The crystal structure of 7H:12Q cannizzarite from Vulcano, Italy.

TY - JOUR

T1 - The crystal structure of 7H:12Q cannizzarite from Vulcano, Italy.

AU - Topa, D.

AU - Makovicky, Emil

AU - Dittrich, H.

PY - 2010/6

Y1 - 2010/6

N2 - The crystal structure of cannizzarite, ideally Pb48Bi 56(S124Se8)132 a fumarole sublimate from the La Fossa crater, on the island of Vulcano, Italy, with a nominal composition Pb47.9 Bi55.8(S121.8Se 10.5)σ132.2 and unit-cell parameters a 38.86(3), b 4.090(3), c 39.83(3) Ȧ, β 102.30(3)°, Z= 1, has been solved and refined in space group P21/m from X-ray single-crystal diffraction data, to an R1 of 10.7% on the basis of 3612 unique reflections with [F0 > 4σ(F0)]; the data were collected on a Bruker P3 diffractometer with a CCD detector and MoKα radiation.The cannizzarite crystal studied has 104 cations and 132 anions in a unit cell. Refinement shows that about eight anions per cell contents are selenium, the bulk being sulfur. The crystal structure is composed of pseudotetragonal layers (Q layers), two cation-anion planes thick, of the (100)pbs type that alternate with double-octahedron pseudohexagonal layers (H layers) of the (111)pbs type. Both types of layer contain Pband Bi; their distribution was studied by means of bond-valence calculations, polyhedron characteristics and bond-length ratios of the opposing Me-anion bonds. The unit-cell contents are Me48X48 for the Q layers, and Me56X84 for the H layers. Selenium was found only in H layers. The structure determined represents the shorter of the two modules, Pb12Bi14S33 and Pb17Bi 20S47, found in the structure of synthetic cannizzarite proposed earlier, and proves their independent existence.

AB - The crystal structure of cannizzarite, ideally Pb48Bi 56(S124Se8)132 a fumarole sublimate from the La Fossa crater, on the island of Vulcano, Italy, with a nominal composition Pb47.9 Bi55.8(S121.8Se 10.5)σ132.2 and unit-cell parameters a 38.86(3), b 4.090(3), c 39.83(3) Ȧ, β 102.30(3)°, Z= 1, has been solved and refined in space group P21/m from X-ray single-crystal diffraction data, to an R1 of 10.7% on the basis of 3612 unique reflections with [F0 > 4σ(F0)]; the data were collected on a Bruker P3 diffractometer with a CCD detector and MoKα radiation.The cannizzarite crystal studied has 104 cations and 132 anions in a unit cell. Refinement shows that about eight anions per cell contents are selenium, the bulk being sulfur. The crystal structure is composed of pseudotetragonal layers (Q layers), two cation-anion planes thick, of the (100)pbs type that alternate with double-octahedron pseudohexagonal layers (H layers) of the (111)pbs type. Both types of layer contain Pband Bi; their distribution was studied by means of bond-valence calculations, polyhedron characteristics and bond-length ratios of the opposing Me-anion bonds. The unit-cell contents are Me48X48 for the Q layers, and Me56X84 for the H layers. Selenium was found only in H layers. The structure determined represents the shorter of the two modules, Pb12Bi14S33 and Pb17Bi 20S47, found in the structure of synthetic cannizzarite proposed earlier, and proves their independent existence.

M3 - Journal article

SN - 0008-4476

VL - 48

SP - 483

EP - 495

JO - Canadian Mineralogist

JF - Canadian Mineralogist

IS - 3

ER -