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Dielectric constants of silicate garnets and the oxide additivity rule

Shannon, Robert D. and Rossman, George R. (1992) Dielectric constants of silicate garnets and the oxide additivity rule. American Mineralogist, 77 (1-2). pp. 94-100. ISSN 0003-004X.

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The dielectric constants and dielectric loss values of a series of garnets were measured at l MHz using a two-terminal method and empirically determined edge corrections. The results are five intermediate pyrope-almandine samples, k'=11.96-12.35; spessartine, k'=11.65; two andradite samples, k'=10.53-10.59; and three grossular samples, k'=8.53-8.8l. The deviations of measured dielectric polarizabilities as determined using the Clausius-Mosotti equation from those calculated using the sum of oxide polarizabilities according to ɑ_D(M_2M'X_4) = 2ɑ_D(MX) + ɑ_D(M'X_2) is +5.0 to 6.5% for the pyrope-almandine samples,+ 1.9% for spessartine, -2.3% of or the andradite samples, and -5.5 to -7.0% for grossular. These deviations from additivity are believed to result from garnet structural constraints leading to "rattling" Mg ions and "compressed" Ca ions.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1992 Mineralogical Society of America. Manuscript received January 28, 1991. Manuscript accepted September 16, 1991. We thank R.W. Shiffer for sample preparation, M.A. Subramanian and R.A. Oswald for making the capacitance measurements, A. Brown (Studsvik Eneryiteknik AB, Nykoping, Sweden) and C. Foris for obtaining cell dimensions, P.K. Carpenter (California Institute of Technology, Pasadena, Califonia) for microprobe data, and W.B. White for providing data on the Madagascar almandine and Chihuahua grossular prior to publication. We are indebted to R.M. Hazen for providing the pyrope Madagascar (USNM no.132950). The pyrope from northeastern Arizona was obtained by R.T. Cygan with permission from the Navajo Nation Minerals Department. We gratefully acknowledge M. O'Keeffe and F.C. Hawthorne for reviewing the manuscript prior to publication. This work was supported in part by NSF grant EAR-8618200. E.I. Du Pont de Nemours contribution no. 5769.
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Caltech Division of Geological and Planetary Sciences 5769
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Official Citation:Dielectric constants of silicate garnets and the oxide additivity rule 94-100
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44126
Deposited By: Ruth Sustaita
Deposited On:04 Mar 2014 22:00
Last Modified:03 Oct 2019 06:14

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