The crystal structure of metavoltine from Sierra Gorda, Chile, has been solved from photographic X-ray data by the heavy atom method. The space group used wasP3 witha=9.575(5) andc=18.17(1)A; cell content: K2Na6 (Fe2+, Cu, Zn)Fe 6 3+ (SO4)12O2·18H2O. From the relatively small number and the somewhat poor quality of the X-ray data, the least squares refinement did not give very satisfactory results-especially so for the light atoms. Therefore, steric considerations and information from the Fourier maps were also used when choosing the final atomic coordinates. The salient features of the structure are clusters of Fe 3 3+ O(H2O)3(SO4)6 with Fe3+ in octahedral coordination, and Fe2+(H2O)6 octahedra. The Na+ ions show octahedral coordination, the K+ ions irregular nine coordination.