The crystal structure of erdite, NaFeS2*2H2O

The crystal structure of the new mineral erdite, NaFeS2.2H2O, has been determined from 263 counter-measured intensity data. The mineral is monoclinic, space group A/c, with a : 10.693(l), D : 9.1l5(l), c : s.507(4)4, B : 92.t7(2), Z : 4, D (X-ray) :2.217 g/cm3. Because of the poor quality of the crystals, the reliability index after anisotropic refinement was not better than 0.170, but the structure is clearly defined. FeSo tetrahedra form chains along the c direction by sharing edges. Each Na atom is coordinated to one edge of an FeSo tetrahedron, and to four HrO molecules. The Fe-S bond length is 2.25(l)A. The (FeSr), chain is very regular and consistent with the dimensions of similar chains previously described in KFeSr, RbFeSr, CsFeSr, and TlFeSr.