Phase equilibria in the system MgO-MgF2-SiO2-H2O

The proportions of F and OH in synthetic talc, clinohumite, chondro-dite, norbergite, brucite, and sellaite have been determined by X-ray measurement of interplanar spacings. Unit cell refinement has been carried out on intermediate sellaite, approximate composition MgOHF. The compositions of coexisting phases have been determined in forty hydrothermal experiments yielding information on eighteen different chemical equilibria. These data, combined with phase equilibrium and calorimetric data from the literature, have been treated by the method of least squares to produce a thermodynamic model of the system. Computed equilibria based on the model are in good agreement with data on natural assemblages.Science, Faculty ofEarth, Ocean and Atmospheric Sciences, Department ofGraduat