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Igneous rock: Trachite
The crust is the outermost solid layer of the earth. It consists of igneous rock like basalt, metamorphic rock and sedimentary rock. Beneath the crust lies the mantle. The uppermost layer of the crust are the continents and the ocean floor. The crust is the upper part of the lithosphere.
The boundary between the crust and mantle is placed at the Mohorovi?i? discontinuity. This boundary can only be defined by seismological research and is presumably caused by differences in the materials the rock is composed of. The crust has a lower density that the mantle.
There are two types of crust, continental crust and oceanic crust. Beneath the oceans lies oceanic crust which is relatively thin, up to 10 kilometres thick. Oceanic crust consists of basalt, diorite and gabbro with a layer of deep-sea sediments on top.
Continental crust has a lower density than oceanic crust and consists of igneous rock, metamorphic rock and many types of sediments. The continental crust is 35-40 kilometres thick, but at mountain ranges this could be up to 80 kilometres.
The crust 'floats' on the earth's mantle, which is composed of plastic flowing rock. Plate tectonics means that plates float on the mantle. Because oceanic crust has a lower density it will move under continental crust when plates collide. This is called subduction.
A schematic representation of the inside of the Earth. 1 Continental crust, 2 Oceanic crust, 3 and 4 Earth's mantle 5 Outer core (liquid), 6 Inner core (solid), A Mohorovi?i? discontinuity, B Gutenberg discontinuity, C Lehmann discontinuity. Creative Commons License.
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