From Chalcogenides to Polychalcogenidehalides - First Identification in Mineral Samples

Mineral samples from the Prasolovskoe epithermal Au-Ag deposit, Russia, were investigated via transmission electron microscopy (TEM). One component was identified as the mineral kurilite Ag8Te3Se according to the data obtained from electron diffraction (ED) and Fourier transform analyses of high resolution micrographs. Micrometer-sized grains of kurilite were found next to other noble metal chalcogenide domains like the hessite-type. The EDX microprobe analyses of the kurilite domains were determined with the chemical composition Ag7.9Au0.1Te2.9Se1.0 which is consistent with kurilite doped by gold. Additionally noble metal polychalcogenidehalides (NMPH) were identified via ED. Monoclinic and tetragonal polymorphs of Ag5Te2Cl were observed for the first time in a mineral sample. One additional component, whose composition equates the kurilite-type component with regard to Ag, Au, Te, and Se but with a marginal chlorine component, crystallizes in a structure type known from synthetic NMPH, namely Ag23Te12X (X = Cl, Br). This phase as well as the phases Ag10Te4Br3 and Ag20Te10Br2 was found next to each other in an also investigated synthetic sample.