Thermodynamic Properties of Fluorapophyllite-(K) and Hydroxyapophyllite-(K)

Abstract

A thermochemical study of natural apophyllite-group minerals, fluorapophyllite-(K) KCa₄[Si₈O₂₀]F ⋅ 8H₂O (Maharashtra, India) (I) and hydroxyapophyllite-(K) KCa₄[Si₈O₂₀]OH ⋅ 8H₂O (Norilsk, Russia) (II), was carried out on a high-temperature heat-flux Tian-Calvet Setaram (France) microcalorimeter using the melt solution calorimetry method. The first data on the enthalpies of formation from elements are obtained for the minerals studied: –13205 ± 13 kJ/mol (I) and –13054 ± 20 kJ/mol (II). The values of their standard entropies and Gibbs energies of formation are estimated.