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Activity-composition relationships for pyrope-grossular garnet

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Activity coefficients (γ) for grossular in pyrope-grossular garnet have been determined experimentally using the divariant assemblage garnet-anorthite-sillimanite (kyanite)-quartz. Values of γ for garnets with 10–12 mole % grossular have been obtained at 1000 °, 1100 °, 1200 ° and 1300 ° C at pressures between 15 and 21 Kb. The data are consistent with a symmetrical regular solid model for grossular-pyrope solid solutions. The interaction parameter (W) increases linearly with decreasing temperature and is given by W = 7460-4.3 T cals (T in °K). A solvus in the pyrope-grossular solid solution is predicted with a temperature of critical mixing of 629°C±90 ° C.

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Hensen, B.J., Schmid, R. & Wood, B.J. Activity-composition relationships for pyrope-grossular garnet. Contr. Mineral. and Petrol. 51, 161–166 (1975).

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