Structural relations and pseudosymmetries in the andorite homologous series

Abstract

The structure of quatrandorite is reported for the first time from an untwinned sample from Oura mine, San Jose, Bolivia. The mineral crystallizes in P2 1 /c, a = 19.1686 (19) Å, b = 17.160 (3) Å, c = 13.042 (2) Å, β = 90.008 (12)°, V = 4289.9 (11) Å 3 , Z = 4. Refinement to R obs = 5.66% was obtained with Jana2006. Quatrandorite belongs to the andorite series, whose members share two cell parameters while the third can be expressed as n × 4.3 Å, with n = 2, 4 and 6 for ramdohrite (uchucchacuaite, fizelyite), quatrandorite and senandorite, respectively. Both quatrandorite and senandorite are strongly pseudosymmetric up to Cmcm with one parameter corresponding to n = 1 (~ 4.3 Å). The hypothetical structure corresponding to Cmcm is also the aristotype common to both minerals. The strong structural similarity of quatrandorite and senandorite may explain their co -existence in some samples, which has in the past led to hypothesize the existence of a further member of the series, nakaséite, which was however later shown to consist of a random stacking of the two minerals. The Cmcm aristotype is not common to the n = 2 minerals (uchucchacuaite, ramdohrite, fizelyite), which are thus structurally less closely related to the two other members. A common aristotype to all three minerals can nevertheless be obtained via a different path, which leads to Cmme with the same cell parameters as Cmcm; the degree of pseudo -symmetry in this supergroup is however lower and there remain a difference in one sulfur position in this aristotype. It nevertheless confirms previous reports in the literature stating that the bulk of the structure of the minerals of this series can be reduced to a common principle, essentially a distorted galena; the departures from it are however crucial for the realization of the individual structures.

Modular Crystal Chemistry of Thallium Sulfosalts

“…This difference can be ascribed to the difference in the ratio of effective crystal radius of Tl to that of Sb and to As, respectively. bicapped coordination prism of lead in quatrandorite [60], 4 × 3.166 Å and 2 × 2.756 Å, with the two caps at 3.072 Å. This difference is an indication of problems which should occur with Tl inserted instead of Pb in the majority of homologues.…”

“…The coordination prism of thallium has bonds to prism corners from 3.042 Å to 3.443 Å and one of them to 3.531 Å, whereas the two caps have Tl-S distances of 3.334 Å and 3.558 Å. This can be compared to the simplified corresponding Pb-S distances in the bicapped coordination prism of lead in quatrandorite [60], 4 × 3.166 Å and 2 × 2.756 Å, with the two caps at 3.072 Å. This difference is an indication of problems which should occur with Tl inserted instead of Pb in the majority of homologues.…”

“…% Tl in rouxelite from Monte Arsiccio (Tuscany), in gross correlation Pb ↔ Tl + Sb. For this substitution, similarities in selected structural configurations of rouxelite to those in tsygankoite [60] may be important.…”

Oyonite, Ag3Mn2Pb4Sb7As4S24, a New Member of the Lillianite Homologous Series from the Uchucchacua Base-Metal Deposit, Oyon District, Peru

“…We decided to keep this non-standard setting of the space group to make easier the comparison with the other members of the lillianite homologous series [6]. The refined unit-cell parameters are a = 19.1806 (18), b = 12.7755 (14), c = 8.1789 (10) Å, β = 90.471 (11)…”

“…In ideal oyonite, n = 75. Following [6] and [10] [11] and menchettiite [4]), 6 (fizélyite [12]), 5 (ramdohrite [13]), 1 (quatrandorite [14]), 0 (senandorite [15]), −1 (andreadiniite [16]), −2 (arsenquatrandorite [17]), −3 (roshchinite [18]), and −5 (jasrouxite [19]). Oyonite, having an andorite component And 75 , corresponds to a new member in the sequence, having m = 4.…”