metamorphic

Gneiss

Gneiss (High-grade metamorphic rock)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs); Color: Alternating dark and light bands of gray, black, and white; Luster: Dull to vitreous; Texture: Coarse-grained with distinct foliation (gneissose banding); Gravity: 2.6-2.9.

Hardness: 6-7 (Mohs)
Color: Alternating dark and light bands of gray, black, and white
Luster: Dull to vitreous

Identified July 12, 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 through high-grade regional metamorphism of pre-existing igneous rocks (like granite) or sedimentary rocks (like shale) under extreme heat and pressure. Most gneiss is hundreds of millions to billions of years old.

Uses & applications

Used primarily as crushed stone for road construction and railroad ballast, or as dimension stone for building facades, floor tiles, and grave markers. High-quality specimens are used for countertops.

Geological facts

The Acasta Gneiss in Canada is one of the oldest known crustal rock formations on Earth, dating back approximately 4 billion years. The banding is caused by the segregation of minerals during intense pressure.

Field identification & locations

Identify by looking for 'gneissose banding'—alternating layers of light (quartz, feldspar) and dark (biotite, hornblende) minerals. Found globally in the roots of mountain ranges and ancient continental shields.