metamorphic
Gneiss
Gneiss
Hardness of 6-7 on the Mohs scale, characterized by distinctive alternating light and dark mineral bands (gneissic banding), vitreous to dull luster, granular to foliated crystal structure, specific gravity of 2.6-2.9.
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Physical properties
Hardness of 6-7 on the Mohs scale, characterized by distinctive alternating light and dark mineral bands (gneissic banding), vitreous to dull luster, granular to foliated crystal structure, specific gravity of 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 shale) deep within the Earth's crust, typically during continental collisions.
Uses & applications
Used primarily as crushed stone for construction, road base, building facades, and dimension stone for landscaping.
Geological facts
Gneiss contains some of the oldest rocks found on Earth, with certain formations dating back over 4 billion years.
Field identification & locations
Identified by its bold alternating light and dark bands of minerals like quartz, feldspar, biotite, and hornblende. Commonly found in ancient continental shields.
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