TY - JOUR

T1 - Comparative crystal-structure study of Ag-free lilliantite and galenobismutite from vulcano, Aeolian Islands, Italy

AU - Pinto, Daniela

AU - Balic Zunic, Tonci

AU - Garavelli, Anna

AU - Makovicky, Emil

AU - Vurro, Filippo

PY - 2006

Y1 - 2006

N2 - The crystal structures of natural Ag-free lillianite of fumarolic origin from Vulcano, Aeolian Islands, Italy, Pb2.88Bi2.12(S5.67 Se0.33)S6.00, with a 13.567(1), b 20.655(2), c 4.1216(4) Å, V 1155.0(2) Å3, space group Bbmm, Z = 4, and galenobismutite also from Vulcano, Pb1.00Bi2.03(S3.87Se0.11)¿3.98, with a 11.815(2), b 14.593(2), c 4.0814(6) Å, V 703.7(2) Å3, space group Pnam, Z = 4, were refined from single-crystal X-ray data. The refi nements converge to R = 3.40% [for 745 refl ections with Fo > 4(Fo)], and R = 2.96% [for 607 reflections with Fo > 4(Fo)] for Ag-free lillianite and galenobismutite, respectively. In Ag-free lillianite, the trigonal prism M3 is occupied only by Pb, whereas both the octahedrally coordinated M1 and M2 sites are mixed (Pb,Bi) positions. The same octahedra incorporate both the surplus of Bi and vacancies () created by the substitution 3Pb2+ ¿ 2Bi3+ + , which allows for the observed deviations from the ideal composition, Pb3Bi2S6. Selenium is preferentially ordered at the six-fold and fi ve-fold coordinated anionic sites, whereas the four-fold coordinated site S3 remains free of Se. The known structural arrangement of galenobismutite was confi rmed in this work. The octahedrally coordinated M1gb site was found to be a ful  Bi position. Some evidence of Pb-Bi disorder has been observed at both the M2gb (Bi-dominated) and M3gb (Pb-dominated)positions. A heterogeneous distribution of Se in the anionic S sites was observed in galenobismutite. Atoms of Se are mainlyconcentrated at the site S1, and less so in the other anionic sites.

AB - The crystal structures of natural Ag-free lillianite of fumarolic origin from Vulcano, Aeolian Islands, Italy, Pb2.88Bi2.12(S5.67 Se0.33)S6.00, with a 13.567(1), b 20.655(2), c 4.1216(4) Å, V 1155.0(2) Å3, space group Bbmm, Z = 4, and galenobismutite also from Vulcano, Pb1.00Bi2.03(S3.87Se0.11)¿3.98, with a 11.815(2), b 14.593(2), c 4.0814(6) Å, V 703.7(2) Å3, space group Pnam, Z = 4, were refined from single-crystal X-ray data. The refi nements converge to R = 3.40% [for 745 refl ections with Fo > 4(Fo)], and R = 2.96% [for 607 reflections with Fo > 4(Fo)] for Ag-free lillianite and galenobismutite, respectively. In Ag-free lillianite, the trigonal prism M3 is occupied only by Pb, whereas both the octahedrally coordinated M1 and M2 sites are mixed (Pb,Bi) positions. The same octahedra incorporate both the surplus of Bi and vacancies () created by the substitution 3Pb2+ ¿ 2Bi3+ + , which allows for the observed deviations from the ideal composition, Pb3Bi2S6. Selenium is preferentially ordered at the six-fold and fi ve-fold coordinated anionic sites, whereas the four-fold coordinated site S3 remains free of Se. The known structural arrangement of galenobismutite was confi rmed in this work. The octahedrally coordinated M1gb site was found to be a ful  Bi position. Some evidence of Pb-Bi disorder has been observed at both the M2gb (Bi-dominated) and M3gb (Pb-dominated)positions. A heterogeneous distribution of Se in the anionic S sites was observed in galenobismutite. Atoms of Se are mainlyconcentrated at the site S1, and less so in the other anionic sites.

KW - Faculty of Science

KW - Italien

KW - vulkan

KW - krystal strukturer

KW - Ag-free lillianite

KW - Italy

KW - Vulcano

KW - fumaroles

KW - crystal structure

KW - galenobismutite

M3 - Journal article

VL - 44

SP - 159

EP - 175

JO - Canadian Mineralogist

JF - Canadian Mineralogist

SN - 0008-4476

ER -