metamorphic
Banded gneiss
Gneiss; typically quartz–feldspar–mica assemblage
AI-generated identification · may be incorrectCoarse-grained, strongly banded rock with white quartz/feldspar layers and dark biotite- or amphibole-rich bands; minerals are interlocking with little obvious cleavage. Hardness is approximately 6–7 Mohs, with vitreous to pearly luster and high durability.
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
Coarse-grained, strongly banded rock with white quartz/feldspar layers and dark biotite- or amphibole-rich bands; minerals are interlocking with little obvious cleavage. Hardness is approximately 6–7 Mohs, with vitreous to pearly luster and high durability.
Formation & geological history
Formed by high-grade regional metamorphism that segregated minerals into compositional bands, commonly from granite or shale protoliths. Many gneisses are Precambrian, though their exact age depends on locality.
Uses & applications
Used as building stone, paving, aggregate, and decorative dimension stone; attractive polished pieces are collected but are generally low-value.
Geological facts
The alternating light and dark bands record deformation and partial recrystallization deep in the crust. It can resemble banded granite, but gneiss typically shows more pronounced mineral alignment and compositional layering.
Field identification & locations
Identify it by coarse grains and irregular light-dark banding rather than sedimentary bedding; quartz scratches glass, while feldspar and mica are visible in the bands. Common in ancient continental shields and metamorphic mountain belts.
More like this
