Ce(IV)-Ce(III) and Fe(III)-Fe(II) redox equilibria in Ca-Mg-Al -silicate melts have been individually measured with respect to the base composition, melt temperature, imposed oxygen fugacity, and multivalent elemental concentration. The mutual interaction of these two redox couples has been studied in analogous glasses which simultaneously contained iron and cerium. Analysis of Fe(III) concentrations in iron-cerium glasses by electron paramagnetic resonance and optical adsorption spectroscopy indicate that Ce(IV) is stoichiometrically reduced by Fe(II) in the melt to produce Fe(III) and Ce(III) and that Ce(III)-O-Fe(III) complexes are formed int he melt. Consequently, it is concluded that cerium exists only as Ce(III) in basaltic magmas; cerium anomalies cannot be ascribed to the stabilisation of Ce(IV) in magmas.
