THE CRYSTAL STRUCTURE OF SULFOSALTS WITH THE BOXWORK ARCHITECTURE AND THEIR NEW REPRESENTATIVE, Pb15-2xSb14+2xS36Ox

Abstract

The new monoclinic phase with a structure-determined formula Pb 15−2 x Sb 14+2 x S 36 O x (Z = 4) was found only as a single grain in a micro-intergrowth of sulfosalts in the Klacianka Sb deposit, Low Tatra Mountains, Slovakia. Unit-cell dimensions are a 48.293(15), b 4.1107(13), c 34.223(11) A, β 106.168(5)°, space group C 2 /m. There are 11 independent lead sites, 13 antimony sites, and five mixed (Pb, Sb) sites, 36 sulfur positions, and a single, approximately half-occupied oxygen site. Some coordination polyhedra of antimony exhibit split Sb sites, with positional parameters refined independently. Because of the intergrowth, the final R 1 value remained at 23.5%. It does not reflect visibly upon positional parameters, but has an adverse influence on the occupancy of mixed positions. Until further occurrences are documented, it remains an unnamed mineral. It is a typical sulfosalt representative of the category of boxwork structures. Other structures of this category comprise pellouxite, marrucciite, vurroite, neyite, and several synthetic sulfosalts. Sulfosalts with a boxwork structure are formed by a combination of three types of structural modules: continuous walls with a complex structure of rod-layer type; these walls are interconnected by partitions, and the resulting boxlike channels are filled by another type of structure rods. In its entirety, this group demonstrates a number of types for each of these kinds of module. The “core” group of Pb–Sb sulfosalts, scainiite, pillaite, pellouxite, rouxelite, a synthetic Mn–Pb sulfosalt, and Pb 15−2 x Sb 14+2 x S 36 O x described in this study, depend on the presence of minor amounts of oxygen in the structures. Oxygen forms a part of a kermesite-like configuration that generates a pronounced change of the local structural arrangement and, in this way, makes the boxwork framework possible. Several REE sulfides form boxwork structures as well.