Stability of grandite garnet in H2O-CO2 mixtures at 600.DEG.C under 100 MPa.

With a fluid pressure of 100 MPa, grandite garnets with various Fe/(Fe+Al) ratios have been synthesized hydro thermally from the mixtures of reagent grade of CaO, CaCO3, Al2O3, Fe2O3 and SiO2. Grossular is formed at the CO2 mole fraction below 0.03, while the assemblage calcite-wollastonite-anorthite becomes stable above the value. An isobaric, isothermal eutectoid point appears in the system Ca3Al2Si3O12–Ca3Fe2Si3O12–CO2. The point seems to be located approximately at 90 mole % in the andradite molecule, and 0.8 in the CO2 mole fraction. This phase relation agrees with the fact that the composition of grandite from skarn-type ore deposits has a tendency towards andradite.