Abstract
Destinezite ( \({\text{Fe}}_{{1.97}}^{{3 + }}\) Al0.02)(PO4)0.99(SO4)0.90(OH)1.20⋅5.97H2O (Czech Republic) has been studied by thermal and electron-microprobe analyses, X-ray powder diffraction, and by IR, Raman, and Mössbauer spectroscopy. The enthalpy of formation of destinezite \({\text{Fe}}_{2}^{{3 + }}\) (PO4)(SO4)(OH)⋅6H2O from elements ∆fH0(298.15 K) = –4258 ± 12 kJ/mol was determined by the method of solution calorimetry in lead borate 2PbO⋅B2O3 melt on a Setaram (France) Calvet microcalorimeter. The value of its absolute entropy S0(298.15 K) = 462.0 J/(mol K) was estimated, the entropy of formation ∆fS0(298.15 K) = –2054 J/(mol K), and the Gibbs energy of formation from the elements ∆fG0(298.15 K) = –3646 kJ/mol were calculated.
