metamorphic

Banded gneiss

Gneiss, likely quartz–feldspar–mica gneiss

AI-generated identification · may be incorrect

Typically 6–7 Mohs; coarse-grained with alternating pale quartz/feldspar and darker mica or amphibole bands, vitreous to pearly luster, and strong foliation. The specimen appears weathered and elongated, with no visible crystal faces or cleavage-dominated texture.

Identified September 13, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when granite or other continental crustal rocks underwent intense, high-grade metamorphism involving heat and pressure, commonly during Precambrian mountain-building events. Exact age and locality cannot be determined from the photograph.

Uses & applications

Used as dimension stone, paving, aggregate, landscaping rock, and occasionally decorative facing; attractive banded pieces are collected but are generally inexpensive.

Geological facts

Gneissic banding results from mineral segregation and tectonic deformation rather than sedimentary layering. Some gneisses preserve evidence of multiple metamorphic episodes and ancient continental crust.

Field identification & locations

Identify it by coarse alternating mineral bands, pronounced foliation, and a hard, massive texture; unlike schist, it usually contains less visibly platy mica. Common in ancient shields and deeply eroded mountain belts worldwide.