The crystal structure of Ca[Zn8(SO4)2(OH)12Cl2](H2O)9, a new phase from slag dumps at Val Varenna, Italy
Burns, Peter C.; Roberts, Andrew C.; Nikischer, Anthony J.
European Journal of Mineralogy Volume 10 Number 5 (1998), p. 923 - 930
published: Oct 5, 1998
manuscript accepted: Mar 27, 1998
manuscript received: Sep 15, 1997
ArtNo. ESP147051005007, Price: 29.00 €
Abstract The new phase Ca[Zn8(SO4)2(OH)12Cl2](H2O)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) Å, V= 4142.7(9) A3, space group R3̄c, 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| ≥ 4σF] reflections collected using graphite-monochromated MoKα X-radiation and a CCD area detector. The structure contains two unique Zn positions; one is octahedrally coordinated by five OH- groups and one O2- anion, and the other is tetrahedrally coordinated by three OH- groups and one Cl- anion. The ZnlΦ6 (Φ: unspecified ligand) octahedra share edges to form brucite-type sheets with one-seventh of the octahedral sites vacant. The Zn2Φ4 tetrahedra are attached to the sheet of octahedra above and below the vacant site by sharing three anions with the ZnlΦ6 octahedra. The single unique S position is tetrahedrally coordinated by four O2- 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 H2O 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 CaΦ9 polyhedron. The structure is closely related to that of gordaite, NaZn4(SO4)(OH)6 • 6H2O