The crystal structure of Ca[Zn (sub 8) (SO (sub 4) ) (sub 2) (OH) (sub 12) Cl (sub 2) ](H (sub 2) O) (sub 19) , a new phase from slag dumps at Val Varenna, Italy

The new phase Ca[Zn (sub 8) (SO (sub 4) ) (sub 2) (OH) (sub 12) Cl (sub 2) ](H (sub 2) O) (sub 9) has been discovered on a specimen from slag dumps at Val Varenna, Italy. The crystal structure, rhombohedral, a = 8.3797(4), c = 68.123(5) A, V= 4142.7(9) A (super 3) , space group R3c, Z = 6, has been determined and refined to an agreement index (R) of 4.9% and a goodness-of-fit (S) of 1.11 for 713 unique observed [1F > or = 4sigma (sub F) ] reflections collected using graphite-monochromated MoKalpha X-radiation and a CCD area detector. The structure contains two unique Zn positions; one is octahedrally coordinated by five OH (super -) groups and one O (super 2-) anion, and the other is tetrahedrally coordinated by three OH (super -) groups and one Cl (super -) anion. The ZnlPhi (sub 6) (Phi : unspecified ligand) octahedra share edges to form brucite-type sheets with one-seventh of the octahedral sites vacant. The Zn2Phi (sub 4) tetrahedra are attached to the sheet of octahedra above and below the vacant site by sharing three anions with the ZnlPhi (sub 6) octahedra. The single unique S position is tetrahedrally coordinated by four O (super 2-) anions, and is linked to the tetrahedral-octahedral sheet by a single shared ligand. The structure contains one unique Ca position that is coordinated by nine H (sub 2) O groups; it is located in an interlayer position. A network of H bonds provide additional connectivity within the tetrahedral-octahedral sheet, as well as the only linkages between the tetrahedral-octahedral sheets and the interlayer CaPhi (sub 9) polyhedron. The structure is closely related to that of gordaite, NaZn (sub 4) (SO (sub 4) )(OH) (sub 6) . 6H (sub 2) O.