Startseite Another step toward understanding the true nature of sartorite: Determination and refinement of a ninefold superstructure
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Another step toward understanding the true nature of sartorite: Determination and refinement of a ninefold superstructure

  • Peter Berlepsch EMAIL logo , Thomas Armbruster , Emil Makovicky und Dan Topa
Veröffentlicht/Copyright: 31. März 2015
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Abstract

Single-crystal X-ray diffraction data, collected from a sartorite crystal from Lengenbach (Binntal, Valais, Switzerland), yielded a ninefold superstructure: space group P21/c; a = 37.71(2), b = 7.898(3), c = 20.106(8) Å, β = 101.993(7)°; R1 = 6.08% for 6293 reflections with I > 2σI. The sample is an N1,2 = 3,3 sartorite homologue and the refined formula Pb8Tl1.5As17.5S35 compares very well with the empirical formula Pb8.2Tl1.4As17.5Sb0.5S35 obtained from electron microprobe analyses. It has a high Tl content, up to 6.5 wt%. In a coupled substitution approximately 1.5 Tl+ replace about 0.5 As3+ and 1 PbS. The refined structure has 35 S atoms pfu instead of the expected 36 S (= 9 × 4 S, from PbAs2S4). The incorporation of substantial amounts of Tl+ into PbAs2S4 is essential for the type and periodicity of superstructures in sartorite. The refined superstructure can be interpreted as a socalled “lock-in” structure with a composition that yields a commensurate lattice for a mineral that usually has an incommensurate lattice. No commensurate periodicity could be found for a second crystal with about 0.5 Tl apfu.

Received: 2002-5-22
Accepted: 2002-7-25
Published Online: 2015-3-31
Published in Print: 2003-2-1

© 2015 by Walter de Gruyter Berlin/Boston

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