Journal of Petrology

Thermodynamic Mixing Models for Muscovite-Paragonite Solutions Based on Solution Calorimetric and Phase Equilibrium Data.

Jacques Roux, Guy L. Hovis

ABSTRACT

Enthalpies of solution have been measured on a series of muscovite-paragonite micas in 20.1% HF at 50 degrees C under isoperibolic conditions. The molar enthalpy of formation of paragonite at 298 K, for which no calorimetrically measured value is currently available, has been determined to be -5937.5 (plus or minus 3) kJ. An inversion of all calorimetric, volumetric and phase equilibrium data has been performed, giving a range of mixing properties of 2M1 micas for enthalpy (Hex) and volume (Vex) at pressures up to 10 kbar, forcing excess entropy (Sex) to be zero and using a subregular mixing model are favored:

Hex (kJ) = (10.6 + 4.45 (1 - 2Xms)) Xms (1 - Xms)

Vex (J/bar) = 0.452 Xms (1 - Xms)

However mixing models of higher order with asymetric negative Sex are also possible.

Keywords

muscovite;paragonite;solvus;calorimetry;solid-solution

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