Lead-antimony sulfosalts from Tuscany (Italy). III. Pillaite, Pb₉Sb₁₀S₂₃ClO_0.5, a new Pb-Sb oxy-chloro-sulfosalt, from Buca della Vena mine

Authors: Orlandi, Paolo; Moëlo, Yves; Meerschaut, Alain; Palvadeau, Pierre

Source: European Journal of Mineralogy, Volume 13, Number 3, 1 May 2001 , pp. 605-610(6)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

The new mineral pillaite, Pb₉Sb₁₀S₂₃ClO_0.5, an oxy-chloro-sulfosalt, has been found at Buca della Vena mine in the Apuan Alps, northern Tuscany, Italy. It crystallized in small fractures of dolomitic lenses in massive FeBa ore, together with many Pb-Sb sulfosalts, among which the oxy-sulfosalt scainiite. Pillaite occurs as black acicular crystals with metallic lustre, elongated // [010], up to 1 cm long and less than 0.1 mm thick. The mineral is brittle, opaque; VHN₅₀ =175 kg/mm², d_calc =5.77 g/cm³. In reflected light it shows a weak anisotropy and bireflectance, and rare red internal reflections. Electron-microprobe analysis (wt. %): Pb 49.07, Sb 30.36, Cu 0.16, S18.73, Cl 0.98, O (crystal structure) 0.21, Sum 99.51. Empirical formula: Pb_9.30Sb_9.80Cu_0.10S_22.94Cl_1.06O_0.5; ideally: Pb₉Sb₁₀S₂₃ClO_0.5. Pillaite is monoclinic, space group C2/m, a = 49.65(3) Å; b = 4.150(4) Å; c = 21.91(1) Å; beta

=99.76(5)°; V =4449(10) Å3; Z = 4. The strongest lines of the X-ray powder diffraction pattern are (d (Å), I_obs, hkl): 4.14 (27) (205), 3.88 (20) (1201), 3.621 (26) (406, 1202), 3.548 (40) (1204, 1005), 3.480 (100) (206), 3.249 (24) (1205), 2.956 (47) (515, 1601, 1206, 514), 2.780 (22) (1310, 515). Pillaite belongs to the zinkenite group. Like for dadsonite and other chloro-sulfides, the formation of this mineral is related to a high chlorinity of the hydrothermal solution, but also to the oxygen fugacity, as for scainiite.

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Keywords: PILLAITE; NEW MINERAL; SULFOSALT; LEAD; ANTIMONY; OXY-CHLORO-SULFIDE; TUSCANY; ITALY

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0935-1221/2001/0013-0605

Publication date: 2001-05-01

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