Summary: The recently described electrolysis of molten basalt (Oppenheim, 1968) gave indefinite results with regard to the behaviour of iron. Repeating the experiments in an inert atmosphere has shown that ferric iron moves towards the anode, and ferrous iron to the cathode. All metallic ions of valency three and more are now seen to be concentrated towards the anode, with relative enrichments in decreasing order: Fe³⁺, P, Ti, Si, and Al; and oxygen gas is released at the anode. Metals of valency one and two are concentrated towards the cathode with relative enrichments in decreasing order: Na, Fe²⁺, K, Ca, Mn, and Mg.

The series expected to be differentiated within a magma consequent upon its electrolysis is redefined. The absence of natural analogues suggests either the non-operation of suitable electric currents within magmas, or the destruction of their effects by convection, fractional crystallization, or both. An electrolytic process is feasible at the mantle-core boundary, leading mainly to deposition of iron on the core and release of oxygen upwards.