Summary: The maghemitization process, by which magnetic minerals with spinel structure become progressively oxidized but remain single phase spinels, seems to be an important feature of submarine weathering. Whether the process takes place by the minerals acquiring oxygen from the sea-water or by the sea-water leaching out iron, the controlling process is the diffusion of Fe²⁺ in the spinel structure. Magnetic studies have suggested that during maghemitization the availability for oxidation of Fe²⁺ in the tetrahedral (A) sites of the spinel structure is much less than that in octahedral (B) sites. In this study the Fe²⁺-containing spinels FeAl₂O₄, FeCr₂O₄, FeGa₂O₄, and Fe₂GeO₄, in which Fe²⁺ is predominantly in either A or B sites were prepared, and the diffusion of Fe²⁺ was studied by (1) interdiffusion experiments with the Mg²⁺ counterparts and (2) oxidation experiments in air. Fe₂GeO₄ (Fe²⁺ in B sites) was found to be associated with a higher interdiffusion coefficient and lower activation energy than FeAl₂O₄ (75% Fe²⁺ in A sites). Oxidation/diffusion activation energies of 0.27 and 0.71 eV were assigned to Fe²⁺ in B and A sites respectively. The experiments thus provide support for the maghemitization model in which Fe²⁺ in B sites is preferentially oxidized.