metamorphic
Gneiss
Gneiss
AI-generated identification · may be incorrectHardness 6-7 on the Mohs scale, typically exhibits a banded or foliated texture with alternating light and dark mineral layers. It has a dull to vitreous luster and poor cleavage.
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Physical properties
Hardness 6-7 on the Mohs scale, typically exhibits a banded or foliated texture with alternating light and dark mineral layers. It has a dull to vitreous luster and poor cleavage.
Formation & geological history
Formed through high-grade regional metamorphism of preexisting igneous or sedimentary rocks under extreme heat and pressure, often dating back billions of years.
Uses & applications
Widely used as dimension stone for building facings, flooring, decorative landscaping, and occasionally as crushed stone for road construction.
Geological facts
Gneiss contains some of the oldest known rocks on Earth, such as the Acasta Gneiss in Canada, which is over 4 billion years old.
Field identification & locations
Easily identified in the field by its distinct alternating light-colored quartz and feldspar bands with dark biotite or amphibole layers. Found worldwide in ancient cratons and shield areas.
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