metamorphic

Banded gneiss with amphibolite and granitic rocks

Gneiss, commonly quartz–feldspar–biotite gneiss; associated amphibolite and granite

AI-generated identification · may be incorrect

The prominent slab shows coarse, alternating pale quartz–feldspar and dark biotite/amphibole bands, with irregular foliation; hardness is about 6–7 Mohs, nonmetallic luster, and no obvious cleavage in hand-sized fragments. The surrounding rounded cobbles include dark amphibolite/basalt and light granitoid material.

Identified September 2, 2026More metamorphic →

Explore Banded gneiss with amphibolite and granitic rocks 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

Gneiss forms when pre-existing igneous or sedimentary rocks undergo high-grade metamorphism involving intense heat and pressure, commonly during mountain building; many examples are Precambrian, roughly 1–3 billion years old. The rounded stones were later transported and abraded by river or glacial action.

Uses & applications

Used as crushed stone, riprap, aggregate, building stone, and landscaping material; attractive banded pieces may be polished for decorative use. Ordinary field specimens have little commercial value.

Geological facts

The light–dark banding records mineral segregation during metamorphism and can preserve evidence of ancient continental collisions. Amphibolite-rich layers indicate a mafic volcanic or intrusive protolith.

Field identification & locations

Identify it by coarse visible grains and strong compositional banding; unlike slate, it does not split into thin sheets. Common in ancient crystalline terrains worldwide, including Canada, Scandinavia, the northeastern United States, India, and Australia.