A study of dachiardite,a natural zeolite of the mordenite group

Dachiardite of the composition (Na_2.21K_0.35Ca_0.66Mg_0.10)Al_4.41Si_19.67O₄₈] · 11.8H₂O (Tedzami, Georgia), a natural zeolite of the mordenite group, was studied using a Tian-Calvet high-temperature microcalorimeter. Melt solution calorimetry was used to determine the enthalpy of formation of the mineral from oxides (?613±45 kJ/mol) and elements (?26595±50kJ/mol). The obtained experimental and literature data were used to calculate the Gibbs energy of formation of dachiardite from elements. The thermodynamic properties of the hypothetical limiting members of the isomorphous series (Na, K, Ca)Al₄Si₂₀O₄₈] · 13H₂O were estimated.