metamorphic
Gneiss
Gneiss
Hardness of 6-7 on Mohs scale, typically displays distinct alternating light and dark compositional banding (gneissic banding) with quartz, feldspar, biotite, and amphibole minerals, vitreous to dull luster, foliated texture.
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Physical properties
Hardness of 6-7 on Mohs scale, typically displays distinct alternating light and dark compositional banding (gneissic banding) with quartz, feldspar, biotite, and amphibole minerals, vitreous to dull luster, foliated texture.
Formation & geological history
Formed by high-temperature and high-pressure metamorphic processes acting on pre-existing igneous or sedimentary rocks, typically during regional mountain-building events (orogenies) over millions of years.
Uses & applications
Used primarily in construction, as crushed stone for road bases, building facades, landscaping, and sometimes as dimension stone countertops.
Geological facts
Some of the oldest rocks on Earth, such as the Acasta Gneiss in Canada, are over 4 billion years old and provide crucial clues about the early history of the Earth's crust.
Field identification & locations
Easily identifiable in the field by its characteristic zebra-like alternating bands of light-colored quartz/feldspar and dark-colored micas/amphiboles. Commonly found in ancient continental shields and mountain cores.
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