metamorphic
Banded gneiss pebble
Gneiss, likely quartz–feldspar–mica gneiss
AI-generated identification · may be incorrectHardness about 6–7 Mohs; gray, white, and dark mineral bands with a dull to slightly sparkling luster. The visible foliation and alternating layers reflect recrystallized quartz, feldspar, and mica; cleavage is weak overall, though mica layers split easily.
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Physical properties
Hardness about 6–7 Mohs; gray, white, and dark mineral bands with a dull to slightly sparkling luster. The visible foliation and alternating layers reflect recrystallized quartz, feldspar, and mica; cleavage is weak overall, though mica layers split easily.
Formation & geological history
Formed when preexisting igneous or sedimentary rock underwent intense heat and pressure, producing mineral segregation and banding during regional metamorphism. Gneiss commonly forms in Precambrian continental crust, though it can occur at many geological ages.
Uses & applications
Used as crushed stone, aggregate, dimension stone, landscaping rock, and occasionally decorative slabs. This small rounded piece has mainly educational or modest collecting value.
Geological facts
The banding is metamorphic foliation, not ordinary sedimentary layering. Rounded edges indicate transport and abrasion in a stream, beach, or glacial environment.
Field identification & locations
Identify it by alternating light and dark bands, granular texture, and scattered reflective mica flakes; it is commonly found in glaciated terrains and areas exposing ancient metamorphic basement, such as Canada, Scandinavia, and the northern United States.
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