Abstract

In order to evaluate the effects of Te-for-S substitution in the minerals of the argyrodite group, the crystal structure and chemical composition of a crystal of Te-rich canfieldite from the Lengenbach quarry, Binntal, Switzerland, was investigated. The unit-cell parameters are a 11.0003(6) Å and V 1331.1(1) Å3. The structure was solved and refined in the space group F4̅3m to R1 = 0.0308 for 194 independent reflections and 21 parameters. Quantitative analysis led to the chemical formula Ag8.05(Sn1.03Ge0.01)∑1.04(S3.95Te1.95Se0.01)∑5.91, ideally Ag8Sn(S,Te)6. The crystal structure of Te-rich canfieldite was found to be topologically identical to that of putzite, (Cu4.7Ag3.3)GeS6. Neglecting the short Ag-Ag contacts (due to disorder), the two Ag atoms in the structure can be considered as three-fold (Ag1) and four-fold (Ag2) coordinated. Tin adopts a regular tetrahedral coordination. The refinement of the site-occupancy factor indicates Te to be disordered over the three anion positions (i.e., X1, X2, and X3), with a preference for the X1 site.

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