metamorphic

Banded Gneiss

Gneiss (High-grade Regional Metamorphic Rock)

AI-generated identification · may be incorrect

Hardness: 6-7 (Mohs scale); Color: alternating light (quartz/feldspar) and dark bands; Luster: Vitreous to dull; Crystal Structure: Coarse-grained foliated; Cleavage: Poor, though it can split along foliation layers.

Hardness: 6-7 (Mohs scale)
Color: alternating light (quartz/feldspar) and dark bands
Luster: Vitreous to dull

Identified April 10, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under extreme heat and pressure. This specimen shows 'gneissic banding' and appears water-worn (rounded) from river or glacial activity.

Uses & applications

Commonly used as crushed stone for road construction, as architectural veneer, flooring, and decorative landscaping stones.

Geological facts

Gneiss is one of the oldest rock types found on Earth; the Acasta Gneiss in Canada is approximately 4 billion years old. The banding occurs due to the segregation of minerals during recrystallization.

Field identification & locations

Identify in the field by looking for 'schistosity' or clear compositional banding (stripes) and a coarse texture. It will not fizz with acid (unlike marble) and is very hard.