Transposed-temperature-drop calorimetry performed in a Setaram HT 1500 calorimeter was used to study directly the melting of mixtures of crystalline diopside (CaMgSi2O6, anorthite (CaAl2Si2O8), and pseudowollastonite (Wo, CaSiO3) at 1773 K. Thermochemical cycles used completely avoid the glassy state by transforming crystals directly to melts. The results, zero or slightly negative enthalpies of mixing in Di-An-Wo melts at 1773 K, indicate that very small heat effects accompany any changes in melt structure upon mixing. Athermal mixing is prevalent in the diopside-rich region and along the Di-An join, whereas mixing is slightly exothermic in the rest of the Di-An-Wo system, especially in the Wo-rich region. Our data are consistent with an enthalpy of fusion of pseudowollastonite of 57 ± 5 kJ/mol at the melting point, 1827 K.
ASJC Scopus subject areas
- Geochemistry and Petrology