The defect structure of the synthetic anhydrous hausmanite (\mathrm{Mn}{3} \mathrm{O}{4}) has been investigated by (\mathrm{X})-ray powder diffraction and chemical analysis. The integrated intensity ratios of X-ray reflections, the unitcell constant values, and the (\mathrm{Mn}^{3+}) content in samples evidence the nonstoichiometry of hausmanite. The degree of oxidation of manganese, (\mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}), varied in the ranges of 2.05 to 3.04. The main type of defects is the cation vacancies, the anionic sublattice remains virtually unaffected. The distribution of (\mathrm{Mn}^{3+}) ions and of cation vacancies over the positions of both spinel cationic sublattices depends on the oxidation degree of manganese. For (\mathrm{Mn}^{3+} / \mathrm{Mn}^{2+} \leq 2.4) the vacancies are created merely on the tetrahedral sites and for (\mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}>2.4) the excess of vacancies is distributed at random over the tetrabedral and octahedral sites according to the formula (\mathrm{Mn}{38-3 x}^{2+} \mathrm{Mn}{2 x}^{3+} \square_{x}\left[\mathrm{Mn}{16}^{3+}\right] \mathrm{O}{32}) for (x \leq 1 / 3) and (\mathrm{Mn}{(8-3 x)}^{2+} \mathrm{Mn}{(5 x / 2-1 / 6)}^{3+} \square_{(x / 2+1 / 6)}\left[\mathrm{Mn}{(99 / 6-\mathrm{x} / 2)}^{3+} \square(x / 2-1 / 6)\right] \mathrm{O}{32}) for (x>1 / 3). The lattice constants vary in the ranges (a=0.8148-0.8150 \mathrm{~nm}) and (c=0.9466-0.9464 \mathrm{~nm}) for (\mathrm{Mn}^{3+} / \mathrm{Mn}^{2+}) varying from 2.05 to 3.04. 1993 Academic Press, Inc.