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Crystal field stabilization energies of almandine-pyrope and almandine-spessartine garnets determined by FTIR near infrared measurements

Geiger, Charles A. and Rossman, George R. (1994) Crystal field stabilization energies of almandine-pyrope and almandine-spessartine garnets determined by FTIR near infrared measurements. Physics and Chemistry of Minerals, 21 (8). pp. 516-525. ISSN 0342-1791.

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The band positions of three partially overlapping Fe^(2+) spin-allowed transitions located between 4000 and 9000 cm^(−1) in almandine-pyrope and almandinespessartine garnets solid solutions were measured using near-infrared (NIR) spectroscopy. The crystal field stabilization energies (CFSE) along both binaries were calculated assuming a splitting of 1100 cm^(−1) for the lower orbitals. The CFSE show a slight increase along the almandine-spessartine binary from 3730 to 3810 cm^(−1) and a larger increase from 3730 to 3970 cm^(−1) for the almandine-pyrope binary. Dodecahedral Fe^(2+)-site distortion increases with an increase in spessartine component and decreases with increasing pyrope component, in agreement with average dodecahedral site distortions determined from diffraction experiments. The excess CFSE's along both joins are negative. For the almandinespessartine binary they are small, but are about 3.5 times larger in magnitude along the join almandine-pyrope, where an interaction parameter of W= -2.9 KJ/mole has been derived from a symmetric mixing model. The excess CFSE are relatively small compared to the magnitudes of the excess enthalpies of mixing that have been assigned to garnet solid solutions. Moreover, they give no indication which could support the positive and asymmetric excess enthalpies of mixing that have been proposed for almandine-pyrope solid solutions.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1994 Springer-Verlag. Received January 12, 19941 Revised, accepted October 6, 1994. C.A.G. would like to thank Drs. Ch. Chopin and D. Smith for kindly providing some of the garnets used in this study. Dr. B. Winkler read an early draft and offered helpful changes and Prof. Klaus Langer gave a number of critical suggestions on improving the final manuscript. Financial support was supplied through grants EAR 89 16064 and EAR 92 18980 from the National Science Foundation (USA) and Ge 659-2/1 from the "Deutsche Forschungsgemeinschaft" as part of a priority program concerning element partitioning.
Funding AgencyGrant Number
NSFEAR 89 16064
NSFEAR 92 18980
Deutsche Forschungsgemeinschaft (DFG)Ge 659-2/1
Issue or Number:8
Record Number:CaltechAUTHORS:20130731-133407774
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ID Code:39679
Deposited By: Jason Perez
Deposited On:01 Aug 2013 14:35
Last Modified:03 Oct 2019 05:09

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