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The hydrous component in garnets: pyralspites

Aines, Roger D. and Rossman, George R. (1984) The hydrous component in garnets: pyralspites. American Mineralogist, 69 (11-12). pp. 1116-1126. ISSN 0003-004X.

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Natural pyralspite garnets have been found to commonly contain a hydrous component, ranging in concentration from 0.02 to 0.25 wt.% as H_2O. Anhydrous pyralspites of crustal origin are rare. Of forty crustal garnets examined, only two were anhydrous. The mosthydrous garnets were spessartines from igneous pegmatites. Metamorphic garnets had lower water contents, and frequently also contained hydrous inclusions. The infrared absorptions of the hydrous component in the garnet end members are characteristic and consist of 2 to 4 narrow bands centered at 3640 cm^(-1) in spessartine, 3500 cm^(-1) in almandine, and 3670 cm^(-1) in pyrope. The IR spectra indicate that the hydrous component Is not m the form of molecular H_2O; the most likely form is H_4O^(4-)_4 substituting for SiO^(4-)_4 but other substitutions involving multiple OH^- groups on one site are consistent with the data. The concentration of OH (as H_2O) in garnets may be determined from the integral absorptivity (K) in the 3700-3400 cm^(-1) region, although K varies with chemistry from 3700-6000 (l mol^(-1)_2O cm^(-2)) in end members to 120-600 in intermediate compositions.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1984 Mineralogical Society of America. Manuscript received, October 14, 1983; accepted for publication, June 20, 1984. We would like to thank Douglas Smith (U. Texas), Edward S. Grew (UCLA), Georg Amthauer (Marburg), Stein B. Jacobsen (Caltech), R. Larry Edwards (Caltech), L. T. Silver (Caltech), John S. White (Washington, DC) and Mary L. Johnson (Harvard) for generously providing samples used in this study, and Anne M. Hofmeister (Caltech) and Robert E. Criss (USGS) for conducting the hydrogen manometry. This study was in part funded by the National Science Foundation (Grant EAR-7919987).
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Caltech Division of Geological and Planetary Sciences3974
Issue or Number:11-12
Record Number:CaltechAUTHORS:20130514-103358686
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Official Citation: Roger D. Aines and George R. Rossman The hydrous component in garnets; pyralspites American Mineralogist, December 1984, v. 69, p. 1116-1126
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38491
Deposited By: Ruth Sustaita
Deposited On:14 May 2013 17:52
Last Modified:26 Nov 2019 11:15

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