The stability of Fe-Mg chlorites in hydrothermal solutions; II, Thermodynamic properties

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doi: 10.1346/000986002320679323
Authors:Aja, Stephen U.
Author Affiliations:Primary:
University of New York, Department of Geology, Brooklyn, NY, United States
Volume Title:Clays and Clay Minerals
Source:Clays and Clay Minerals, 50(5), p.591-600. Publisher: Clay Minerals Society, Clarkson, NY, United States. ISSN: 0009-8604
Publication Date:2002
Note:In English. 28 refs.; illus., incl. 2 tables
Summary:The hydrothermal stabilities of a low-Fe clinochlore and a high-Mg chamosite, in the presence of kaolinite, were investigated recently at T T≤200°C and Pv = PH2O (Aja and Small, 1999; Aja and Dyar, 2002). Standard state thermodynamic properties (S0298, ΔfH01,298 and ΔfG01,298) have been obtained for the two chlorites whose structural formulae are (Al2.33 Fe2+1.00 Fe3+0.14 Ca0.02 Mn0.01 Ni0.02 Cr0.01 Mg8.40[]0.07) (Si5.66 Al2.34)O20 (OH)16 and (Fe3+0.60 Fe2+5.43 Mg2.30 Al2.98 Mn0.05 Ca0.03 Zn0.01[]0.60) (Si5.63 Al2.37)O20 (OH)16. For the low-Fe clinochlore, the respective thermochemical properties are 430 J mol-1 K-1, -8770.64±35.24 kJ mol-1, and -8120.54±32.63 kJ mol-1. ΔfH01,298, ΔfG01,298, and S0298, similarly obtained for the Windsor chamosite are -7851.29±23.14 kJ mol-1, -7271.01±21.43 kJ mol-1 and 668±5 J mol-1 K-1, respectively. Ideal site-mixing models of chlorite composition, along the chamosite-clinochlore binary, fail to model satisfactorily these chlorite-fluid equilibria only at lower temperatures (T<175°C). The magnitudes of the excess thermodynamic properties calculated for these chlorites, within the ternary clinochlore-daphnite-sudoite system, suggest significant deviations from ideality.
Sections:Experimental mineralogy
Subsections:Silicates
Subjects:Alkaline earth metals; Chamosite; Chemical properties; Chemical reactions; Chlorite; Chlorite group; Clay mineralogy; Clay minerals; Clinochlore; Experimental studies; Geochemistry; Hydrothermal alteration; Iron; Kaolinite; Magnesium; Metals; Metasomatism; Sheet silicates; Silicates; Solutions; Stability; Sudoite; Thermodynamic properties
Abstract Numbers:03M/342
Record ID:2003005684
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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