Rare sulfosalts from vulcano, aeolian islands, Italy: VII. Cl-bearing Galenobismotite

TY - JOUR

T1 - Rare sulfosalts from vulcano, aeolian islands, Italy

T2 - VII. Cl-bearing Galenobismotite

AU - Pinto, Daniela

AU - Balic Zunic, Tonci

AU - Bonaccorsi, Elena

AU - Borodaev, Yuri S.

AU - Garavelli, Anna

AU - Garbarino, Carlo

AU - Makovicky, Emil

AU - Mozgova, Nadezhda N.

AU - Vurro, Filippo

PY - 2006

Y1 - 2006

N2 - Cl-bearing galenobismutite (Cl ranging from 0.12 to 1.45 wt.%), discovered among high-temperature fumarole incrustations at "La Fossa" crater (Vulcano Island, Italy), has been chemically and structurally investigated. The mineral is commonly associated with bismuthinite, cannizzarite, lillianite, heyrovskýite and galena; rarely with kirkiite, vurroite and some other less characterized Pb(Bi)-sulfochlorides. Electron-microprobe investigations show that Cl-bearing galenobismutite from Vulcano has a wide compositional field (Pb/Bi atomic ratio ranging from 0.52 to 0.72). The statistical analysis of chemical data shows correlations between the main elements and chlorine, positive Pb vs Cl and negative Bi vs Cl, according to the coupled heterovalent substitution scheme: Pb2+ + Cl- « Bi3+ + S2-. The compositional variation of Cl-bearing galenobismutite can be represented by the general empirical formula Pb1+xBi2-x(S4-x-yClxSey) with 0 < x < 0.3 and 0 < y < 0.2, indicating the extent of departure from the ideal composition PbBi2S4 toward an increase of the Pb content and a decrease of Bi. The phase IV, synthetic analogue of galenobismutite in the system Pb-Bi-S, has the compositional field extending from ideal composition toward decreasing Pb (Pb/Bi atomic ratio 0.50 - 0.39). It reflects another type of substitution: 3Pb2+ à 2Bi3+ + ¿. X-ray single crystal investigations were performed on two selected crystals of Cl-bearing galenobismutite from Vulcano. The composition of galenobismutite controls the a and b unit-cell parameters, which increase with the increase of the Cl content. The structural refinements converge to the agreement R values of 3.10 % for 840 reflections [Fo > 4s(Fo)] and 1.49 % for 376 reflections [Fo > 4s(Fo)], respectively. The structure of Cl-bearing galenobismutite is topologically identical to that of Cl-free galenobismutite. The excess of Pb observed in Cl-bearing galenobismutite is incorporated in the trigonal prismatic M2gb and M3gb sites. No Pb for Bi substitution was observed for the octahedral position M1gb. No evidence of a preferential distribution of Cl among the anion positions was observed.

AB - Cl-bearing galenobismutite (Cl ranging from 0.12 to 1.45 wt.%), discovered among high-temperature fumarole incrustations at "La Fossa" crater (Vulcano Island, Italy), has been chemically and structurally investigated. The mineral is commonly associated with bismuthinite, cannizzarite, lillianite, heyrovskýite and galena; rarely with kirkiite, vurroite and some other less characterized Pb(Bi)-sulfochlorides. Electron-microprobe investigations show that Cl-bearing galenobismutite from Vulcano has a wide compositional field (Pb/Bi atomic ratio ranging from 0.52 to 0.72). The statistical analysis of chemical data shows correlations between the main elements and chlorine, positive Pb vs Cl and negative Bi vs Cl, according to the coupled heterovalent substitution scheme: Pb2+ + Cl- « Bi3+ + S2-. The compositional variation of Cl-bearing galenobismutite can be represented by the general empirical formula Pb1+xBi2-x(S4-x-yClxSey) with 0 < x < 0.3 and 0 < y < 0.2, indicating the extent of departure from the ideal composition PbBi2S4 toward an increase of the Pb content and a decrease of Bi. The phase IV, synthetic analogue of galenobismutite in the system Pb-Bi-S, has the compositional field extending from ideal composition toward decreasing Pb (Pb/Bi atomic ratio 0.50 - 0.39). It reflects another type of substitution: 3Pb2+ à 2Bi3+ + ¿. X-ray single crystal investigations were performed on two selected crystals of Cl-bearing galenobismutite from Vulcano. The composition of galenobismutite controls the a and b unit-cell parameters, which increase with the increase of the Cl content. The structural refinements converge to the agreement R values of 3.10 % for 840 reflections [Fo > 4s(Fo)] and 1.49 % for 376 reflections [Fo > 4s(Fo)], respectively. The structure of Cl-bearing galenobismutite is topologically identical to that of Cl-free galenobismutite. The excess of Pb observed in Cl-bearing galenobismutite is incorporated in the trigonal prismatic M2gb and M3gb sites. No Pb for Bi substitution was observed for the octahedral position M1gb. No evidence of a preferential distribution of Cl among the anion positions was observed.

KW - Faculty of Science

KW - Italien

KW - vulkan ø

KW - krystal strukturer

KW - Cl-bearing galenobismutite

KW - Italy

KW - Vulcano Island

KW - fumaroles

KW - crystal structure

KW - Pb-Bi sulfosalt

U2 - 10.2113/gscanmin.44.2.443

DO - 10.2113/gscanmin.44.2.443

M3 - Journal article

SN - 0008-4476

VL - 44

SP - 443

EP - 457

JO - Canadian Mineralogist

JF - Canadian Mineralogist

ER -