metamorphic
Gneiss
Gneiss
Hardness of 6-7 on the Mohs scale, characterized by distinct alternating light and dark bands (gneissic banding), vitreous to dull luster, granular to foliated 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 bands (gneissic banding), vitreous to dull luster, granular to foliated structure, specific gravity around 2.6-2.9.
Formation & geological history
Formed by high-temperature and high-pressure metamorphic processes acting on pre-existing igneous or sedimentary rocks (such as granite or schist) deep within the Earth's crust, typically during continental collisions.
Uses & applications
Used primarily as dimension stone in construction, building facades, paving, and occasionally as decorative crushed stone for landscaping.
Geological facts
Gneiss contains some of the oldest known rocks on Earth, with certain formations dating back over 4 billion years, such as the Acasta Gneiss in Canada.
Field identification & locations
Easily identified in the field by its striking banded or striped appearance, distinguishing it from unbanded granites. Found worldwide in ancient cratons and shield areas.
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