Hydrothermal experiments on the join Fe3O4–Fe2TiO4 are consistent with—but do not conclusively prove—the existence of a miscibihty gap having a consolute temperature of 565±15°C and composition near Mt55Usp45 for the pure magnetite–ulvöspinel join. These results appear to conflict with the conclusion of Price (preceding paper) that the consolute point for natural magnetite–ulvöspinel intergrowths lies at or below 490°C. The experiments can be reconciled if (a) the presence of several percent MgO in the natural specimens depresses the consolute point, or (b) the experiments reported here failed to attain equilibrium—a real possibility since they have not been strictly reversed.

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