The geochemical classification of the elements, also called the Goldschmidt classification because it is the result of work undertaken in the 1920s by the chemist Victor Goldschmidt, provides an understanding of the origin of the various proportions of chemical elements in the Earth's minerals and rocks, and more generally in the rocks of planets and meteorites.
It comes from the analysis of the various mineralogical phases in the crystallisation of a magma. It has been found that elements have a tendency to collect together in the various phases.
The different classes of element
Goldschmidt introduced four classes of element:
- lithophiles, which have a dominant affinity for oxygen and consequently occur with aluminates and silicates;
- chalcophiles, which have a dominant affinity for sulphur (literally: "having an affinity for copper" due to an error by Victor Goldschmidt on originally giving the name which he thought meant "having an affinity for sulphur") ;
- siderophiles, which have a dominant affinity for iron. This explains why metals such as gold and platinum are rare in the Earth's crust, having migrated with iron during the formation of the Earth's core;
- atmophiles, which have a dominant affinity for fluid phases. Thus hydrogen is an atmophile because it occurs on Earth essentially in sea water. The same is true for nitrogen and the inert gases.
The geochemist Victor Moritz Goldschmidt. © The Geological Society of London