The crystal structure of kukisvumite, Na6ZnTi4(Si2O6)(4)O-4 center dot 4 H2O

The crystal structure of kukisvumite, a rare mineral from Kola peninsula, R ussia, has been refined in the Peen space group with X-ray single-crystal d ata to R = 0.055. Kukisvumite, ideally Na6ZnTi4(Si2O6)(4)O-4 . 4H(2)O. has a = 29.029(4) Angstrom, b = 8.595(1) Angstrom, c = 5.209(1) Angstrom, and Z = 2. Its crystal structure is closely related to that of lintisite; the la tter mineral is obtained from kukisvumite through the substitution Zn2+ + s quare = 2 Li+ In the Peen space group an average structural model is realiz ed, resulting: in columns of half-occupied [ZnO4] tetrahedra and in zig-zag chains of half-occupied Na-centered octahedra. The actual structure of kuk isvumite would imply a concerted ordering of zinc and sodium in neighbour c ells. The polysomatic relationships of kukisvumite with the minerals of the lintisite family are shortly outlined.