metamorphic
Banded gneiss pebble
Gneiss, typically quartz–feldspar–mica assemblage
AI-generated identification · may be incorrectHardness about 6–7 Mohs; rounded, tan to gray-brown with distinct fine compositional banding and silky-to-dull luster. The layering reflects alternating quartz/feldspar-rich and mica-rich bands; cleavage is weak or absent overall, though mica may split.
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Physical properties
Hardness about 6–7 Mohs; rounded, tan to gray-brown with distinct fine compositional banding and silky-to-dull luster. The layering reflects alternating quartz/feldspar-rich and mica-rich bands; cleavage is weak or absent overall, though mica may split.
Formation & geological history
Formed when preexisting igneous or sedimentary rock underwent high-grade metamorphism, commonly during Precambrian to Paleozoic mountain-building. Its smooth shape is from erosion and transport in a stream, beach, or glacial deposit.
Uses & applications
Primarily a teaching, landscaping, and decorative stone; attractive slabs may be used for countertops or facing, though this small pebble has negligible commercial use.
Geological facts
Gneissic banding is produced by mineral segregation and deformation under intense heat and pressure, not ordinary sedimentary bedding.
Field identification & locations
Identify it by continuous light-dark mineral bands, granular texture, and resistance to scratching by a steel tool; quartz-rich areas may scratch glass. Common in glaciated terrains and ancient continental shields worldwide.
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