metamorphic

Gneiss

Quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Coarse-grained, gray, and weakly banded with a sparkling surface; typically quartz, feldspar, and biotite or other dark mica. Hardness is about 6–7 Mohs; crystals are mostly interlocking, with no prominent cleavage in the whole rock.

Identified October 5, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when pre-existing igneous or sedimentary rock underwent high-grade heat and pressure, producing mineral segregation and foliation. Gneisses occur in ancient continental crust, often billions of years old.

Uses & applications

Used as dimension stone, paving and construction aggregate, and decorative stone; attractive pieces may be collected.

Geological facts

Gneiss is identified by coarse interlocking minerals and compositional banding, though some specimens have subtle or irregular banding.

Field identification & locations

Common in ancient continental shields and mountain belts worldwide. The specimen’s gray, glittering texture is consistent with gneiss, but its exact mineralogy cannot be confirmed from the image alone.