Heat capacity measurements of CaAlSiO₄F from 5 to 850 K and its standard entropy

Heat capacity (C_P) data of Al-F-bearing titanite are presented that yield the standard entropy S_298.15° of F-Al-titanite CaAlFSiO₄ (FAT). C_P of synthetic FAT was measured with relaxation calorimetry and differential scanning calorimetry between 5 and 764 K. The results constrain S_298.15° to be 115.4 ± 2.0 J/(mol·K) and subsequently the standard Gibbs free energy of formation from the elements, Δ_fG°, of CaAlSiO₄F to be between -2583 ± 3.0 and -2588 ± 3.0 kJ/mol, and the standard enthalpy of formation from the elements, Δ_fH°, to lie between -2728 ± 3.0 and -2733 ± 3.0 kJ/mol depending on the thermodynamic data retrieval approach. These data, in turn, can be used to quantitatively model high-grade and UHP fluid-rock interaction. The calculation of future petrogenetic grids involving F-bearing minerals and titanite solid solutions in the system CaTiSiO₄O-CaAlSiO₄F will only be possible by expanding existing internally consistent thermodynamic databases to the F-system.