Physical mixtures and coprecipitates of magnesium and divalent iron oxalates having molar ratios of 1:1, 1:2 and 1:4 were prepared Comparisons were made between the thermal decomposition of the physically mixed oxalate and the coprecipitated oxalate having the same composition. Samples were studied by thermogravimetry (TG), thermomagnetometry (TM), differential thermal analysis (DTA), mass spectroscopic evolved gas analysis (EGA), and powder X-ray diffraction from 25 to 1400 degrees C in both oxidizing and inert atmospheres. Coprecipitates were expected to be solid solutions, showing only single weight losses for the dehydration and decomposition steps. This is true for the coprecipitates having more iron present than magnesium. In contrast, the physical mixtures were expected to behave as separate materials, showing two separate weight losses for dehydration and decomposition. This held true except for the dehydration step, which takes place as one weight loss. TM and X-ray diffraction results indicate the coprecipitate forms magnesium ferrite (MgFe2O4) more readily than the equivalent physically mixed material. An oxidizing atmosphere was necessary to facilitate the production of magnesium ferrite.