metamorphic
Banded gneiss (probable)
Quartz–feldspar–mica gneiss; composition commonly dominated by quartz, feldspar, and biotite/hornblende
AI-generated identification · may be incorrectCoarse-grained, strongly banded, with pale quartz–feldspar layers and dark mica/amphibole streaks; typically Mohs 6–7, vitreous to dull luster, granular crystal structure, and poor/no cleavage as a whole rock. The rounded edges indicate stream or beach abrasion.
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Physical properties
Coarse-grained, strongly banded, with pale quartz–feldspar layers and dark mica/amphibole streaks; typically Mohs 6–7, vitreous to dull luster, granular crystal structure, and poor/no cleavage as a whole rock. The rounded edges indicate stream or beach abrasion.
Formation & geological history
Formed when preexisting granite or sedimentary rock underwent intense regional metamorphism at roughly 500–800°C and elevated pressure, commonly during Precambrian to Paleozoic mountain-building. Exact age cannot be determined from the photograph.
Uses & applications
Used as crushed aggregate, dimension stone, landscaping rock, and occasionally polished architectural stone; generally little jewelry value.
Geological facts
Gneissic banding records mineral segregation and deformation during metamorphism, while the light bands are likely quartz and feldspar and the dark bands mica or amphibole.
Field identification & locations
Identify it by alternating light and dark mineral bands, coarse visible grains, and a hard, massive texture; distinguish it from granite by its pronounced planar banding. Common in ancient continental shields and glacial or river deposits.
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