metamorphic
Banded gneiss pebble
Gneiss, typically quartz–feldspar–mica assemblage
AI-generated identification · may be incorrectHardness about 6–7 Mohs; coarse-grained, nonmetallic, with alternating pale quartz/feldspar and dark biotite or amphibole bands, plus reddish iron-oxide staining. Massive, weakly foliated, with no prominent cleavage as a whole; specific gravity about 2.6–2.8.
Identified More metamorphic →
Explore Banded gneiss pebble in the encyclopedia →Identify your own rocks.
Get a report just like this from any photo, free.
Physical properties
Hardness about 6–7 Mohs; coarse-grained, nonmetallic, with alternating pale quartz/feldspar and dark biotite or amphibole bands, plus reddish iron-oxide staining. Massive, weakly foliated, with no prominent cleavage as a whole; specific gravity about 2.6–2.8.
Formation & geological history
Formed when granite or other high-grade protolith was subjected to intense heat and pressure, causing mineral segregation into bands. Commonly Precambrian to younger, depending on the source terrane.
Uses & applications
Used as crushed stone, aggregate, dimension stone, landscaping rock, and occasionally polished decorative material; generally low jewelry value.
Geological facts
The banding is metamorphic compositional layering, not sedimentary bedding. Its rounded form indicates transport and abrasion in a river, beach, or glacial environment.
Field identification & locations
Identify by distinct light–dark mineral bands, visible interlocking grains, and resistance to scratching by a steel tool. Common in exposed continental shields and mountainous metamorphic belts.
More like this
