Experimental techniques for calorimetry at 700-800°C using a Calvet-type microcalorimeter are described. This method is applied to solution calorimetry in molten oxide solvents to measure the enthalpies of formation of silicates and related minerals, the enthalpies of phase transitions, and the enthalpies of mixing in solid solutions. The accurate measurements are made using the small amounts of sample (about 200 mg total). The enthalpies of high-pressure phase transition of silicates are used to calculate the equilibrium phase relations at high pressures and high temperatures.
