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APES Minerals and the Environment

Terms in this set (59)

Basically because each element is chemically unique, and therefore behaves differently to other elements in given conditions.
Take for example crystallization from a magma. As the magma cools, certain elements are able to form stable crystalline structures (minerals). Different minerals can start to crystallize at different temperatures, and different minerals have completely different chemistries. So, for example, pyroxene (which crystallizes early) can crystallize out lots of aluminium, whereas quartz (which forms late) mostly only crystallizes out silica. This gets even more complicated when you realize some elements can substitute for others in crystal structures, so for example Europium can be preferentially substituted into plagiclase feldspar in place of Calcium.
This kind of chemical differentiation is very common, and there's lots of different processes in which it is important. But there's other differentiation processes too. For example, simple density sorting can be really important. The reason we find large concentrations of gold in many places is because gold-rich rocks have been eroded by rivers, and the gold grains have been deposited by those rivers simply due to density contrast. That leads to a secondary 'placer' deposit of gold which is far more enriched than the rocks from which the gold originally came.
The processes which form oceanic crust are different to those which form continental crust, so again the mineral assemblages (and therefore elemental distributions) of the two systems are very different.