Suredaite, PbSnS₃, a new mineral species, from the Pirquitas Ag-Sn deposit, NW-Argentina: mineralogy and crystal structure

Abstract

Suredaite, ideally PbSnS 3 , is a new mineral species from the Pirquitas Ag-Sn deposit (Province Jujuy, NW-Argentina). It was observed in symmetrically banded veins in the Oploca district, and is associated with sphalerite, arsenopyrite, pyrite-marcasite, cassiterite, cylindrite, franckeite, hocartite, rhodostannite, and various Ag-Sb and Ag-Bi sulfosalts in minor amounts. Suredaite occurs in layers up to 1 cm in thickness as aggregates of radially arranged tabular-prismatic (single) crystals, has a metallic lustre, and a dark grey streak. VHN 50 ranges between 18.2 and 20.6 (mean 19.6) GPa, the Mohs hardness is 2.5-3. It has perfect cleavages parallel to {001}, {101}, and {100}. The measured density varies between 5.54 and 5.88 g/cm 3 , D x was determined to be 5.615 g/cm 3 . In reflected plane-polarised light, it is white and is not perceptibly bireflectant or pleochroic. It lacks internal reflections and is weakly anisotropic with metallic blue, mauve to brown rotation tints. Specular reflectance percentages in air and in oil are tabulated from 400 to 700 nm and compared graphically with those for the type specimen of teallite, PbSnS 2 . Electron microprobe analyses showed suredaite to be chemically inhomogeneous with respect to the compositional variations (in wt%): Pb 42.3-48.5, Ag 0.3-1.1, Fe 0.3-1.0, As 0.2-2.1, Sn 27.7-30.2, S 23.1-24.7. The crystal structure determined from single-crystal X-ray diffraction data revealed orthorhombic symmetry [space group Pnma, Z = 4, a = 8.8221(3), b = 3.7728(3), c = 14.0076(3) Å; V = 466.23(4) Å 3 ]. The atomic arrangement is isostructural to the NH 4 CdCl 3 structure type which exists in a series of isotypic sulfides and selenide compounds. The suredaite structure, which is the natural analogue of synthetic PbSnS 3 , consists of columns of double-edge sharing octahedra running parallel to the b axis, which house the Sn atoms. These columns are linked by rods of eightfold-coordinated Pb atoms. On the basis of the structure determination, the empirically determined idealized formula follows a [8] (Pb, As,Ag, Sn) [6] (Sn,Fe)S 3 stoichiometry. Crystalchemical arguments suggest Ag possibly to occupy interstitial sites according to the alternative formula [4] (s,Ag) [8] (Pb, As, Sn) [6] (Sn,Fe) S 3 . The name of this new mineral species is in honor of R.J. Sureda Leston, head of the

Electronic and Vibrational Properties of Pbsns3

“…There are four formula units in the unit cell; this gives a total of 20 atoms in five types. The fractional coordinates used in this study were adopted from Paar et al [3] and are listed in Table 1. Fig.…”

“…Fig. 1 shows the structure of PbSnS 3 In the band structure calculations, we have utilized the local density approximation with the norm-conserving 6 pseudopotential method within the framework of the density functional theory as implemented in the Abinit package [7,8]. For exchange and correlation, the parametrization of Perdew and Zunger [9] was used.…”

“…It is a relatively new mineral species, as a result, not much study has been done on it. However, a number of experimental studies have been done [3,4,5] which put the electronic band gap value at 1.04 eV. To the best of our knowledge, this is the first time a theoretical investigation will be carried out on LTS.…”

“…It belongs to a group of semiconductors of the general formula A II B IV S 3 and it is found in nature in tin ore [3]. Suredaite as is also known occurs: (1) as layers up to 1 cm thickness which are composed of tabular prismatic crystals, elongated along [010] and inter-grown in fan-shaped arrangements, and (2) as individual needle-like crystals, embedded in sphalerite.…”

Coiraite, (Pb,Sn2+)12.5As3Fe2+Sn4+5S28: a franckeite-type new mineral species from Jujuy Province, NW Argentina

“…Several years later, detailed mapping by the first author was undertaken in the Oploca sector of this deposit. In one of the drifts, a vein was exposed which was initially named 'suredaite vein' (Paar et al, 2000) and subsequently 'Veta Oploca Norte', the 'northern Oploca vein' (Paar et al, 2001). This vein attracted our interest because of a well developed banded texture with mineralogy very similar to that of the hand specimens obtained in 1997.…”