The purpose of this investigation was to obtain accurate and precise thermodynamic quantities for well-characterized specimens of analcime and dehydrated analcime, and to relate the results to processes of geochemical interest. Calorimetrie measurements have been carried out on a pure specimen of analcime whose composition was Na0.96 Al0.96Si2.04O6·H2O and on the corresponding anhydride. The low-temperature heat capacity, standard enthalpy of formation (298.15 K), and high-temperature enthalpy increments have been determined by adiabatic, solution, and drop-calorimetric techniques, respectively. Thermodynamic functions have been calculated for analcime (to 600 K) and for dehydrated analcime (to 1000 K). The following values at T = 298.15 K and at a pressure of 1 bar have been obtained:

ΔHf∘(T)kJ/molCp∘(T)J/(mol⋅K)S°(T) J/(mol·K)ΔGf∘(T)kJ/mol
analcime dehydrated −3296.9±3.3 211.53±0.21 226.75±0.23 −3077.2±3.3 
analcime −2970.2±3.5 163.59±0.16 171.71±0.17 −2803.7±3.5 
ΔHf∘(T)kJ/molCp∘(T)J/(mol⋅K)S°(T) J/(mol·K)ΔGf∘(T)kJ/mol
analcime dehydrated −3296.9±3.3 211.53±0.21 226.75±0.23 −3077.2±3.3 
analcime −2970.2±3.5 163.59±0.16 171.71±0.17 −2803.7±3.5 
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An examination of the thermodynamics of the following reactions has been carried out in the light of the results obtained in the present study:
analcime = dehydrated analcime + H2O(g)low albite + H2O(I) = analcime + SiO2(aq)
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