metamorphic

Banded Gneiss

Gneiss (Metamorphic Rock)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs); Color: Alternating dark and light bands (mafic and felsic); Luster: Dull to pearly; Crystal structure: Granular/Coarse; Cleavage: Poor, but exhibits foliation.

Hardness: 6-7 (Mohs)
Color: Alternating dark and light bands (mafic and felsic)
Luster: Dull to pearly

Identified June 30, 2026More metamorphic →

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Physical properties

Hardness: 6-7 (Mohs); Color: Alternating dark and light bands (mafic and felsic); Luster: Dull to pearly; Crystal structure: Granular/Coarse; Cleavage: Poor, but exhibits foliation.

Formation & geological history

Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under extreme heat and pressure. Often billions of years old (Precambrian).

Uses & applications

Used as building stone, decorative landscaping rock, crushed stone for road construction, and occasionally for high-end countertops.

Geological facts

The Acasta Gneiss in Canada is one of the oldest known crustal rocks on Earth, dated at approximately 4.03 billion years old.

Field identification & locations

Identify by distinct 'gneissic banding' where minerals are segregated into visible layers. Common in continental shields and mountain cores. Look for light bands of quartz/feldspar and dark bands of biotite/amphibole.