A material suitable for use as the active anode surface in the electrolytic reduction of alumina to aluminium metal defined by the formula: A.sub.1+xB.sub.1+.delta.C.sub.dO.sub.4 where A is a divalent cation or a mixture of cations with a relative preference for octahedral coordination, B is a trivalent cation or mixture of cations with a relative preference for tetrahedral coordination, C is a trivalent cations with a relative preference for octahedral coordination or a four-valent cation with a relative preference for octahedral coordination, O is the element oxygen: When C is trivalent x=0, 0.8