Edenharterite (TlPbAs3S6): a new mineral from Lengenbach, Binntal (Switzerland)

Abstract

The phase TlPbAs 3 S 6 , synthesized in the course of hydrothermal experiments by A. Edenharter (1982), was found as a natural mineral at the well known occurrence of Pb-Tl-Cu-Ag-As-sulphosalt minerals in Lengenbach, Binntal (Switzerland). It occurs in small cavities in Triassic dolomite, together with a large number of other As sulphosalt minerals such as hutchinsonite, hatchite, wallisite, lorandite, and abundant realgar and orpiment. Edenharterite forms euhedral lathlike crystals (less than 1 mm in size), mostly intergrown to aggregates up to 2-3 mm. Electron microprobe analysis yielded (mean of 3 analyses) : Tl 25.51, Pb 35.08, Sn 0.06, As 27.09, S 23.17, total 100.91 wt %. The simplified formula is close to TlPbAs 3 S 6 . The mineral is bright brown-black. In thin fragments it is red translucent and has a raspberry-red streak. Microhardness is 98 kg/mm 2 (10 g load), corresponding to a Mohs hardness of about 2 1/2-3, D calc =5.09 g/cm 3 . Single crystal studies gave an orthorhombic cell with a=15.465(3), b=47.507(8), c=5.843(2) A, V=4292 A 3 , space group Fdd2 and Z=16. The strongest lines in the X-ray powder pattern are (d obd , I obs , hkl) : 3.801 (100)(191); 3.389 (22)(1.11.1) : 2.901 (19)(3.11.1) : 2.767 (43)(4.12.0); 2.732 (41)(511); 2.656 (24)(3.13.1); 1.7905 (15)(8.10.0). The name is for Dr. Andcreas Edenharter (University of Gottingen) who first synthesized the phase TlPbAs 3 S 6 while conducting hydrothermal experiments with Tl-sulphosalts