Ti ³⁺ – and Ti ⁴⁺ – rich fassaites at the birth of the solar system: Thermodynamics and applications

A thermodynamic model is developed for pyroxenes in the chemical (mineralogical) system CaMgSi~2~O~6~ (diopside, Di, 1) -- CaTiAlSiO~6~ (grossmanite, Gr, 2) --CaMg~1/2~ Ti~1/2~AlSiO~6~ (alumino -- buffonite, AlBf, 3) -- CaAl~2~SiO~6~ (Calcium Aluminum Tschermaks, CATS, 4), *aka* fassaites. It is formulated for the assumptions of molecular mixing between AlBf and Di, Gr and CATS components, and that the reduction in configurational entropy...