metamorphic

Gneiss

Gneiss (High-grade metamorphic rock)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale); Color: Banded grey, white, and black with occasional pink or tan; Luster: Dull to vitreous; Crystal Structure: Foliated (gneissic banding); Cleavage: Poorly developed along bands.

Hardness: 6-7 (Mohs scale)
Color: Banded grey, white, and black with occasional pink or tan
Luster: Dull to vitreous

Identified July 16, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through high-pressure, high-temperature metamorphism of granite or sedimentary rocks like shale. It typically forms deep within the earth's crust during mountain-building events (orogeny).

Uses & applications

Used primarily as decorative construction stone, crushed stone for road bases, flooring, and kitchen countertops due to its durability and aesthetic banding.

Geological facts

Gneiss is one of the oldest rock types found on Earth. Some of the oldest known continental crust, the Acasta Gneiss in Canada, is approximately 4 billion years old.

Field identification & locations

Identify in the field by looking for distinct mineral segregation into light and dark bands (foliation). It is extremely common in continental shields and ancient mountain ranges. Durable and heavy specimen.