metamorphic
Gneiss
Gneiss
Hardness of 6-7 on the Mohs scale, characterized by distinct alternating light and dark compositional banding (gneissic banding), vitreous to dull luster, granular crystal structure, specific gravity around 2.6-2.9.
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Physical properties
Hardness of 6-7 on the Mohs scale, characterized by distinct alternating light and dark compositional banding (gneissic banding), vitreous to dull luster, granular crystal structure, specific gravity around 2.6-2.9.
Formation & geological history
Formed by high-grade regional metamorphism, typically originating from igneous rocks like granite or sedimentary rocks like shale, subjected to intense heat and directed pressure deep within the Earth's crust.
Uses & applications
Used primarily as crushed stone for road construction, building facades, landscaping, and occasionally as dimension stone for countertops and architectural tiles.
Geological facts
Gneiss includes some of the oldest rocks found on Earth, with certain formations dating back over 4 billion years, such as the Acasta Gneiss in Canada.
Field identification & locations
Easily identified by its characteristic zebra-like striping or banding of light and dark minerals; commonly found in ancient shield areas and deeply eroded mountain belts.
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