The standard Gibbs free energy of formation of orthorhombic Ca2ZrSi4O1
2 from component oxides ZrO2 (monoclinic), CaO (rock salt), and SiO2 (
quartz) has been determined in the temperature range 973 to 1273 K usi
ng a solid-state cell incorporating single-crystal CaF2 as the electro
lyte: Delta G(f) degrees = -219930 + 11.77T (+/- 1500) J.mol(-1) This
is the only quantitative information now available on the stability of
Ca2ZrSi4O12.