First occurrence of the <i>M2a2b2c</i> polytype of argentopolybasite, [Ag₆Sb₂S₇][Ag₁₀S₄]: Structural adjustments in the Cu-free member of the pearceite-polybasite group

Author(s)

Luca Bindi, Frank N. Keutsch, Dan Topa, Uwe Kolitsch, Marta Morana, Kimberly Tait

Abstract

The chemistry and the crystal structure of the recently described mineral argentopolybasite are critically discussed based on the study of two new occurrences of the mineral: Gowganda, Timiskaming District, Ontario, Canada and IXL Mine, Silver Mountain mining district, Alpine County, California. The crystal structure of argentopolybasite can be described as the sequence, along the c axis, of two alternating layers: a [Ag6Sb2S7]2- A layer and a [Ag10S4]2+ B layer. In the B layer there are linearly-coordinated metal positions (B sites), which are usually occupied by copper in all members of the pearceite-polybasite group, resulting in a B-layer composition [Ag9CuS4]2+. In argentopolybasite, however, Ag fills all the metal sites in both A and B layers. By means of a multi-regression analysis on 67 samples of the pearceite-polybasite group, which were studied by electron microprobe and single-crystal X-ray diffraction, the effect of Ag, Sb and Se on the B sites of the B layer was modelled. Although the nomenclature rules for these minerals are based on chemical data only, we think this approach is useful to evaluate the goodness of the refinement of the structure (Ag/Cu disorder) and thus fundamental to discriminate different members of the pearceite-polybasite group.

Organisation(s)

Department of Mineralogy and Crystallography

External organisation(s)

Naturhistorisches Museum Wien (NHM), University of Florence, Harvard University, Royal Ontario Museum

Journal

Mineralogical Magazine

Volume

87

Pages

561-567

No. of pages

7

ISSN

0026-461X

DOI

https://doi.org/10.1180/mgm.2023.30

Publication date

08-2023

Peer reviewed

Yes

Austrian Fields of Science 2012

105116 Mineralogy, 105113 Crystallography

Keywords

ASJC Scopus subject areas

Geochemistry and Petrology

Portal url

https://ucrisportal.univie.ac.at/en/publications/0760e8f5-997d-4705-9f7c-b81fda6d1c4c