metamorphic
Banded gneiss fragment
Gneiss, likely quartz–feldspar–mica gneiss
AI-generated identification · may be incorrectLight gray, white, and dark mineral bands with a granular crystalline texture; typically quartz, feldspar, and biotite/hornblende. Hardness is about 6–7 Mohs, with vitreous to pearly luster and weak-to-no cleavage as a whole rock.
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Physical properties
Light gray, white, and dark mineral bands with a granular crystalline texture; typically quartz, feldspar, and biotite/hornblende. Hardness is about 6–7 Mohs, with vitreous to pearly luster and weak-to-no cleavage as a whole rock.
Formation & geological history
Formed when granite or other felsic rock underwent intense heat and pressure, causing mineral recrystallization and compositional banding. Its exact age cannot be determined from the photograph; gneiss commonly ranges from Precambrian to younger metamorphic terrains.
Uses & applications
Used as crushed aggregate, road stone, building stone, countertops, monuments, and landscaping material; attractive banded pieces are collected but usually have modest value.
Geological facts
The dark stripe is likely mica- or amphibole-rich material, while the pale portions are quartz and feldspar. Gneissic banding reflects metamorphic segregation and deformation rather than ordinary sedimentary layering.
Field identification & locations
Identify it by alternating light/dark crystalline bands, visible interlocking grains, and a hard, non-foliated-to-foliated texture; it is commonly found in mountain belts and glacial gravels. The image may also show banded granite, so laboratory testing would be needed for certainty.
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