metamorphic
Gneiss
Gneiss
AI-generated identification · may be incorrectHardness 6-7 on the Mohs scale, characterized by distinct alternating light and dark compositional banding (gneissic banding). Composed mainly of quartz, feldspar, and micas.
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Physical properties
Hardness 6-7 on the Mohs scale, characterized by distinct alternating light and dark compositional banding (gneissic banding). Composed mainly of quartz, feldspar, and micas.
Formation & geological history
Formed by high-grade regional metamorphism of preexisting igneous or sedimentary rocks deep within the Earth's crust under extreme heat and pressure.
Uses & applications
Used primarily as crushed stone for construction, road aggregate, and occasionally as dimension stone for building facings and countertops.
Geological facts
Gneiss includes some of the oldest rocks on Earth, with certain formations dating back over 4 billion years. The distinct banding differentiates it from unbanded granitic rocks.
Field identification & locations
Identify by its characteristic zebra-like striping or banding of light and dark minerals. Common in ancient continental shields and mountain belts worldwide.
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