Thermodynamic Properties of Pectolite

Abstract

Pectolite H1.00Na0.96Ca2.00Mn2+0.02Si3.00O9 from nepheline−feldspathic veins in the Kovdor massif, Kola Peninsula, Russia, was studied by X-ray diffraction (XRD), IR and Raman spectrometry, microprobe analysis (EPMA), and thermal analysis. The enthalpy of formation of pectolite HNaCa2Si3O9.from elements ∆fH° (298.15 K) = –4651.0 ± 4.3 kJ/mol was determined by melt solution calorimetry on a Setaram Tian–Calvet (France) microcalorimeter. The enthalpy of formation of serandite HNaMn2Si3O9, the manganese end member of the pectolite–serandite isomorphic series, was determined to be ΔH(298.15 K) = −4052.6 ± 4.4 kJ/mol. The absolute entropies and Gibbs energies of pectolite and serandite were calculated.