Lecture 5
Nomenclature for Trace Element Classification
We have already grouped elements into two classes, major elements and trace
elements (Figure 1). In addition, there are many ways of classifying trace elements.
Examples are:
1) Siderophile elements: elements that concentrate in metallic iron such as Ni,
Co, Os, Ir
Chalcophile elements: elements that concentrate in sulfides, such as Se, As,
Zn, Cd
Lithophile clements: elements that concentrate in silicate phases, such as Rb,
Sr, Ba, Nb, Ta, Th, U, REE
Atmophile elements: naturally occurring gaseous elements such as N and rare
gases
These definitions are useful when considering formation of major earth
reservoirs, i.e., core, mantle, crust and atmosphere.
2) Compatible and Incompatible elements: In an equilibrium system composed
of minerals and coexisting silicate melt, compatible elements are
preferentially partitioned into the solid phases and incompatible elements are
preferentially partitioned into the melt. This terminology is commonly used in
the context of partial melting of mantle rocks to form basaltic magma. Upper
mantle rocks are rich in olivine and pyroxenes and the elements Sc, Cr, Co
and Ni are compatible (enriched) in these phases relative to a silicate melt.
However, a key aspect of this definition is to specify what mineral phases are
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