The Canadian Mineralogist

Phase relations in the condensed system Fe–Os–S were investigated by means of dry syntheses from the elements at 1180°, 1100 ° and 900°C. The Fe-rich sulfide melt dissolves only traces of Os. Fe1–xS dissolves up to 0.7 at. % Os at 1180°C; Os solubility decreases to 0.3 at. % at 900°C. The S-rich sulfide melt dissolves up to 0.5 at. % Os at 1180°C. The principal Fe–Os alloys at all temperatures studied are cubic (Fe,Os), rhombohedral (Os,Fe) and nearly pure Os. The bulk of Fe–Os alloys coexist with Fe-rich sulfide melt and S-poor Fe1–xS; we provide Nernst partition coefficients for Os. The three-phase association alloy – Fe1–xS – OsS2 involves alloys with less than 1 at. % Fe. The solubility of Fe in OsS2 increases with decreasing temperature and increasing fugacity of sulfur, possibly making analyses of erlichmanite for trace quantities of Fe important