metamorphic
Polished banded gneiss
Biotite–quartz–feldspar gneiss, locally migmatitic
AI-generated identification · may be incorrectMedium- to coarse-grained, strongly banded rock with gray quartz/feldspar layers, dark biotite-rich seams, and pale pink feldspar. Mohs hardness is roughly 6–7; it has a granular texture, vitreous quartz luster, and no distinct cleavage as a whole rock.
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Physical properties
Medium- to coarse-grained, strongly banded rock with gray quartz/feldspar layers, dark biotite-rich seams, and pale pink feldspar. Mohs hardness is roughly 6–7; it has a granular texture, vitreous quartz luster, and no distinct cleavage as a whole rock.
Formation & geological history
Formed when preexisting igneous or sedimentary rock underwent high-grade metamorphism, producing mineral segregation and foliation; some pale, irregular bands may represent partial melting. Such rocks commonly formed during Precambrian to Paleozoic mountain-building events.
Uses & applications
Used as polished ornamental stone, lapidary material, countertops, tiles, and decorative objects; attractive pieces are collected as display specimens.
Geological facts
The curved light-and-dark bands record intense deformation and recrystallization deep in the continental crust. The white surface lines are likely natural quartz veins or fractures highlighted by polishing.
Field identification & locations
Identify it by alternating light felsic and dark mafic bands, visible interlocking grains, and a hard, non-porous polished surface; distinguish it from marble by its granular quartz/feldspar texture and darker biotite bands. Common in ancient continental shield regions worldwide.
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