metamorphic
Polished banded gneiss
Gneiss, typically quartz–feldspar–mica assemblage
AI-generated identification · may be incorrectHardness about 6–7 Mohs; dark gray to black with white quartz/feldspar bands, vitreous to pearly luster, and strongly foliated, banded texture. It has no consistent cleavage as a whole, though mica layers may split.
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Physical properties
Hardness about 6–7 Mohs; dark gray to black with white quartz/feldspar bands, vitreous to pearly luster, and strongly foliated, banded texture. It has no consistent cleavage as a whole, though mica layers may split.
Formation & geological history
Formed when preexisting granite or sedimentary rock underwent intense heat and pressure, commonly during mountain-building; individual specimens may be hundreds of millions to over a billion years old.
Uses & applications
Used as crushed aggregate, building stone, facing slabs, landscaping stone, and decorative polished objects such as this heart. It has little gemstone value but good ornamental appeal.
Geological facts
The alternating light and dark bands reflect mineral segregation during metamorphism; folding and deformation can produce the dramatic swirls visible here.
Field identification & locations
Identify it by coarse, interlocking grains and light–dark mineral banding rather than sedimentary layers. Common in ancient continental shields and metamorphic mountain belts, including Scandinavia, Canada, India, Brazil, and the United States.
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