Thermodynamic study of calcic amphiboles

• Published in: Geochemistry international 2017-09, Vol.55 (9), p.814-821
• Main Authors: Ogorodova, L. P., Kiseleva, I. A., Vigasina, M. F., Mel’chakova, L. V., Bryzgalov, I. A., Ksenofontov, D. A.
• Format: Article
• Language: English
• Subjects: Amphiboles; Calorimetry; Chemicals; Composition; Earth and Environmental Science; Earth Sciences; Enthalpy; Entropy; Free energy; Free energy of formation; Geochemistry; Gibbs free energy; Heat measurement; Heat of formation; High temperature; Iron; Temperature; Thermodynamics; Tremolite
• ISSN: 0016-7029; 1556-1968
• DOI: 10.1134/S0016702917080067

The paper reports original thermochemical data on six natural amphibole samples of different composition. The data were obtained by high-temperature melt solution calorimetry in a Tian–Calvet microcalorometer and include the enthalpies of formation from elements for actinolite Ca 1.95 (Mg 4.4 Fe 0.5 2+ Al 01 )[Si 8.0 O 22 ](OH) 2 (–12024 ± 13 kJ/mol) and Ca 2.0 (Mg 2.9 Fe 1.9 2+ Fe 0.2 3+ )[Si 7.8 Al 0.2 O 22 ](OH) 2 , (–11462 ± 18 kJ/mol), and Na 0.1 Ca 2.0 (Mg 3.2 Fe 1.6 2+ Fe 0.2 3+ )[Si 7.7 Al 0.3 O 22 ](OH) 2 (–11588 ± 14 kJ/mol); for pargasite Na 0.5 K 0.5 Ca 2.0 -(Mg 3.4 Fe 1.8 2+ Al 0.8 )[Si 6.2 Al 1.8 O 22 ](OH) 2 (–12316 ± 10 kJ/mol) and Na 0.8 K 0.2 Ca 2.0 (Mg 2.8 Fe 1.3 3+ Al 0.9 ) [Si 6.1 Al 1.9 O 22 ](OH) 2 (–12 223 ± 9 kJ/mol); and for hastingsite Na 0.3 K 0.2 Ca 2.0 (Mg 0.4 Fe 1.3 2+ Fe 0.9 3+ Al 0.2 ) [Si 6.4 Al 1.6 O 22 ](OH) 2 (‒10909 ± 11 kJ/mol). The standard entropy, enthalpy, and Gibbs free energy of formation are estimated for amphiboles of theoretical composition: end members and intermediate members of the isomorphic series tremolite–ferroactinolite, edenite–ferroedenite, pargasite–ferropargasite, and hastingsite.