Publication details
The crystal structure of Tl2.36Sb5.98As4.59S17, the lead-free endmember of the chabournéite homeotypic group
| Authors | |
|---|---|
| Year of publication | 2021 |
| Type | Article in Periodical |
| Magazine / Source | Canadian Mineralogist |
| MU Faculty or unit | |
| Citation | |
| Web | https://pubs.geoscienceworld.org/canmin/article/59/3/533/606476/The-crystal-structure-of-Tl2-36Sb5-98As4-59S17-the |
| Doi | http://dx.doi.org/10.3749/canmin.2000093 |
| Keywords | chabourneite; sulfosalt; homeotypic group; endmember; Vorontsovskoe gold deposit |
| Description | The crystal structure of Tl2.36Sb5.98As4.59S17, the lead-free endmember of the chabourneite homeotypic group, from the Tl-As-Sb-rich gold deposit at Vorontsovskoye (the Urals, Russia) was determined and refined to R(obs) 0.099 for 9340 unique observed X-ray reflections. The triclinic unit-cell parameters determined from single-crystal data are as follows: alpha = 8.63253(19) angstrom, b= 16.3055(7) angstrom, c= 21.8196(8) angstrom, alpha = 75.094 (3)degrees, beta = 83.631(2)degrees, gamma = 89.303 (2)degrees, V= 2949.18(18) angstrom(3) (Z= 4), space group P (1) over bar. The crystal structure is composed of (001) slabs based on PbS and SnS archetypes, arranged in regular alternation. All Sb(As) coordination polyhedra are (Sb,As)S3+2+(1 or 2) coordination pyramids, in the majority of cases with a mixed Sb-As occupancy in both slab types. Bond-length distributions were studied in detail. The zig-zag boundary between the slabs is composed of a repeating sequence of [100] Tl-Tl, Sb-Sb (1/3 substituted by As), Tl-Tl, and Tl-Sb columns. Thallium forms tricapped trigonal coordination prisms and (Sb,As) forms bicapped prisms. Differences compared to two related structures-parapierrotite and tsygankoite-are specified. Twinning of chabourneite is connected with the (imperfect) order-disorder character of the structure, which is connected with the configurations observed on slab boundaries. The structure refinement of the lead-free Tl-(Sb,As) chabourneite endmember presented in this paper is the best starting point for a restudy of all complexities of the chabourneite homeotypic group. |