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Titolo: Rare Sulfosalts from Vulcano, Aeolian Island, Italy,. IV Lillianite
Data di pubblicazione: 2001
Citazione: Rare Sulfosalts from Vulcano, Aeolian Island, Italy,. IV Lillianite / Y.S.BORODAEV; A.GARAVELLI; C.GARBARINO; GRILLO S; N. MOZGOVA; T. UNSSPENSKAYA; F.VURRO. - 39(2001), pp. 1383-1396.
Abstract: Excellent samples of lillianite, a rare Pb-Bi sulfosalt, have found around a high-temperature fumarole at the La Fossa crater, Vulcano Island, Italy. The mineral is associated with cannizzarite and, subordinately, with galenobismutite and rare sulfosalts, as wel as sphalerite and selenian galena. Lillianite occurs as laths and fibers up to 100-130 /um in length, and about 20-30 and 1 /um in width, respectively. Electron-microprobe analyses show that the lillianite from Vulcano has a composition close to the ideal Pb3Bi2S6. Particularly interesting is the absence of Ag and Cu, which makes the lillianite from Vulcano unique in its putity, with minor incorporation of Cd. Like in other sulfosalts from Vulcano, significant Se concentrations are invariably present (1.38-2.22 wt. %). Traces of chlorine were found in some crystals due to the high Cl activity in the fumaroles, and are noted for first time. The general empirical formula,Pb3-x Bi2+2x/3(S6-y Sey)6, reflects the narrow composition field for the lillianite from Vulcano. The X-Ray powder-diffraction data, as well as microhardness and reflectance measurements, are given for distinct crystals with a different Pb/Bi value. The unit-cell constants are a=13.576(9), b=20.606(8), c=4.119(2) A for the crystal with Pb/Bi =1.50, and a=13.56(1), b=20.57(1), c=4.115(2) A for the one with Pb/Bi=1.41. In both films, h+l=2n reflections correspondto the space group Bbmm.The lower value of microhardness of the Bi-rich sample may reflect the less well-ordered structure and the effect of heterovalent substitution 3Pb2+ -> 2Bi3+ + vac.. A comparison between the lillianite from Vulcano and the synthetic homologous Phase III is also given.
Tipologia:1.1 Articolo in rivista

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