gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1983.047.345.04 Thermodynamic Mixing Properties of Pyrrhotine, Fe1−XS Powell Roger Department of Earth Sciences, University of Leeds, Leeds LS2 9JT 12 1983 47 345 437 440 6 7 1983 Copyright © 1983, The Mineralogical Society 1983 Abstract

Published data from pyrrhotine-vapour equilibrium experiments are used to make inferences concerning the high-temperature thermodynamic mixing properties of pyrrhotine. Darken's quadratic formalism provides the justification for plotting activity of sulphur data against (1−X)2, where X is used in Fe1−XS to express the composition of non-stoichiometric pyrrhotine. Such plots show that the thermodynamic behaviour of pyrrhotine appears to be different on either side of X = 0.125, the Fe7S8 composition.