National Bureau of Standards

A series of compositions in the system Fe3O4-Mn3O4 was prepared and examined at high temperatures by X-ray diffraction methods. Although Fe3O4 and Mn3O4 form a con-tinuous series of substitutional solid solutions stable at room temperatures, those composi-tions containing less than 60 percent of Mn3O4 are cubic, of the spinel type, and the rest are tetragonal. Those compositions that are tegragonal at room temperature pass through a two-phase region when heated and acquire the cubic spinel-type structure at high tempera-tures. The temperature range of the two-phase (exsehlfion) region varies with composition. The relation to this system of the minerals vredenburgite and hausmannite is discussed. I