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Determination of Fe^(3+) and Fe^(2+) Concentrations in Feldspar by Optical Absorption and EPR Spectroscopy

Hofmeister, Anne M. and Rossman, George R. (1984) Determination of Fe^(3+) and Fe^(2+) Concentrations in Feldspar by Optical Absorption and EPR Spectroscopy. Physics and Chemistry of Minerals, 11 (5). pp. 213-224. ISSN 0342-1791. doi:10.1007/BF00308136.

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Ferrous and ferric iron concentrations in feldspars with low total iron content (<0.32 wt% total Fe) were determined from optical and electron paramagnetic resonance (EPR) spectra to better than ±15 percent of the amount present. Optical spectra indicate that Fe^(2+) occupies two distorted M-sites in plagioclases of intermediate structural state. The linear dependence of the Fe^(2+)/Fe total ratio on An content demonstrates that Fe^(2+) substitutes for Ca (not Na) so that the number of Ca-sites is a principal factor in iron partitioning in plagioclase. EPR powder spectra show that the number of sites for Fe^(3+) depends on structural state rather than on plagioclase chemistry. The observed linear correspondence of EPR double-integrated intensities with optical peak areas shows that all Fe^(3+) is tetrahedrally coordinated in both plagioclase and disordered potassium feldspar. Microcline perthites show, in addition to tetrahedral Fe^(3+), a signal due to axially coordinated ferric iron, which we associate with formation of hematite inclusions.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1984 Springer-Verlag. Received August 18, 1983. This work represents part of the doctoral research project of A.M. Hofmeister at the California Institute of Technology, Pasadena, California. We wish to thank Martin Prinz and George Harlow (American Museum of Natural History), David Stewart (U.S.G.S., Reston, Virginia), Eugene F. Foord (U.S.G.S., Denver, Colorado), Subrata Ghose and Anthony Irving (University of Washington, Seattle, Washington), Gordon Brown (Stanford University, Stanford, California), Carl Francis (Harvard University, Cambridge, Massachusetts), Barclay Kamb (Caltech), and Roland Reed (El Cajon, California) for providing samples. We are indebted to Craig Martin, David Blair, and Sunney I. Chan for assistance and advice with EPR spectroscopy; A. A. Chodos for instruction in microprobe and XRF analyses; and Stephanie M. Mattson for help with computer programming. Financial support was provided by NSF grants EAR-7919987, EAR-8212540, and EAR-7904801.
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Official Citation: Determination of Fe3+ and Fe2+ concentrations in feldspar by optical absorption and EPR spectroscopy Anne M. Hofmeister, George R. Rossman Pages 213-224
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:44163
Deposited By: Ruth Sustaita
Deposited On:06 Mar 2014 00:03
Last Modified:10 Nov 2021 16:48

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