metamorphic

Banded gneiss

Felsic orthogneiss/paragneiss; chiefly quartz, feldspar, mica, and accessory amphibole or garnet

AI-generated identification · may be incorrect

Typically medium–coarse grained with alternating light quartz–feldspar and dark mica/amphibole bands; Mohs hardness about 6–7, vitreous to dull luster, weak cleavage along mica-rich layers, and no consistent crystal shape.

Identified September 18, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when granite or other sedimentary/protolithic rocks undergo high-grade metamorphism, causing mineral recrystallization and compositional banding. Most examples are Precambrian to Paleozoic, though gneiss forms in many mountain belts.

Uses & applications

Used as dimension stone, paving, aggregate, and decorative landscaping rock; attractive polished pieces may be collected, but this specimen appears ordinary and unpolished.

Geological facts

The prominent foliation and contrasting light/dark bands distinguish gneiss from massive granite; irregular fractures and weathering can obscure the banding.

Field identification & locations

Common in ancient continental shields and uplifted mountain cores, including Scandinavia, Canada, the northeastern United States, India, and Australia. Confirm with a hand lens: quartz and feldspar are light, while mica/amphibole create dark foliation; it should not fizz with dilute acid.