Partition of Mg and Fe2+ in coexisting pyroxenes

A general theory for the partition of elements between coexisting, multicomponent phases is outlined and applied to data for Ca-rich pyroxene (Cap) — Ca-poor pyroxene (Op) assemblages from the Skaergaard and Bushveld intrusions and from charnockites. The intercrystalline partition of Mg and Fe²⁺ are studied separately rather than through the exchange reaction, MgSiO ₃ ^Cap +FeSiO ₃ ^Op FeSiO ₃ ^Cap +MgSiO ₃ ^Op .The separate distributions for x_MgSiO3> and x_FeSiO3> are quite distinct and demonstrate directly that solutions of both Mg and Fe²⁺ in the two pyroxenes are nonideal.