metamorphic

Gneiss

Metamorphic Gneiss (High-grade regional metamorphism)

AI-generated identification · may be incorrect

Hardness: 6-7 Mohs; Color: Banded grey, black, and white; Luster: Dull to slightly pearly; Crystal structure: Coarse-grained foliated; Cleavage: Poor; Specific gravity: 2.6-3.0

Hardness: 6-7 Mohs
Color: Banded grey, black, and white
Luster: Dull to slightly pearly

Identified July 14, 2026More metamorphic →

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Physical properties

Hardness: 6-7 Mohs; Color: Banded grey, black, and white; Luster: Dull to slightly pearly; Crystal structure: Coarse-grained foliated; Cleavage: Poor; Specific gravity: 2.6-3.0

Formation & geological history

Formed through high-grade regional metamorphism of igneous or sedimentary rocks under extreme pressure and temperature. The bands represent different mineral layers segregated by heat and pressure.

Uses & applications

Commonly used in construction as crushed stone for road bases, as a building stone for facades, and occasionally as ornamental landscaping stones.

Geological facts

Gneiss is some of the oldest rock on Earth, with the Acasta Gneiss in Canada dating back over 4 billion years. The distinctive 'gneissic banding' is caused by mineral segregation.

Field identification & locations

Identified by its distinctive bands of light and dark minerals (foliation) and lack of distinct cleavage compared to schist. Found globally in the cores of mountain ranges and ancient continental shields.