Gold-silver sulfoselenides of AgAu(Se,S) series-AgAuSeS, AgAuSeS, and AgAuSeS-have been synthesized by fusing the elements in the required stoichiometric amounts in evacuated quartz ampoules. The single crystal X-ray diffraction data indicate the existence of two solid-solution series: petzite-type cubic AgAuSe-AgAuSeS (space group I432) and trigonal AgAuSeS-AgAuS (space group $$ R\overline{3} c $$). Both crystal structures differ in the distribution of Ag/Au cations in the same distorted body-centered cubic sublattice of chalcogen anions. The morphotropic transformation results from the shrinkage of anion packing accompanied by the shortening of Ag-Ag distances. The structure of uytenbogaardtite mineral, earlier incorrectly interpreted as a tetragonal or cubic cell, is similar to that of the trigonal AgAuS end-member. [ABSTRACT FROM AUTHOR]