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Jentschite (TIPbAs2SbS6) – a new sulphosalt mineral from Lengenbach, Binntal (Switzerland)

Published online by Cambridge University Press:  05 July 2018

Stefan Graeser  and
Andreas Edenharter
Stefan Graeser
Affiliation:
Natural History Museum CH-4001 Basel and Mineralogical Institute, University of Basel, CH-4056 Basel, Switzerland
Andreas Edenharter
Affiliation:
Institut für Mineralogie und Kristallographie, Universität Göttingen, D-37077 Göttingen, Germany
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Abstract

Jentschite, TlPbAs2SbS6, is a new sulphosalt mineral from the famous Lengenbach locality (Binntal, Switzerland). It was discovered in association with numerous other Tl-As-sulphosalts such as hutchinsonite, wallisite-hatchite, edenharterite, bernardite, abundant realgar and orpiment in small cavities in a dolomitic rock of Triassic age which forms part of the Penninic Monte-Leone-nappe. The first specimens consisted of extremely small polysynthetically twinned crystals; a later find yielded less complicated twinned crystals in sizes up to 2 mm length. Single crystal X-ray diffraction studies gave a monoclinic cell with a = 8.121(3), b = 23.969(9), c = 5.847(3) Å, β = 107.68(3)° V = 1084.3(5) Å3, Z = 4, space group P21/n. The strongest lines in the X-ray powder diagram are (dobs in Å, Iobs, hkl): 2.823 (100)(116), 3.587 (86)(221), 2.778 (84)(260), 3.998 (74)(060), 2.670 (58)(301), 3.816 (54)(210). Chemical composition (electron microprobe, mean of 15 analyses, wt.%) is: Tl 23.92, Pb 21.44, As 19.16, Sb 12.53, S 22.42, total 99.47 wt.% from which a simplified formula TlPbAs2Sb1S6 can be derived. This formula is very close to that of the (orthorhombic) mineral edenharterite TlPbAs3S6. From structural and chemical data it was interpreted as the ordered structure of an Sb-bearing relative of edenharterite, a postulation that meanwhile could be confirmed by the complete structure determinations of both, edenharterite and jentschite (Berlepsch, 1996). Jentschite occurs in prismatic crystals up to 2 mm length; it is opaque with a black metallic to submetallic luster, red translucent in thin fragments. Fracture is uneven to conchoidal, the mineral is extremely brittle, the cleavage along (01) is perfect; the streak is dark red (darker than that of edenharterite). Mohs hardness is 2–2½, according to a microhardness VHN (10 g load) of 38–51 kg/mm2. The calculated density yields Dcalc = 5.24 g/cm3.

The name is for Franz Jentsch (1868–1908) from Binn, a local ‘Strahler’ and for several years head of an early Lengenbach syndicate that exploited the rare Lengenbach sulphosalt minerals at the beginning of this century.

Keywords

jentschiteT1-Pb-As-Sb-sulphosaltnew mineralcrystal datamicroprobe analysesLengenbachSwitzerland
Type
Mineralogy
Information
Mineralogical Magazine , Volume 61 , Issue 404 , February 1997 , pp. 131 - 137
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1997

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References

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