metamorphic
Gneiss
Orthogneiss / Paragneiss
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 granular crystal structure.
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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 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 mountain-building events.
Uses & applications
Used primarily as crushed stone for road construction, building facades, landscaping, and dimension stone countertops.
Geological facts
Gneiss contains some of the oldest known rock material on Earth, with certain zircon grains dating back over 4 billion years.
Field identification & locations
Identify by its characteristic zebra-like alternating bands of light quartz/feldspar and dark biotite/amphibole minerals. Found globally in ancient shield areas and core mountain ranges.
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