Application of new thermodynamic data to grossular phase relations

Abstract

Recent low temperature, adiabatic calorimetric heat capacity measurements for grossular have been combined with DSC measurements to give entropies up to 1000 K. In conjunction with enthalpy of solution values for grossular, these data have yielded Δ H f o (298.15K) and Δ G f o (298.15K) values of −1583.2 ± 3.5 and −1496.74 ± 3.7 kcal mol −1 respectively. For 15 reactions in the CaO-Al 2 O 3 -SiO 2 -H 2 O system, thermodynamically calculated P-T curves have been compared with experimental reversals and have shown good agreement in most cases. Calculations indicate that gehlenite is probably totally disordered. Estimates of zoisite and lawsonite entropies are consistent with the phase equilibrium and grossular data, but estimates of the entropies of pyrope and andradite show large discrepancies when compared with experimental reversals.