Gneiss

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.

Identified on: 5/17/2026

Mode: Standard