The crystal structure of nikischerite, Na Fe2+6 Al3 (SO4)2 (OH)18 (H2O)12, a mineral of the shigaite group

The crystal structure of nikischerite, Na Fe62+Al3 (SO4)(2) (OH)(18) (H2O)(12), rhombohedral, a 9.347(1), c 33.000(7) Angstrom, V 2497(3) Angstrom(3), Z = 3, R (3) over bar, has been refined to an R index of 6.4% using 444 observed reflections measured with MoKalpha X-radiation. The structure of nikischerite consists of planar [AlFe2+(OH)(6)] sheets of octahedra that are intercalated with (Na{H2O}(6)) octahedra, (SO4) tetrahedra and (H2O) groups, all units being linked by hydrogen bonds. Nikischerite is isostructural with shigaite, Na Mn-6(2+) Al-3(SO4)(2)(OH)(18)(H2O)(12), and motukoreaite, ideally Na Mg-6 Al-3 (SO4)(2) (OH)(18) (H2O)(12).