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Kinetics of Fe2+-Mg distribution in aluminous orthopyroxenes

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Abstract

Kinetic studies of isothermal heating experiments (600–800° C) on aluminous pyroxenes (Mg0.942Fe 2+0.880 Fe 3+0.068 Mn0.016Ca0.010Al0.084) (Si1.848Al0.152) permit the determination of rate constant of isothermal disordering as 2.5457 E13(±1.4 E13) min−1. The activation energy is determined as 278 (±23) kJ/mol. Data on two other aluminous pyroxenes at 700° C indicate that the rate constant decreases significantly with increasing amount of trivalent cations. There is a similar but reverse correlation between the concentration of trivalent cations and the Fe2+-Mg equilibrium distribution between sites. The site distribution coefficient increases with increasing concentration of trivalent cations at constant temperature.

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Authors and Affiliations

  1. Department of Geology, Brooklyn College, 11210, Brooklyn, NY, USA

    S. K. Saxena

  2. C.N.R. Centro di Studio per la Cristallografia Strutturale c/o Dipartimento di Scienze della Terra, Università di Pavia, Via Bassi, 4, I-27100, Pavia, Italy

    V. Tazzoli & M. C. Domeneghetti

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  1. S. K. Saxena
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  2. V. Tazzoli
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  3. M. C. Domeneghetti
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Saxena, S.K., Tazzoli, V. & Domeneghetti, M.C. Kinetics of Fe2+-Mg distribution in aluminous orthopyroxenes. Phys Chem Minerals 15, 140–147 (1987). https://doi.org/10.1007/BF00308776

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  • DOI: https://doi.org/10.1007/BF00308776

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