On cooperite, braggite, and vysotskite

Detailed mineralogical analyses of cooperite, braggite, and vysotskite, together with phase equilibrium studies, reveal that, though there is no uncertainty regarding the identity of cooperite (PtS;P42/ mmc), one may consider braggite (Pt,Pd)S and vysotskite PdS to be nickeloan members of an isomorphous solid-solution series (Pd,Pt)S (P42/m). The results also suggest that this solid-solution series (braggite series) may be subdivided by restricting the name vysotskite to those members with less than about 10 mole percent PtS. Cooperite and braggite can both form at magmatic temperatures of IOOO°Cor above, but vysotskite is only formed at submagmatic temperatures, possibly by crystallization from a residual immiscible sulfide-rich melt or by solid-state reaction.