Thermodynamic analysis of experimentally determined reactions among H2O and the nine minerals: antigorite, anthophyllite, brucite, chrysotile, enstatite, forsterite, periclase, quartz, and talc, shows that the available calorimetrically determined enthalpies and entropies are not compatible with the hydrothermal experiments. Major discrepancies appear to exist for the enthalpies of formation of talc and enstatite and for the entropy of anthophyllite. The experimental data, molar volumes and heat capacities are internally consistent, however, and permit only one topology of phase diagram for Mg-anthophyllite, that first proposed by Greenwood (1963). Our “best” set of thermodynamic parameters, internally consistent with these data, includes values for the enthalpy of formation from the elements (298 K, 1 bar) of antigorite and anthophyllite: −71435 kJ and −12073 kJ respectively.

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