metamorphic
Granitic Gneiss
Gneiss (Granite-derived)
Hardness of 6-7 on the Mohs scale; displays a distinct banded or foliated texture with alternating light bands of quartz and feldspar and dark bands of biotite or amphibole; granular and interlocking crystal structure; sub-vitreous to dull luster.
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Physical properties
Hardness of 6-7 on the Mohs scale; displays a distinct banded or foliated texture with alternating light bands of quartz and feldspar and dark bands of biotite or amphibole; granular and interlocking crystal structure; sub-vitreous to dull luster.
Formation & geological history
Formed through regional metamorphism of pre-existing igneous rocks (like granite) or sedimentary rocks under extreme heat and directed pressure deep within the Earth's crust, typically during mountain-building events over hundreds of millions of years.
Uses & applications
Used as dimension stone for building facades, flooring, paving, and occasionally as decorative landscaping rock or crushed stone for aggregate.
Geological facts
Gneiss is derived from the German word 'gnist', meaning spark or rotten, and some of the oldest rocks on Earth, dating back over 4 billion years, are types of gneiss.
Field identification & locations
Easily identified in the field by its characteristic zebra-like alternating light and dark bands (gneissic banding). Found worldwide in ancient cratons, shield areas, and core complexes of major mountain ranges.
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