A thermochemical, X-ray, IR- and Raman spectroscopy study of the natural minerals of the apophyllite group: fluorophosphite - (K) KCa4 [Si8O20] F. 8H2O (Maharashtra, India) (I) and hydroxylapophyllite- (K) KCa4 [Si8O20] OH. 8H2O (Norilsk, Russia) (II). The first data on enthalpies of formation from the elements of the minerals studied are obtained on the high-temperature heat conducting microcalorimeter Tiana-Calvet \"Setaram\" (France) by the method of melt calorimetry of dissolution (-13205 ± 13 kJ / mol (I) and -13054 ± 20 kJ / mol (II)). The values of their standard entropies and Gibbs energies of formation were estimated.
Key words: fluorapophyllite (K), hydroxylapophyllite (K), enthalpy of formation, Calvet microcalorimetry