Abstract
The diadochic substitution of elements in the structure of silicate minerals is primarily controlled by the potential energies arising from the linkage of vicarious cations with an oxygen anion. A quantity, the index of diadochy, is proposed as a measure for the contribution of a cation to the potential energy, and is calculated for a number of elements of geological significance. The indices of diadochy of the elements harmonize generally with the natural geochemical behavior of the elements. Furthermore, possible effects of controlling factors other than the index of diadochy on the substitution are considered.
