A thermodynamic model for subsolidus equilibria in the system CaO-MgO-Al2O3-SiO2

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doi: 10.1016/0016-7037(84)90358-2
Authors:Wood, Bernard J.; Holloway, John R.
Author Affiliations:Primary:
Northwest. Univ., Dep. Geol. Sci., Evanston, IL, United States
Ariz. State Univ., Dep. Chem., United States
Volume Title:Geochimica et Cosmochimica Acta
Source:Geochimica et Cosmochimica Acta, 48(1), p.159-176. Publisher: Pergamon, Oxford, International. ISSN: 0016-7037
Publication Date:1984
Note:In English. 66 refs.; illus. incl. 3 tables
Summary:The study integrates phase equilibrium and calorimetric data for the following phases in the CaO-MgO-Al2O3-SiO2 system: clinopyroxene, orthopyroxene, garnet, forsterite, anorthite, spinel, kyanite, sillimanite, corundum and quartz. The internally consistent data set includes mixing properties for clinopyroxene, orthopyroxene, and garnet solid solutions and enables calculation of any equilibrium involving the components of the above 10 phases under any desired P, T conditions. Major conclusions of the study are: (1) Spinel appears to have an enthalpy of Mg-Al exchange on the order of 20 Kcal or more, substantially above the calorimetrically measured value. (2) CaAl2SiO6 pyroxene has virtually complete Al-Si disorder. (3) Enstatite has an enthalpy of formation from oxides at 1000 K of about-16840 cal/mole, substantially greater than the calorimetric value of -17620±340 cal. (4) Anorthite has about 0.6 cal/K entropy of Al-Si disorder. (5) CMAS garnets of between Pyrope100 and Pyrope80Grossular20 composition have almost zero excess entropy. (6) Nonstoichiometry in clinopyroxene has a moderate but predictable influence on reaction boundaries in SiO2-saturated compositions. [T.R.]
Subjects:Anorthite; Chain silicates; Coexisting minerals; Corundum; Enthalpy; Entropy; Feldspar group; Forsterite; Framework silicates; Geochemistry; Kyanite; Models; Nesosilicates; Olivine group; Orthosilicates; Oxides; P-T conditions; Phase equilibria; Plagioclase; Pyroxene group; Quartz; Silica minerals; Silicates; Sillimanite; Solid solution; Spinel; Stability; Stoichiometry; Theoretical studies; Thermodynamic properties; CaO-MgO-Al<2`O<3`-SiO<2`; Garnet
Abstract Numbers:84M/4016
Record ID:1984052114
Copyright Information:GeoRef, Copyright 2019 American Geosciences Institute.
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