metamorphic
Gneiss
Metamorphic Gneiss
AI-generated identification · may be incorrectHardness of 6-7 on the Mohs scale, exhibits distinct alternating light and dark compositional banding (gneissic banding), vitreous to dull luster, and is composed mainly of quartz, feldspar, and micas.
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Physical properties
Hardness of 6-7 on the Mohs scale, exhibits distinct alternating light and dark compositional banding (gneissic banding), vitreous to dull luster, and is composed mainly of quartz, feldspar, and micas.
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing igneous or sedimentary rocks deep within the Earth's crust under intense heat and directional pressure, often dating back billions of years.
Uses & applications
Used primarily in the construction industry as crushed stone for road bases, building facades, and dimension stone for landscaping or monuments.
Geological facts
Gneiss contains some of the oldest known rocks on Earth, such as the Acasta Gneiss in Canada, which dates back over 4 billion years.
Field identification & locations
Easily identifiable in the field by its characteristic zebra-like striping of light quartz/feldspar and dark biotite/amphibole bands; commonly found in ancient shield areas and mountain cores.
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