metamorphic
Banded Gneiss
Gneiss
Hardness of 6-7 on the Mohs scale, characterized by distinct alternating light and dark bands (gneissic banding) composed of quartz, feldspar, and dark minerals like biotite or hornblende. Luster ranges from dull to vitreous.
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Physical properties
Hardness of 6-7 on the Mohs scale, characterized by distinct alternating light and dark bands (gneissic banding) composed of quartz, feldspar, and dark minerals like biotite or hornblende. Luster ranges from dull to vitreous.
Formation & geological history
Formed by high-temperature and high-pressure regional metamorphic processes altering pre-existing rocks such as granite or sedimentary rocks deep within the Earth's crust.
Uses & applications
Used primarily in the construction industry as crushed stone for roadbeds, building foundations, and sometimes as decorative dimension stone.
Geological facts
Gneiss includes some of the oldest rocks found on Earth, with certain formations dating back over 4 billion years.
Field identification & locations
Identified by its striking compositional banding and interlocking crystalline texture. Commonly found in ancient shield areas of continents.
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