Sodalite: Spectroscopic and Thermochemical Investigations

Two sodalite samples (sample I is Na₈Al₆Si₆O₂₄Cl₂⋅0.4H₂O from the Kovdor alkaline ultramafic massif with carbonatites in the Murmansk region, Russia, and sample II is Na₈Al₆Si₆O₂₄Cl₂⋅0.2H₂O from the Bayan Kol nepheline syenite and miaskite massif in the Republic of Tyva) were studied by thermal and electron-microprobe analyses, powder X-ray diffraction, photoluminescence, and by IR, Raman, and ESR spectroscopy. Solution melt calorimetry was applied to determine the enthalpy of formation from elements for water-bearing sodalite samples: −13536 ± 10 (I) and −13503 ± 19 (II) kJ/mol. The enthalpy of formation of sodalite of the theoretical composition Na₈Al₆Si₆O₂₄Cl₂ was evaluated at Δ_fH⁰(298.15 K) = −13446 ± 11 kJ/mol. The data obtained on the enthalpy of formation of sodalite and literature data on its S⁰(298.15 K) were used to calculate the standard Gibbs energies of formation of anhydrous and of water-bearing sodalite.