The influence of Fe on the reaction clinochlore + kyanite ó magnesiochloritoid + talc (1) was determined experimentally as a function of pressure (1.6 - 2.6 GPa) and composition at 600 and 540oC. Analytical electron microscopy (AEM) was used to determine the compositions of the coexisting phases in these complex multiphase run products. Within the compositional range studied (xFebulk = 0.12 0.34) chlorite solid solutions were always richer in magnesium than the coexisting chloritoid solid solutions. Fractionation of Fe into the chloritoid extends the stability field of the assemblage chloritoid plus talc towards lower pressures. However, the extent of the stability field for increasing xFe is less than one would expect for ideal mixing behaviour in chloritoid and chlorite and indicates a moderate, positive deviation from ideality for chloritoid solid solutions. The thermodynamic data for magnesiochloritoid given in Simon et al. (1997) and in Vidal et al. (1999) are in good agreement with the present experiments, those of Holland & Powell (1998) yield pressures much too high at least compared with the experiments at 600 oC.

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Koch-Müller, M.; Wirth, R. (2001): An experimental study of the effect of iron on magnesiochloritoid-talc-clinochlore-kyanite stability. Contributions to Mineralogy and Petrology, 141, 5, 546-559.