The crystal structure of kukisvumite, Na6ZnTi4(Si2O6)4O4·4H2O

The crystal structure of kukisvumite, a rare mineral from Kola peninsula, Russia, has been refined in the Pccn space group with X-ray single-crystal data to R = 0.055. Kukisvumite, ideally Na6ZnTi4(Si2O6)4O4·4 H2O, has a = 29.029(4) Å, b = 8.595(1) Å, c = 5.209(1) Å, and Z = 2. Its crystal structure is closely related to that of lintisite; the latter mineral is obtained from kukisvumite through the substitution Zn2+ + vacancy = 2 Li+. In the Pccn space group an average structural model is realized, resulting in columns of half-occupied [ZnO4] tetrahedra and in zig-zag chains of half-occupied Na-centered octahedra. The actual structure of kukisvumite would imply a concerted ordering of zinc and sodium in neighbour cells. The polysomatic relationships of kukisvumite with the minerals of the lintisite family are shortly outlined