Abstract
This paper presents the point-defect thermodynamics for fayalite and olivine solid solutions (Fe x Mg1−x )2SiO4. By means of thermogravimetry, the metal-to-oxygen ratio of these silicates has been determined as a function of oxygen potential, compositionx and temperature. Experiments were performed in the range of 1,000° C≦T≦1,280° C and 0.2≦x≦1.0. It is found that V ″Me , Fe ·Me and the associate {Fe′ ′Si Fe ·Me } are the majority defects. With this knowledge it is possible to calculate the nonstoichiometry at given temperature as a function of\(p_{O_2 } \) and\(a_{SiO_2 } \). The cation vacancy concentration shows a\(p_{O_2 }^{1/5} \)-dependence (forx≧0.2) and increases at givenT and\(p_{O_2 } \) almost exponentially with compositionx. In the composition range studied here, the silicates show an oxygen excess, and FeO is more soluble in the olivine than SiO2.
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Nakamura, A., Schmalzried, H. On the nonstoichiometry and point defects of olivine. Phys Chem Minerals 10, 27–37 (1983). https://doi.org/10.1007/BF01204323
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DOI: https://doi.org/10.1007/BF01204323