Auger and X-ray photoelectron spectroscopies were used to study crystals of stoichiometric pyrrhotite produced in the system Fe–S–CdS–NH4Cl–H2O under hydrothermal conditions at 450 °C and 1 kbar. The results obtained were compared with data of thermal atomic absorption analysis of Cd species. Under the growth of pyrrhotite crystals in the presence of Cd, one or two adsorbed species of Cd form, depending on its concentration. Both species are fine-film surface phases. One species is a compound of cadmium with oxygen and sulfur (and, possibly, chlorine), and the other is a nonautonomous sulfide-like phase that forms prior to the bulk phase (CdS). The incorporation of trace elements into the surface films might be a universal mechanism of uptake of incompatible elements by minerals, especially at elevated temperatures and pressures. It is shown that the combination of surface spectroscopy and thermal atomic absorption analysis opens up new avenues for studying adsorbed species of trace elements. This combination is useful in the ambiguous cases when the chemical shifts are small and in studying compatible elements for which isomorphous uptake prevails adsorption.

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