Using the method advanced by Y. Tardy et al. and expanded recently by Gao Ping for the prediction of Gibbs free energies of formation of silicates, the author has caleulated Gibbs free cnergics of formation of talaski...Using the method advanced by Y. Tardy et al. and expanded recently by Gao Ping for the prediction of Gibbs free energies of formation of silicates, the author has caleulated Gibbs free cnergics of formation of talaskite(Fe0.80^3+Fe1.60^2+Ca0.01Mg0.13)Si0.89O4,ferrifayalite(Fe0.80^3+Fe0.71^2+Ca0.02Mg0.01Mn0.22)Si0.50O4,laihunite(Fe1.00^3+Fe0.58^3+)Si0.96O4 and its ideal foumula(Fe1.00^3+ Fe0.50^2+)SiO4,which are-326.55,-319.95,-311.14 and -314.01 keal/mole,respectively,with the errors to be about ±3keal/mole.In addition,the influence of temperature and pressure has been estimated on the free energy of reaction(△Gr^0)of laihunite from component oxides. The calculations indicate that the free energy of reaction (△Gr^0) of this group of minerals from component oxides shows a tendency to vary from negative to positive with increasing Fe^3+ and decreasing Fe&2+ content. At the high temperature, △Gr^0 displays no tendency to become more negative, even under pressure-rising conditions.Therefore, it is difficult for component oxides to generate minerals similar to laihunite in composition. The author suggests that laihunite may be an intermediate mcta-stablc phase appearing in the process of oxidation-decomposition of Fe^++-rich silicates, such as fayalite, pyroxenc, ete. due to the inerease of oxygen fugaeity during the alteration.展开更多
文摘Using the method advanced by Y. Tardy et al. and expanded recently by Gao Ping for the prediction of Gibbs free energies of formation of silicates, the author has caleulated Gibbs free cnergics of formation of talaskite(Fe0.80^3+Fe1.60^2+Ca0.01Mg0.13)Si0.89O4,ferrifayalite(Fe0.80^3+Fe0.71^2+Ca0.02Mg0.01Mn0.22)Si0.50O4,laihunite(Fe1.00^3+Fe0.58^3+)Si0.96O4 and its ideal foumula(Fe1.00^3+ Fe0.50^2+)SiO4,which are-326.55,-319.95,-311.14 and -314.01 keal/mole,respectively,with the errors to be about ±3keal/mole.In addition,the influence of temperature and pressure has been estimated on the free energy of reaction(△Gr^0)of laihunite from component oxides. The calculations indicate that the free energy of reaction (△Gr^0) of this group of minerals from component oxides shows a tendency to vary from negative to positive with increasing Fe^3+ and decreasing Fe&2+ content. At the high temperature, △Gr^0 displays no tendency to become more negative, even under pressure-rising conditions.Therefore, it is difficult for component oxides to generate minerals similar to laihunite in composition. The author suggests that laihunite may be an intermediate mcta-stablc phase appearing in the process of oxidation-decomposition of Fe^++-rich silicates, such as fayalite, pyroxenc, ete. due to the inerease of oxygen fugaeity during the alteration.
基金supported by the National Natural Science Foundation of China(No.U20A20273)the Natural Science Foundation for Distinguished Young Scholars of Hunan Province,China(No.2022JJ10078)the Innovation Driven Project of Central South University,China(No.2020CX028).
