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 of parent rocks. There are almost 3000 known minerals, but only 20 are common and just 10 minerals make up 90 % of the earth's crust. Primary minerals are defined as minerals found in soil but not formed in soil. This definition is different from that of secondary minerals, which are defined as minerals formed in soils." This is further defined by Dr. Broome of North Carolina State: Two types of minerals are found in natural systems: primary and secondary. Primary rocks are the source of primary minerals and primary water. Primary minerals A primary mineral is any mineral formed