metamorphic

Gneiss (likely banded granitic gneiss)

Quartz–feldspar–mica gneiss; commonly containing biotite and/or amphibole

AI-generated identification · may be incorrect

Coarse-grained, foliated rock with pale gray-white quartz and feldspar, dark biotite/amphibole bands, and possible pink potassium feldspar. Hardness is about 6–7 Mohs; luster is generally vitreous to pearly, with weak cleavage in quartz and feldspar and strong foliation overall.

Identified September 2, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed when granite or another felsic rock undergoes high-pressure, high-temperature regional metamorphism, producing compositional banding and recrystallization. Typical ages range from Precambrian to younger mountain-building events.

Uses & applications

Used as dimension stone, decorative landscaping stone, aggregate, and occasionally countertops or architectural slabs; ordinary hand specimens have modest collector value.

Geological facts

The specimen’s irregular dark-and-light banding, coarse texture, and pale mineral-rich patches are consistent with gneiss, though a photograph cannot distinguish it confidently from migmatite or strongly foliated granite.

Field identification & locations

Common in ancient continental shields and mountain belts, including Canada, Scandinavia, the United States, India, and Australia. Look for alternating mineral bands, interlocking grains, and resistance to scratching by a steel knife; a fresh surface is more diagnostic than weathered surfaces.