metamorphic

Banded gneiss

Foliated quartz–feldspar gneiss, likely biotite-bearing

AI-generated identification · may be incorrect

Pale gray-green with wavy light and dark mineral bands and a coarse, crystalline texture. Gneiss has no single hardness; quartz and feldspar are about 6–7 Mohs, with a nonmetallic luster and weak cleavage dominated by foliation.

Identified September 24, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when pre-existing igneous or sedimentary rock underwent high-grade heat and pressure, separating minerals into bands. Gneisses occur in ancient continental crust, commonly billions of years old; this specimen’s age and provenance cannot be determined from the image.

Uses & applications

Used as dimension stone, paving and landscaping material, and as a decorative facing stone; attractive pieces are collected.

Geological facts

Gneissic banding records mineral segregation during metamorphism and can resemble sedimentary layers, but the bands are crystalline rather than deposited beds.

Field identification & locations

Look for coarse, interlocking grains arranged in alternating light quartz/feldspar-rich and darker mica-rich bands; the pictured slab is consistent with gneiss, though mineral identification needs close inspection. Gneiss is widespread in ancient mountain belts and exposed Precambrian shields.