bands, with a crystalline, interlocking texture. Gneiss is widespread in old mountain belts and continental shields; the image alone cannot establish its locality.