metamorphic
Gneiss
Foliated metamorphic rock
AI-generated identification · may be incorrectHardness of 6-7 on Mohs scale; banded appearance with alternating light and dark mineral layers; vitreous to dull luster; specific gravity 2.6-2.9.
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Physical properties
Hardness of 6-7 on Mohs scale; banded appearance with alternating light and dark mineral layers; vitreous to dull luster; specific gravity 2.6-2.9.
Formation & geological history
Formed by high-grade regional metamorphism of pre-existing igneous or sedimentary rocks under extreme heat and pressure, typically during continental collisions.
Uses & applications
Used primarily as dimension stone in construction, building facades, paving, and decorative landscaping.
Geological facts
Some gneiss formations contain some of the oldest rocks on Earth, dating back over 4 billion years.
Field identification & locations
Easily identified by its distinct alternating light and dark compositional banding known as gneissic banding; common in old cratons and mountain belts.
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