metamorphic

Banded Gneiss

Gneiss (High-grade regional metamorphic rock)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs); Color: Dark grey to brown with tan or yellowish bands; Luster: Dull to resinous (when wet); Structure: Foliated with distinct compositional banding (gneissose banding); Cleavage: Poor.

Hardness: 6-7 (Mohs)
Color: Dark grey to brown with tan or yellowish bands
Luster: Dull to resinous (when wet)

Identified July 15, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through high-grade regional metamorphism of igneous (protolith often granite or diorite) or sedimentary rocks under extreme pressure and temperature, typically during mountain-building events. Ages vary from hundreds of millions to billions of years.

Uses & applications

Used as crushed stone for road construction, decorative aggregate, building stone, and occasionally for landscaping or low-cost lapidary practice.

Geological facts

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

Field identification & locations

Identify in the field by looking for alternating light and dark mineral bands. It is extremely common in mountainous regions or glacial drift. Collectors look for high-contrast banding patterns.