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Mixed Valence of Iron in Minerals with Cation Clusters

Amthauer, Georg and Rossman, George R. (1984) Mixed Valence of Iron in Minerals with Cation Clusters. Physics and Chemistry of Minerals, 11 (1). pp. 37-51. ISSN 0342-1791. doi:10.1007/BF00309374.

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The valence and distribution of iron in vivianite, lazulite, babingtonite, rockbridgeite, acmite, aegirine-augite, hedenbergite, and ilvaite were studied with optical and Mössbauer spectroscopy. Optically activated intervalence charge transfer between Fe^2+ and Fe^3+ in neighboring sites through common edges or faces is observed in all these minerals irrespective of the polymerization of the iron-oxygen polyhedra ranging from finite clusters to infinite structural units. However, a distinct decrease occurs in the energy of the corresponding optical absorption band with increasing number of Fe^2+ and Fe^3+ ions involved in the charge transfer process. Thermally activated electron delocalization between Fe^2+ and Fe^3+ occurs only if Fe^2+ and Fe^3+ occupy crystallographically equivalent or geometrically very similar neighboring sites which share common edges to form extended structural units such as the ribbon in ilvaite. If the Fe-O polyhedra form finite clusters of two, three, or four polyhedra (e.g., in vivianite, lazulite, and babingtonite, respectively) no thermally-activated mixed-valence states of iron are observed. In aegirine, extended regions of the M1 chain are statistically occupied by Fe^2+ and Fe^3+ giving rise to thermally-activated electron delocalization in addition to the intervalence band in the optical absorption spectrum. The intensity of the optical intervalence absorption has been measured in a number of systems: ɛ values range from 60 to 210.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1984 Springer-Verlag. Received February 9, 1983. Samples of minerals were provided by R.H. Currier, Arcadia, California, P.B. Moore, University of Chicago, the Smithsonian Institution, and the Los Angeles County Museum of Natural History. Pyroxene chemical analyses were obtained in part from unpublished data by D.S. Goldman. R.G. Burns and F. Hawthorne provided helpful reviews of the work. This work was funded in part by the National Science Foundation under grants EAR-7904801 and EAR-8212540.
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Official Citation:Amthauer, G., & Rossman, G. (1984). Mixed valence of iron in minerals with cation clusters. Physics and Chemistry of Minerals, 11(1), 37-51. doi: 10.1007/bf00309374
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44005
Deposited By: Jason Perez
Deposited On:26 Feb 2014 17:44
Last Modified:10 Nov 2021 16:46

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