Metal Abundance and Availability

The average composition of the Earth s crust is essentially the composition of igneous rocks, since metamorphic and sedimentary rocks constitute a relatively insignificant portion of the total crustal mass. Eight elements - O, Si, Al, Fe, Ca, Na, K, and Mg - make up nearly 99% of the total elemental mass the remaining elements are differentiated throughout the crust according to their particular 

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With regard to geochemical cycling (as well as for economic considerations), it is important to distinguish between the abundance of an element and its availability. The availability of an element is related not only to its relative abundance on Earth but also the stability of minerals in which it is a major constituent. Thus, a number of elements (e.g. copper, mercury, tin, and arsenic) that are scarce in terms of their average crustal abundance are easily isolated due to their ability to form mineral deposits. The most unavailable elements are those that form no major minerals of their own. Many of the rarer elements are available for economic use only to the extent that they are obtained as byproducts of the extraction of more abundant elements. Tellurium, for example, is produced during the electrolytic refining of copper. 

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