Écrinsite, AgTl₃Pb₄As₁₁Sb₉S₃₆, a new thallium-rich homeotype of baumhauerite from the Jas Roux sulphosalt deposit, Parc national des Écrins, Hautes-Alpes, France

Autor(en)

Dan Topa, Uwe Kolitsch, Emil Makovicky, Chris Stanley

Abstrakt

Écrinsite, ideally AgTl3Pb4As11Sb9S36, is a new thallium sulphosalt species found in the Jas Roux As-Sb-Pb-Tl-Hg-Ag deposit, Parc national des Écrins, Département des Hautes-Alpes, France. Associated minerals in four different samples are jasrouxite, stibnite, smithite,guettardite, chabournéite, pierrotiteandAs-bearingzinkenite.Écrinsite isopaquewithmetallic lustre. It is brittle without any discernible cleavage and with conchoidal fracture. In reflected light écrinsite is white, pleochroism is not discernible. Internal reflections are absent. In crossed polarisers, anisotropism is distinct, with rotation tints in shades of grey. The reflectance data (%, air) are: 37.3, 38.6 at 470 nm,35.2, 36.7 at 546nm, 34.0, 35.5 at 589nmand 32.0, 33.3 at 650 nm.Mohs hardness is 3-3½, microhardnessVHN25 is in the range 175-201, with a mean value of 189 kgmm2. Average results of 20 electron-microprobe analyses for the structurally investigated grain are (inwt%):Ag2.03(10), Cu0.02(1), Tl 14.57(20), Pb 16.23(32), Sb 23.97(25), As 17.87(17), S 25.20(15), total 99.88 (15), corresponding to Ag0.87Cu0.02Tl3.28Pb3.61Sb9.06As10.98S36.19 (on the basis of 28Meþ36S = 64 apfu). The simplified formula, AgTl3Pb4Sb9As11S36, is in accordance with the results of the crystal-structure analysis and may be derived from the ideal baumhauerite formula, Pb12As16S36, by substitution of Sb for As and [(Tl,Ag)þþ(As,Sb)3þ]?2Pb2þ. The density, 4.96 g cm3, was calculated using the ideal formula. Écrinsite has a triclinic cell, space group P1, with a = 8.080(2), b = 8.533(2), c = 22.613(4)A , a = 90.23(3)°, b = 97.17 (3)°, g = 90.83(3)°, V = 1546.7(6)A 3, andZ = 1. The strongest five lines in the (calculated) powder-diffraction pattern are [d inA (I)(h k l)]: 4:14ð68Þð10 5Þ, 3.72(92)(1 0 5), 3:56ð100Þð1 06Þ; 3:53ð80Þð1 2 2Þ and 3.48(72)(1 2 2). Écrinsite is a new member of the sartorite homologous series with N1,2=3, 4, i.e., N = 3.5. Four other members share the same N value as écrinsite: baumhauerite, argentobaumhauerite, boscardinite and bernarlottiite. By comparison to the closely related boscardinite (ideally Tl2Pb8Sb14As4S36), écrinsite is characterised by both an excess of As over Sb and a distinctly higher substitution of [(Tl,Ag)þþ(As,Sb)3þ]?2Pb2þ. Baumhauerite and bernarlottiite are basically unsubstituted members, whereas argentobaumhauerite has a Ag substitution, without Tl.

Organisation(en)

Institut für Mineralogie und Kristallographie

Externe Organisation(en)

University of Copenhagen, Naturhistorisches Museum Wien (NHM), Natural History Museum London

Journal

European Journal of Mineralogy: an international journal of mineralogy, geochemistry and related sciences

Band

29

Seiten

689-700

Anzahl der Seiten

12

ISSN

0935-1221

DOI

https://doi.org/10.1127/ejm/2017/0029-2639

Publikationsdatum

05-2017

Peer-reviewed

Ja

ÖFOS 2012

105116 Mineralogie, 105113 Kristallographie

Schlagwörter

ASJC Scopus Sachgebiete

Geochemistry and Petrology

Link zum Portal

https://ucrisportal.univie.ac.at/de/publications/030e7bd5-e937-4257-9541-225884025bb8