COMPARATIVE CRYSTAL-STRUCTURE STUDY OF Ag-FREE LILLIANITE AND GALENOBISMUTITE FROM VULCANO, AEOLIAN ISLANDS, ITALY

Pinto, Daniela; Balić-Žunić, Tonči; Garavelli, Anna; Makovicky, Emil; Vurro, Filippo

doi:10.2113/gscanmin.44.1.159

Cited by 31 publications

(33 citation statements)

References 26 publications

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“…However, the calculation of the valence sum for such a Pb site gave only a slight improvement over the site on the symmetry plane (1.82 instead of 1.79), which shows that the coordination change is not very significant. The above evidence suggests, as already observed in the structure of lillianite (Pinto et al 2006a) that the large anisotropy of the displacement parameters can be caused by a dynamic disorder of the Me1 atom over the two close sites out of the symmetry plane, or be a consequence of large movements inside a large coordination polyhedron.…”

Section: Experimental Methodssupporting

confidence: 74%

Structure refinement of Ag-free heyrovskyite from Vulcano (Aeolian Islands, Italy)

Pinto

Balić-Žunić

Garavelli

et al. 2011

American Mineralogist

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The first single-crystal structure refinement of Ag-and Cu-free heyrovskýite was performed in this study. Crystals investigated were sampled from the high-temperature fumaroles of La Fossa crater of Vulcano, Aeolian Islands, Italy. Electron microprobe analyses gave the average chemical formula (Pb 5.86 Cd 0.03 ) Σ5.89 Bi 2.04 (S 8.52 Se 0.53 Cl 0.03 ) Σ9.08 , which is very close to the ideal composition of heyrovskýite, Pb 6 Bi 2 S 9 . Lattice parameters are a = 13.7498(4), b = 31.5053(8), c = 4.1475(1) Å, V = 1796.7(1) Å 3 , space group Bbmm. The structure refinement converges to R = 4.17% for 1312 reflections with F o > 4σ(F o ).In Ag-free heyrovskýite from Vulcano, as well as in the synthetic Pb 6 Bi 2 S 9 , the trigonal prismatic coordinated position Me1, as well as the octahedrally coordinated position Me3 are occupied only by Pb. Me2, also octahedrally coordinated, is dominated by Pb, whereas the octahedra situated at the edges of the octahedral layers (Me4 and Me5) are centered around mixed (Pb,Bi) positions, with almost equal occupancy. The octahedrally coordinated site Me3 was found to incorporate vacancies (), created by the substitution 3Pb 2+ → 2Bi 3+ +, which allows for the observed deviations from the ideal composition, Pb 6 Bi 2 S 9 . Selenium is preferentially ordered at the fivefold-coordinated anionic sites. Taking into account vacancies, as well as Se for S substitutions the structural formula of Ag-free heyrovskýite from Vulcano is Pb 5.82 Bi 2.12  0.06 S 8.70 Se 0.30 .Comparison with the Ag-bearing heyrovskýite structures shows that during the 2 Pb → Ag(Cu)+Bi substitution the increased content of Bi is incorporated preferentially in the Me5 site until 2/3 Bi occupancy and thereafter in the two central octahedrally coordinated sites (Me2 and Me3). Silver occupies exclusively marginal octahedrally coordinated Me4 site like in the other members of the lillianite homologous series. The observed crystal chemical characteristics of the Ag-free heyrovskýite are in accordance with a model suggested by Callegari and Boiocchi, which describes the monoclinic form, aschamalmite, as an ordered polymorph of Pb 6 Bi 2 S 9 , and heyrovskýite as a fully disordered polymorph of the same compound. Ag incorporation is expected to increase the Pb/Bi disorder and to stabilize the orthorhombic heyrovskýite form.

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Section: Experimental Methodssupporting

confidence: 74%

Structure refinement of Ag-free heyrovskyite from Vulcano (Aeolian Islands, Italy)

Pinto

Balić-Žunić

Garavelli

et al. 2011

American Mineralogist

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“…The volume of the bicapped prism in Ag-free lillianite (Pinto et al, 2006) is 55.4 Å 3 and the PbÀS distances to the capping S atoms are 3.42 Å . These values and the unit-cell parameters of Pinto's lillianite sample (Table 1) show some influences from traces of Se.…”

Section: The Lillianite Homologous Seriesmentioning

confidence: 99%

Lillianites and andorites: new life for the oldest homologous series of sulfosalts

Makovicky¹,

Topa²

2014

Mineral. mag.

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The current state of the lillianite homologous series is presented, with its two branches À the lillianite branch of the predominantly Pb-Bi-Ag sulfosalts and the andorite branch of predominantly Pb-Sb-Ag sulfosalts. Both the natural and synthetic members are discussed, especially from the structural and compositional point of view and the related, chemically distinct and structurally more complicated members of the series are described. A number of new published, or hitherto unpublished observations is given, together with fairly exhaustive tables of data. Relationships between the complex structures of different 'andorite' species and principal structural features of 'oversubstituted' As-Sb and Bi-Sb species are discussed. Contrary to many studies of this subject, synthetic phases form an integral part of the paper. It is concluded that research in this long-known homologous series still supplies new interesting phases, especially in the fields of synthetic products and in its andorite branch.

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“…This disparity may be ascribed to their structural differences; lillianite differs from heyrovskýite in terms of the width of PbS-like slabs and PbS/Bi 2 S 3 ratio (3:1 and 6:1, respectively). Recent single-crystal XRD studies show that in Ag-free lillianite, Pb and Bi are statistically distributed among the sole Me1 and Me2 sites, with almost the same occupancy, while Me3 is completely filled by Pb (Pinto et al 2006). Therefore, the different behaviors between Ag-free lillianite and heyrovskýite could be due to differences in the width of galena-like slabs or in the distribution of Pb and Bi within the slabs.…”

Section: Incommensurate Modulationsmentioning

confidence: 99%

“…Detailed structural investigations on natural Ag-and Cu-free lillianite and heyrovskýite have only been published in recent years (Borodaev et al 2001(Borodaev et al , 2003Pinto 2004;Pinto et al 2006;Balić-Žunić et al 2007). Each of these studies has been carried out on natural materials formed at Vulcano (Aeolian Islands, Italy), under high-temperature fumarole conditions.…”

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Transmission electron microscopy investigation of Ag-free lillianite and heyrovskyite from Vulcano, Aeolian Islands, Italy

Mitolo

Capitani

Garavelli

et al. 2011

American Mineralogist

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We present a transmission electron microscopy (TEM) investigation of lillianite (Pb 3 Bi 2 S 6 ) and heyrovskýite (Pb 6 Bi 2 S 9 ), from Vulcano, Aeolian Islands, Italy. The minerals investigated represent the only naturally occurring Ag-and Cu-free sulfosalts in the lillianite homologous series (LHS). Three methods (crushing, ion-milling, and ultramicrotomy) were used to prepare TEM specimens. Selected area electron diffraction (SAED) patterns and high-resolution TEM (HRTEM) images indicate wellordered crystals with only minor stacking faults and, more rarely, nanoscale intergrowths of lillianite and heyrovskýite. The latter were sometimes found to form an incommensurate structural modulation with an angle of ~29° relative to b* in the (hk0) plane and a wavelength of ~75 Å. This represents the first observation of such incommensurate modulations in heyrovskýite. Although considerable evidence points toward an artifact induced by the sample preparation technique (i.e., ion-milling), the possibility that the incommensurate modulation could be a primary feature of heyrovskýite itself cannot be completely ruled out. The modulation could derive from an ordering process of Pb and Bi cations over Me4 and Me5 sites within the PbS-like layer or from ordering of vacancies, naturally present or induced by Bi 2 S 3 sublimation during ion-milling.

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COMPARATIVE CRYSTAL-STRUCTURE STUDY OF Ag-FREE LILLIANITE AND GALENOBISMUTITE FROM VULCANO, AEOLIAN ISLANDS, ITALY

Abstract: The crystal structures of natural Ag-free lillianite of fumarolic origin from Vulcano,

Cited by 31 publications

References 26 publications

Structure refinement of Ag-free heyrovskyite from Vulcano (Aeolian Islands, Italy)

Structure refinement of Ag-free heyrovskyite from Vulcano (Aeolian Islands, Italy)

Lillianites and andorites: new life for the oldest homologous series of sulfosalts

Transmission electron microscopy investigation of Ag-free lillianite and heyrovskyite from Vulcano, Aeolian Islands, Italy

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