metamorphic

Gneiss

AI-generated identification · may be incorrect

Hardness: 6-7 Mohs; Color: Gray, pink, white, and black banded; Luster: Dull to vitreous; Structure: Foliated with distinct composition banding; Cleavage: Poorly developed along bands; Specific Gravity: 2.6-2.9.

Hardness: 6-7 Mohs
Color: Gray, pink, white, and black banded
Luster: Dull to vitreous

Identified June 28, 2026More metamorphic →

Explore Gneiss in the encyclopedia →

Identify your own rocks.

Get a report just like this from any photo, free.

App Store Google Play

Physical properties

Formation & geological history

Formed by high-grade regional metamorphism of igneous (orthogneiss) or sedimentary (paragneiss) rocks under extreme heat and pressure. It is often found in the cores of mountain belts and ancient crystalline shields.

Uses & applications

Used as crushed stone for road construction and aggregate; high-quality specimens are used for countertops, floor tiles, and as ornamental building facing.

Geological facts

Gneiss is one of the oldest rocks on Earth; the Acasta Gneiss in Canada is dated to approximately 4 billion years old. The term comes from an old German word meaning 'sparkling'.

Field identification & locations

Identify by looking for 'gneissose banding', where light-colored minerals (quartz, feldspar) and dark-colored minerals (biotite, hornblende) separate into distinct layers. Found in mountainous or glaciated regions like the Alps, Appalachians, and the Canadian Shield.