metamorphic
Banded gneiss
Foliated silicate rock, typically quartz–feldspar–mica gneiss
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray-green and brown, with strong alternating light and dark bands, glassy to dull luster, granular crystals, and weak-to-moderate foliation rather than true cleavage. Likely contains quartz, feldspar, biotite or amphibole, and possibly chlorite or epidote.
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
Hardness about 6–7 Mohs; gray-green and brown, with strong alternating light and dark bands, glassy to dull luster, granular crystals, and weak-to-moderate foliation rather than true cleavage. Likely contains quartz, feldspar, biotite or amphibole, and possibly chlorite or epidote.
Formation & geological history
Formed when preexisting igneous or sedimentary rock underwent high-grade regional metamorphism, causing mineral segregation and banding; individual specimens may range from Precambrian to younger geological ages.
Uses & applications
Used as dimension stone, landscaping rock, aggregate, and architectural facing; attractive polished pieces are collected, though this rough specimen has modest commercial value.
Geological facts
Gneissic banding records intense heat, pressure, and deformation deep in the continental crust and commonly indicates amphibolite- to granulite-facies metamorphism.
Field identification & locations
Identify it by alternating mineral bands, coarse interlocking grains, and a streaky texture; common in ancient continental shields and metamorphic mountain belts. The image could also represent strongly foliated amphibolite or schist, so mineral tests would refine identification.
More like this
