Structure of the Earth discontinuity (a second order discontinuity). The uppermost mantle together with the crust constitutes the lithosphere. The crust-mantle boundary occurs as two physically different events. First, there is a discontinuity in the seismic velocity, which is most commonly known as the Mohorovičić discontinuity or Moho. The cause of the Moho is thought to be a change in rock composition from rocks containing plagioclase feldspar (above) to rocks that contain no feldspars (below). Second, in oceanic crust, there is a chemical discontinuity between ultramafic cumulates and tectonized harzburgites, which has been observed from deep parts of the oceanic crust that have been
Primary minerals in the acidic igneous rocks and a second group of accessory minerals which were formed by deposition from the residual mother liquors. Modern soil science offers the following definition: "Primary Minerals: The thickness of the earth's crust varies from 10 km under the ocean to 30 km under the continents. Of the 88 naturally occurring elements on earth, only 8 make [up] most of the crust. The earth's crust and soils are dominated by the silicic acid in combination with Na, Al, K, Ca, Fe and O ions. ...Those elements are components of primary minerals, whereas primary minerals are components