metamorphic
Gneiss
Gneiss
AI-generated identification · may be incorrectHardness of 6-7 on Mohs scale, distinct alternating light and dark compositional banding (gneissic banding), vitreous to dull luster, and granular crystal structure.
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Physical properties
Hardness of 6-7 on Mohs scale, distinct alternating light and dark compositional banding (gneissic banding), vitreous to dull luster, and granular crystal structure.
Formation & geological history
Formed through high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under intense heat and directed pressure, typically during continental collisions.
Uses & applications
Used primarily as crushed stone for construction, road aggregate, and dimension stone for building facings.
Geological facts
Gneiss contains some of the oldest known rocks on Earth, with certain samples dating back over 4 billion years. The distinct bands are caused by the segregation of light and dark minerals.
Field identification & locations
Identify by its characteristic zebra-like stripes of light minerals (quartz, feldspar) and dark minerals (biotite, amphibole). Found worldwide in ancient shield areas and mountain cores.
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