metamorphic

Gneiss

Gneiss (High-grade metamorphic rock)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale), Color: Gray and white bands, Luster: Vitreous/Dull, Crystal structure: Coarse-grained/Foliated (Gneissic banding), Cleavage: Poorly developed.

Identified May 17, 2026More metamorphic →

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Physical properties

Hardness: 6-7 (Mohs scale), Color: Gray and white bands, Luster: Vitreous/Dull, Crystal structure: Coarse-grained/Foliated (Gneissic banding), Cleavage: Poorly developed.

Formation & geological history

Formed by high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under extreme pressure and temperature. Typical of Precambrian shields.

Uses & applications

Used as a building stone (facing stone), crushed stone for road construction, and occasionally for high-end countertops or cemetery monuments.

Geological facts

Gneiss is among the oldest known rocks on Earth. The Acasta Gneiss in Canada is approximately 4 billion years old.

Field identification & locations

Identified by 'Gneissic banding'—distinct light and dark colored mineral layers. Found globally in the roots of mountain ranges and ancient continental shields.