metamorphic
Banded gneiss
Gneiss, commonly quartz–feldspar–mica gneiss
AI-generated identification · may be incorrectTypically hard (about 6–7 Mohs), with alternating light quartz/feldspar and dark biotite/amphibole bands; vitreous to pearly luster and no consistent cleavage as a whole. The specimen appears fine- to medium-grained, strongly foliated, and cut by white quartz-rich veins.
Identified More metamorphic →
Explore Banded gneiss in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Typically hard (about 6–7 Mohs), with alternating light quartz/feldspar and dark biotite/amphibole bands; vitreous to pearly luster and no consistent cleavage as a whole. The specimen appears fine- to medium-grained, strongly foliated, and cut by white quartz-rich veins.
Formation & geological history
Formed by high-grade regional metamorphism of granite or sedimentary protoliths, commonly during Precambrian to Paleozoic mountain-building events. Intense heat and pressure segregated minerals into compositional bands; the white veins likely formed from later silica-rich fluids.
Uses & applications
Used as dimension stone, paving, countertops, monuments, and landscaping material; attractive polished pieces are collected, though it is not generally a gemstone.
Geological facts
Gneissic banding records metamorphic deformation and mineral recrystallization. Unlike slate or schist, gneiss usually shows coarse mineral segregation and compositional layering rather than a uniformly spaced cleavage.
Field identification & locations
Identify it by contrasting, irregular light-dark bands, crystalline texture, and resistance to scratching by a steel nail. Common in ancient continental shields and metamorphic mountain belts, including Scandinavia, Canada, India, Brazil, and the United States.
More like this
