metamorphic

Gneiss

Hardness: 6-7 on Mohs scale; Color: Banded grey, white, pink, and black; Luster: Dull to vitreous; Structure: Foliated with distinct compositional banding (gneissose banding); Cleavage: Poor.

Hardness: 6-7 on Mohs scale
Color: Banded grey, white, pink, and black
Luster: Dull to vitreous

Identified July 3, 2026More metamorphic →

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Physical properties

Hardness: 6-7 on Mohs scale; Color: Banded grey, white, pink, and black; Luster: Dull to vitreous; Structure: Foliated with distinct compositional banding (gneissose banding); Cleavage: Poor.

Formation & geological history

Formed through high-grade regional metamorphism of pre-existing igneous rocks (like granite) or sedimentary rocks (like shale) under intense heat and pressure, typically during mountain-building events.

Uses & applications

Used as a dimension stone for flooring, gravestones, and facing on buildings; also crushed for use in road construction and as railroad ballast.

Geological facts

Gneiss contains some of the oldest known rocks on Earth, such as the Acasta Gneiss in Canada, which is approximately 4 billion years old.

Field identification & locations

Identify by looking for 'salty and peppered' mineral bands that are coarse-grained. Unlike schist, it does not split easily along planes. Common in the roots of mountain ranges and crystalline shields.