Experiments with natural and synthetic hexagonal FeS + hexagonal Fe (sub 1-x) S assemblages indicate that FeS remains essentially stoichiometric in composition at all temperatures of heating, whereas the composition of co-existing hexagonal Fe (sub 1-x) S varies with temperature of heating as follows: at 25, 60, 105, 125, 140 degrees C its composition is 47.85, 48.17, 48.57, 49.18, 49.67 atomic % Fe, respectively. A comparison of the compositions of natural co-existing FeS and hexagonal Fe (sub 1-x) S with the compositions of these phases determined experimentally, suggests that the majority of the natural phases have attained equilibrium compositions at earth surface temperatures.Experiments involving hexagonal Fe (sub 1-x) S, monoclinic Fe (sub 1-x) S and pyrite indicate that monoclinic Fe (sub 1-x) S forms in charges containing <47.20 + or - 0.10 atomic % Fe heated at < or =304 + or - 6 degrees C. The anomalous behavior of monoclinic Fe (sub 1-x) S and the development of the non-equilibrium assemblage hexagonal Fe (sub 1-x) S + monoclinic Fe (sub 1-x) S + pyrite + vapor in charges heated at a variety of temperatures has led to the interpretation that monoclinic Fe (sub 1-x) S is metastable with respect to hexagonal Fe (sub 1-x) S + pyrite. The compositions of co-existing hexagonal Fe (sub 1-x) S and monoclinic Fe (sub 1-x) S at < or =304 + or - 6 degrees C are judged to be 47.20 + or - 0.10 and 46.75 + or - 0.05 atomic % Fe, respectively. The development of natural pyrrhotite assemblages in terms of the experimental results is briefly discussed.

First Page Preview

First page PDF preview
You do not currently have access to this article.