• journal_title：European Journal of Mineralogy
• Contributor：Alain MEERSCHAUT ; Pierre PALVADEAU ; Yves MOËLO ; Paolo ORLANDI
• Publisher：E. Schweizerbart'sche Verlagsbuchhandlung Science Publishers
• Date：2001-
• Format：text/html
• Language：en
• Identifier：10.1127/0935-1221/2001/0013-0779
• journal_abbrev：Eur J Mineral
• issn：0935-1221
• volume：13
• issue：4
• firstpage：779
• section：Articles

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)⁰, 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_cale. = 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 [102̄] 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.