metamorphic
Banded gneiss pebble
Gneiss, commonly quartz–feldspar–mica gneiss
AI-generated identification · may be incorrectHardness about 6–7 Mohs; rounded gray pebble with alternating pale quartz/feldspar and darker mica-rich bands. Crystalline, granular texture, generally no cleavage as a whole, and a vitreous to dull luster; typical specific gravity is 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; rounded gray pebble with alternating pale quartz/feldspar and darker mica-rich bands. Crystalline, granular texture, generally no cleavage as a whole, and a vitreous to dull luster; typical specific gravity is 2.6–2.8.
Formation & geological history
Formed when pre-existing granite or sedimentary rock underwent intense high-grade metamorphism, producing compositional banding and recrystallization. The specimen’s exact age cannot be determined from the photograph; gneisses commonly range from Precambrian to younger orogenic rocks.
Uses & applications
Used as crushed aggregate, dimension stone, paving, landscaping material, and occasionally decorative architectural stone; this rounded beach pebble has mainly educational or collectible value.
Geological facts
The light bands are typically quartz and feldspar, while dark bands contain biotite, amphibole, or other ferromagnesian minerals. The visible foliation reflects mineral segregation during deep burial, heat, and directed pressure.
Field identification & locations
Identify it by alternating light and dark mineral bands, interlocking grains, and a hard, nonporous surface; unlike layered sedimentary rock, the bands are metamorphic and crystalline. Common in glaciated terrains, mountain belts, and beaches or streambeds receiving eroded continental rock.
More like this
