Where is gneiss formed

A sample from Karelia, Russia. This specimen has a composition of an ordinary granite: pink K-feldspar, gray quartz, and black biotite.

Width of sample 11 cm. It was originally a mining term, meaning a country rock in the Ore Mountains Erzgebirge which contained metalliferous veins.

The term gneist was first recorded in print by Agricola Georg Bauer in his famous posthumously published book De Re Metallica which remained the most important mineralogy and mining textbook for the next two centuries. The book was published in 1. Most of the mineral grains of gneissose rocks are visible to the naked eye.

Banding in this rock is a result of mineral segregation into separate, typically light- and dark-colored layers. Light-colored layer is usually composed of feldspars and quartz.

Most important dark minerals are hornblende and biotite. Individual bands are usually mm in thickness. Layers larger than that imply that partial melting or the introduction of new material have probably taken place. Such rocks are called migmatites. It is often difficult to distinguish it from migmatite because there is a gradational transition from one to another. It is not well understood how the segregation takes place, but it must be the result of extreme pressure and shear stress deep in the crust.

The protolith of gneiss may be an igneous rock , in this case it is called an orthogneiss. Department of Earth, Atmospheric, and Planetary Sciences. Part of the EASP Geology Walk Gneiss is a metamorphic rock formed by changing schist, granite, or volcanic rocks through intense heat and pressure.

Point to an item below for more help. Other specimens - Click the thumbnails to enlarge. Introduction Features Igneous rocks Sedimentary rocks Metamorphic rocks. For further information, take a look at our frequently asked questions which may give you the support you need. Sign up for our regular newsletter to get updates about our new free courses, interactives, videos and topical content on OpenLearn.

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