Mirko Schoenitz, Alexandra Navrotsky; Enthalpy of formation of katoite Ca 2 Al 2 [(OH) 4 ] 3 ; energetics of the hydrogarnet substitution. American Mineralogist ; 84 (3): 389–391. doi: https://doi.org/10.2138/am-1999-0323
The silicon-free end member of the hydrogrossular solid solution series, katoite Ca 3 Al 2 [(OH) 4 ] 3 , was synthesized in a solid-media, piston-cylinder apparatus. The enthalpy of formation from the component oxides was measured by high-temperature oxide melt calorimetry and found to be Delta H f = -255.6+ or -12.2 kJ/mol; the resulting enthalpy of formation from the elements is Delta H f = -5551.5+ or -16.4 kJ/mol. From this value, enthalpies for breakdown reactions of hydrogrossular were calculated and the relative energetic stability of katoite evaluated.