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gneiss

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Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under pressures ranging from 2 to 15 kbar, sometimes even more, and temperatures over 300 °C (572 °F). Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage.

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Gneiss is a common metamorphic rock created when existing igneous or sedimentary rocks are subjected to extreme heat and pressure deep underground. It's recognizable by its distinctive banded appearance, with alternating stripes of darker and lighter colors, and forms under conditions involving pressures of 2 to 15 kilobars or more and temperatures exceeding 300°C.

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Key facts

Rock.name: Gneiss
Rock.type: Metamorphic
Rock.image: Gneiss.jpg
Rock.caption: Sample of gneiss exhibiting "gneissic banding"

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Image: Gneiss.jpg

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Commons category: Gneiss

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Article

15 sections

Contents

Description
Gneissic banding
Augen gneiss
Migmatite
Occurrences
Granite-greenstone belts
Gneiss domes
Examples
Etymology
Uses
See also
References
Citations
Further reading
External links

Gneiss ( ) is a common and widely distributed type of metamorphic rock. It is formed by high-temperature and high-pressure metamorphic processes acting on formations composed of igneous or sedimentary rocks. This rock is formed under pressures ranging from 2 to 15 kbar, sometimes even more, and temperatures over 300 °C (572 °F). Gneiss nearly always shows a banded texture characterized by alternating darker and lighter colored bands and without a distinct cleavage.

Gneisses are common in the ancient crust of continental shields. Some of the oldest rocks on Earth are gneisses, such as the Acasta Gneiss.

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Categories

Gneiss Industrial minerals Metamorphic rocks