An experimental and thermodynamic study of cymrite and celsian stability in the system BaO-Al2O3-SiO2-H2O

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doi: 10.1127/ejm/4/2/0251
Authors:Graham, Colin M.; Tareen, Jalees A. K.; McMillan, Paul F.; Lowe, Barrie M.
Author Affiliations:Primary:
University of Edinburgh, Department of Geology and Geophysics, Edinburgh, United Kingdom
University of Mysore, India
Arizona State University, United States
Volume Title:European Journal of Mineralogy
Source:European Journal of Mineralogy, 4(2), p.251-269. Publisher: Schweizerbart'sche Verlagsbuchhandlung (Nägele u. Obermiller), Stuttgart, Federal Republic of Germany. ISSN: 0935-1221
Publication Date:1992
Note:In English. 40 refs.; 5 tables
Summary:The stabilities and growth kinetics of celsian and cymrite have been investigated in the system BaO-Al2O3-SiO2- H2O at <= 10 kbar and <= 800 degrees C; a broad area of P-T space has been identified at low P and T in which cymrite grows rapidly and metastably in runs of short duration, being replaced by celsian in longer runs. The equilibrium cymrite reversible double half arrows celsian + H2O has been tightly bracketed at approx 9.7 kbar, 800 degrees ; 9.0 kbar, 710 degrees C; 8.0 kbar, 580 degrees C; results at lower P and T confirm that cymrite is only stable at high P, providing a valuable metamorphic geothermometer. Cymrite is not stable in low P-T sedimentary and hydrothermal environments and documented natural occurrences in these environments must be considered to have resulted from metastable growth and persistence in the celsian stability field. The molecular H2O contents of cymrites vary systematically with PH2O and T of synthesis, increasing with increasing P and decreasing T to a maximum of 1 H2O per formula unit. The incorporation of H2O yields an enthalpy change of approx 59 kJ/mol and an entropy change of approx 133 J/K/mol; isopleths have been calculated for the equilibrium water content of cymrite as a function of PH2O and T. [R.A.H.]
Subjects:Alkali feldspar; Barium feldspar; Celsian; Cymrite; Feldspar group; Framework silicates; Phase equilibria; Sheet silicates; Silicates; Thermodynamic properties; Water; BaO-Al<2`O<3`-SiO<2`-H<2`O
Abstract Numbers:92M/4117
Record ID:1995056225
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute. Reference includes data from Mineralogical Abstracts, United Kingdom, Twickenham, United Kingdom
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