Trace element groupings in the periodic table

Trace elements are often studied in groups, and deviations om group behaviour or systematic cj ges in behaviour within the group are used as an indicator of petrological professes. The assodation of like trace elements also helps to sunplify what can otherwise be a very unwieldy data-set Trace elements are normally classified either on the basis of their position in the periodic table or according to their behaviour in magmatic systems. 

The periodic table of the elements, showing three main groups of trace elements, which are often treated together in geochemistry because of their relative positions in the table. These are the elements of the first transition series, the platinum group elements and the rare earth elements. The elements which are shaded are also Important trace elements in geochemistry. 

The elements in each of these respective groups have similar chemicai propernes and for this reason are expected to show similar geochemic behaviour. This is not always the case, however, because geological processes can take advantage of subtle chemical differences and fractionate elements of a group one from the other. Thus one of the tasks of trace element geochemistry is to discover which geological processes may have this effect and to quantify the extent of a particular process. 

Trace element When the Earth s mantle is melted, trace elements display a preference either for behaviour in the melt phase or the solid (mineral) phase. Trace elements whose preference is the magmatic sterns mineral phase are described as compatible, whereas elements whose preference is the melt are described as incompatible — i.e. they are incompatible in the mineral structure and will leave at the first available opportunity. Incompatible elements have also been called hygromagmatophile, a term first introduced by Treuil and Varet(1973). 

In detail there are degrees of compatibilty and incompatibility and trace elements win vary in their behaviour in melts of a different composition. For example, P is incompatible in a mantle mineralogy and during partial melting will be quickly concentrated in the melt. In granites, however, even though P is present as a trace element, it is compatible because it is accommodated in the structure of the minor phase apatite. 

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