Physicochemical and Calorimetric Study of Aluminocopiapite and Thermodynamic Properties of Copiapite-Group Minerals

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The natural basic aqueous aluminum and iron sulfate, aluminocopiapite (Al0.60 Fe_0.07^3 + ) Fe_4.00^3 + [SO4]6.03(OH)1.95 ⋅ 19.54H2O (Blyava, South Urals, Russia), was studied using powder X‑ray diffraction, infrared and Mössbauer spectroscopy, and thermal analysis. The enthalpy of formation from the elements Δ fH_el⁰ (298.15 K) = −11 826 ± 58 kJ/mol was determined by high-temperature melt solution calorimetry on a Tian-Calvet high-temperature heat-flux microcalorimeter “Setaram” (France). Standard entropies and Gibbs energies of formation were estimated for the studied aluminocopiapite and other copiapite-group minerals.