metamorphic

Banded gneiss

Foliated felsic gneiss, likely biotite–quartz–feldspar gneiss

AI-generated identification · may be incorrect

Typically Mohs 6–7, with dark gray to black and lighter gray/white mineral bands, vitreous to pearly luster, and strongly developed compositional foliation. Quartz and feldspar lack cleavage; mica-rich layers may split along foliation.

Identified September 12, 2026More metamorphic →

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Physical properties

Formation & geological history

Formed by high-grade regional metamorphism of granite or other felsic protoliths, commonly during Precambrian continental crust formation and later mountain-building events. The streaking reflects mineral segregation and deformation under intense heat and pressure.

Uses & applications

Used as dimension stone, facing and paving stone, aggregate, and landscaping material; attractive polished pieces are collected decoratively but are generally not gemstone-grade.

Geological facts

The specimen’s elongated, strongly aligned dark and light bands are characteristic of gneissic texture, distinguishing it from massive granite and finer-grained schist.

Field identification & locations

Common in ancient shield terrains and metamorphic mountain belts worldwide, including Canada, Scandinavia, India, Brazil, and the United States. Confirm with a glass-scratch test and visible quartz/feldspar grains; exact identification requires petrographic examination.