metamorphic
Gneiss
Gneiss
Hardness of 6-7 on the Mohs scale, characterized by distinct alternating light and dark compositional bands (gneissic banding) with a granular and foliated structure.
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Physical properties
Hardness of 6-7 on the Mohs scale, characterized by distinct alternating light and dark compositional bands (gneissic banding) with a granular and foliated structure.
Formation & geological history
Formed by high-temperature and high-pressure metamorphic processes acting on pre-existing igneous rocks (like granite) or sedimentary rocks (like shale) deep within the Earth's crust.
Uses & applications
Commonly used in construction, as crushed stone for roadbeds, building facades, and dimension stone.
Geological facts
Gneiss contains some of the oldest rocks found on Earth, with certain formations dating back over 4 billion years.
Field identification & locations
Easily identified by its characteristic zebra-like banding of light-colored minerals (quartz and feldspar) and dark-colored minerals (biotite and hornblende). Found worldwide in ancient shield areas.
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