Su blimates were sampled at the Fossa crater of VuIcano Island (Sicily, Italy) in June and October 199 1. Sampling was carried out by means of silica tubes inserted as deep as possible into those fumarolic vents around which lead and bismuth sulphides and sulphosalts occurred. The main mineralogical phases found within the silica tubes are native sulphur, ammonium tetrafluoroborate, lead and bismuth chlorides, oxychlorides, sulphochlorides, sulphides and sulphosalts. The lead and bismuth mineral assemblage is interpreted as the result of the transport of lead and bismuth as volatile chlorides. Microtextural and microanalytical studies (SEM + EDS) on chloro-sulphides and sulphosalts suggest that the latter were deposited from metastable chlorosulphides through reactions involving gaseous H2S. The absence of chlorosulphides on the ground confirms their metastability. The lack of sulphates in the mineralogical association sampled within the silica tubes is due to the reducing conditions of voIcanic fluids.

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

Wittite and cannizzarite, two rare and structurally related nonstoichiometric sulfosalts belonging to the system Pb-Bi-S-Se, were found together around high-temperature fumaroles at La Fossa crater, Vulcano island, Italy. This occurrence makes a comparative study by different methods possible (scanning electron microscope, electron microprobe, and X-ray and electron diffraction). We discuss once more the question whether or not they are distinct mineral species. Cannizzarite was found in samples collected from 1990 to 1995 in assemblages with bismuthinite and galenobismutite (mostly), in some cases with lillianite, heyrovskiite, Se-bearing galena, kirkiite, and the new species mozgovaite. Wittite was revealed only in samples collected in 1995 around the fumarole vent F11 in association with bismuthinite. Both minerals form aggregates of very tiny sheaves of slightly divergent, bladed crystals (cannizzarite up to 0.5 mm in length and 0.07 mm in width; wittite up to 2 mm in length). The electronmicroprobe data obtained (141 analyses) show significant variations in proportions of the main elements. In terms of Bi/(Bi + Pb), the range of composition is 3.14 at.%; the Se content varies from less than 1 to 14.65 wt%. The composition field of the minerals under consideration may be described by the general empirical chemical formula Pb 3+x Bi 4-x (S 9-y Se y) 9-x/2 or Pb 3 (Bi 4-x Pb x) 4 (S 9-y Se y) 9-x/2 , with 0.04 ≤ x ≤ 0.28, and 0.5 ≤ y ≤ 3.5. Electron-diffraction data and X-ray investigations of a sample of wittite containing ~8.5 wt% Se confirm that cannizzarite and wittite have the same structure. Measured unit-cell parameters show that volumes of the H and Q subcells both vary in direct proportion to Se content. No chemical discontinuity between cannizzarite and wittite series has been observed up to 40 at.% Se; consequently, wittite may be validated or discredited as a distinct mineral species only when a definitive crystallographic work will prove that Se exceeds S in the H layers.

Vurroite, ideally Pb 20 Sn 2 (Bi,As) 22 S 54 Cl 6, is a new mineral species from the modern Pb-Bi epithermal deposit of La Fossa crater, on Vulcano Island, Italy. It occurs as a volcanic encrustation deposited around high-temperature fumaroles (400-600°C) located both on the rim and on the inner slope of the active crater. The mineral consists of slender, needle-shaped crystals up to 0.4 mm long and 0.01 mm across, which generally form fibrous aggregates. Associated minerals are bismuthinite, lillianite, kirkiite, heyrovskýite, galena, and other less-well-characterized sulfochlorides of Pb(Bi), some of which contain traces of Tl, Sn or As. The color of vurroite is silver-gray, with a metallic luster. In reflected plane-polarized light, it is white, without distinct bireflectance or pleochroism. Anisotropism is weak, without color effects. The measured values of reflectance in air for a single grain are 34.25 (470 nm), 32.95 (546 nm), 32.60 (589 nm), 31.05% (650 nm); values for 400-800 nm are tabulated. Electronmicroprobe analyses yield the following ranges of concentrations (wt.%):