metamorphic
Banded gneiss
Gneiss, commonly quartz–feldspar–mica gneiss
AI-generated identification · may be incorrectTypically medium-grained with alternating light quartz/feldspar bands and dark biotite or amphibole; hardness about 6–7 Mohs, vitreous to dull luster, weak cleavage controlled by foliation, and specific gravity around 2.6–2.8.
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 medium-grained with alternating light quartz/feldspar bands and dark biotite or amphibole; hardness about 6–7 Mohs, vitreous to dull luster, weak cleavage controlled by foliation, and specific gravity around 2.6–2.8.
Formation & geological history
Formed when granite or other felsic rock underwent intense regional metamorphism, producing compositional banding and recrystallization; many examples formed during Precambrian to Paleozoic mountain-building events.
Uses & applications
Used locally as dimension stone, paving, landscaping rock, and aggregate; attractive polished pieces are collected, though ordinary specimens have limited commercial value.
Geological facts
The light bands are generally quartz and feldspar, while dark streaks commonly contain mica or amphibole. Its gneissic banding distinguishes it from more uniformly textured granite.
Field identification & locations
Identify it by coarse mineral grains and irregular alternating light-dark foliation; unlike sedimentary layering, the bands are metamorphic and often contorted. Common in ancient continental shields and glacially transported gravel deposits.
More like this
