metamorphic
Gneiss
Gneiss
AI-generated identification · may be incorrectHardness 6-7 on the Mohs scale, characterized by distinct alternating light and dark compositional banding. Displays a granular structure with vitreous luster and poor cleavage.
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Physical properties
Hardness 6-7 on the Mohs scale, characterized by distinct alternating light and dark compositional banding. Displays a granular structure with vitreous luster and poor cleavage.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and directional pressure, typically Precambrian in age.
Uses & applications
Used extensively as dimensional stone in construction, building facades, flooring, and as crushed aggregate for landscaping and road paving.
Geological facts
Gneiss contains some of the oldest known geological materials on Earth, with individual zircons dated to over 4 billion years old.
Field identification & locations
Identify in the field by its prominent alternating light quartz/feldspar bands and dark biotite/hornblende bands, commonly found in ancient shield regions and mountain cores.
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