Activity Measurements in Orthosilicate and Metasilicate Solid Solutions. II. MgSiO3-FeSiO3 at 1154, 1204, and 1250°C

Abstract

Abstract The activity-composition relation in the pyroxene solid solution, MgSiO3–FeSiO3, is determined by the quenching method in the atmosphere of a gas mixture of CO2 and H2 at 1154, 1204, and 1250°C. A non-ideality is found in the solution at these temperatures, and it increases with a decrease in the temperature. The standard free energy values of the formation of ferrosilite, FeSiO3, from metallic iron, silica, and oxygen are −42.5±0.3, −41.7±0.2, and −41.3±0.2 kcal per mole of FeSiO3 at 1154, 1204, and 1250°C respectively. Using the data by Darken and Gurry, the standard free energies of the formation of ferrosilite from wüstite and silica are obtained as −1.8±0.3, −1.5±0.2, and −1.8±0.2 kcal per mole of FeSiO3 at 1154, 1204, 1250°C respectively.