Crystal chemistry of sartorite homologues and related sulfosalts

Ten selected sartorite homologues (Pb-As sulfosalts) and related compounds (mainly Tl-Sb-As sulfosalts) were investigated on modular and polyhedral le vel. For the cations with active lone-electron pairs crystal chemical trend s could be established and correlated to the polyhedral settings by means o f the polyhedral parameters; polyhedral volume, volume of circumscribed sph ere, eccentricity, and volume distortion. For the As, Sb, and Pb coordinati ons, pairs of opposing bonds plotted into an xy-diagram form element specif ic hyperbolae. Besides the hyperbolic trend, a linear 'join' perpendicular to the median line of two hyperbola arms was found for As and Sb. This situ ation is regarded as the result of two superimposed but unresolved position s in the same coordination polyhedron, with partly opposing long and short bonds. The crankshaft chains (unbroken chains of short As-S and Sb-S bonds) in the investigated sartorite homologues and the related compounds are ori ented at right angles to each other in two adjacent planes within one tight ly bonded double layer. The exceptions are synthetic BaSb2Se4 and rathite I . This could explain the existence of the exsolution intergrowth of dufreno ysite and rathite I which otherwise fall on the same isopleth in the phase triangle Pb2S2 - (As,Sb)(2)S-3 - (Ag,Tl)(2)S.