Gneiss facts for kids
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Gneiss is a type of metamorphic rock. The minerals in gneiss may come from rocks which were originally either igneous or sedimentary. They were heated and squeezed, and the minerals recrystallized.
Orthogneiss is gneiss got from igneous rock (such as granite). Paragneiss is gneiss got from sedimentary rock (such as sandstone).
In gneisses, minerals tend to be foliated: layered and segregated into bands. Thus there are seams of quartz and of mica in a mica schist, very thin, but consisting essentially of one mineral.
Lewisian gneiss
The Lewisian complex or Lewisian Gneiss is a suite of Precambrian metamorphic rocks that outcrop in the northwestern part of Scotland, forming part of the Hebridean Terrane. These rocks are of Archaean and Palaeoproterozoic age, ranging from 3.0–1.7 Ga.
Images for kids
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Orthogneiss from the Czech Republic
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Pure shear deformation of rock producing gneissic banding. The undeformed rock is shown at upper left, and the result of pure shear deformation at upper right. At lower left is the stretching component of the deformation, which compresses the rock in one direction and stretches it in the other, as shown by the arrows. The rock is simultaneously rotated to produce the final configuration, repeated at lower right.
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Dark dikes (now foliated amphibolites) cutting light grey Lewisian gneiss of the Scourie complex, both deformed and cut by later (unfoliated) pink granite dikes
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Contact between a dark-colored diabase dike (about 1100 million years old) and light-colored migmatitic paragneiss in the Kosterhavet National Park in the Koster Islands off the western coast of Sweden.
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Sample of Sete Voltas gneiss from Bahia in Brazil, the oldest rock outcropping in the crust of South America, c. 3.4 billion years old (Archean)
See also
In Spanish: Gneis para niños
