Lead-antimony sulfosalts from Tuscany (Italy). IV. Crystal structure of pillaite, Pb₉Sb₁₀S₂₃ClO_0.5, an expanded monoclinic derivative of hexagonal Bi(Bi₂S₃)₉I₃, from the zinkenite group

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

Source: European Journal of Mineralogy, Volume 13, Number 4, 1 July 2001 , pp. 779-790(12)

Publisher: E. Schweizerbart'sche Verlagsbuchhandlung

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Abstract:

The crystal structure of pillaite, a recently described Pb-Sb oxy-chloro-sulfosalt from the Buca della Vena mine, Tuscany (Italy), was solved and refined to a residual R of 0.045 in the monoclinic system, with space group C2/m, and a = 49.49(1), b = 4.1259(8), c = 21.828(4) Å, β = 99.62(3)°, V = 4394(2) Å³. The structural formula is Pb_9.16Sb_9.84S₂₃ClO_0.5, corresponding to the electron-microprobe one Cu_0.10Pb_9.16Sb_9.84S_22.94Cl_1.06O_0.5 (ideally Pb₉Sb₁₀S₂₃ClO_0.5), with Z = 4 and D_calc. = 5.87. The crystal structure is organized around pseudo-threefold axes where chlorine atoms are in a trigonal prismatic coordination with Pb atoms. An oxygen position, half-filled, is bonded to two Sb atoms, like in scainiite. Pairs of pseudo-trigonal rods parallel to the elongation b-direction are connected along [102] to form rod-layers. The pillaite structure is an expanded homologue of hexagonal Bi(Bi₂S₃)₉I₃. Among lead sulfosalts, it belongs to the zinkenite group of cyclically twinned structures. Pillaite is the first example of a Pb-Sb sulfosalt where small amounts of two anion species simultaneously play a specific crystal chemical role, which is essential for the stabilization of the crystal structure: chlorine, like in dadsonite, and oxygen, like in scainiite.

Keywords: PILLAITE; CRYSTAL STRUCTURE; LEAD; ANTIMONY; OXY-CHLORO-SULFIDE; SULFOSALT; ZINKENITE GROUP

Document Type: Research article

DOI: http://dx.doi.org/10.1127/0935-1221/2001/0013-0779

Publication date: 2001-07-01

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