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A model for the irradiative coloration of smoky feldspar and the inhibiting influence of water

Hofmeister, Anne M. and Rossman, George R. (1985) A model for the irradiative coloration of smoky feldspar and the inhibiting influence of water. Physics and Chemistry of Minerals, 12 (6). pp. 324-332. ISSN 0342-1791 . http://resolver.caltech.edu/CaltechAUTHORS:20130724-082249412

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Abstract

Radiation-induced smoky color and associated electron paramagnetic resonance (EPR) signals develop only in potassium feldspar (KalSi_3O_8) free of structurally bound molecular water. Fluid inclusion water does not influence coloration. The integrated intensity of each of the four bands (11,600, 16,200, 19,100, and 27,200 cm^(−1)) in the optical absorption spectra are linearly correlated with the doubly-integrated intensity of a broad, asymmetric first derivative at g_(eff)=2.027 in EPR spectra. In microcline, the EPR pattern is resolved into an asymmetric six-line pattern at g_(eff)=2.024 and a single derivative at g_(eff)=2.009 which, based on analogy to alkali-silicate glass, are due respectively to [SiO_4/K^+]^(2+) and a hole shared between two nonbonding oxygens on Si. We propose that structural water inhibits formation of smoky centers in feldspar by releasing atomic hydrogen during irradiation which destroys centers while diffusing towards a stable site.


Item Type:Article
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URLURL TypeDescription
http://dx.doi.org/10.1007/BF00654342 DOIArticle
http://link.springer.com/article/10.1007%2FBF00654342PublisherArticle
Additional Information:© 1985 Springer-Verlag. Received January 18, 1985. We thank David Stewart (USGS, Reston, Virginia), Roland Reed (EI Cajon, California), Gordon Brown (Stanford University, Stanford, California), Carl Francis (Harvard), Robert Reynolds (San Bernardino County Museum, California), and Simon Booth (The Zinc Corporation, Ltd., Broken Hill, Australia) for providing samples; Craig Martin, David Blair, and Sunney I. Chan (Caltech) for assistance and advice with EPR spectroscopy; James R. O'Neil and Robert E. Criss (USGS, Menlo Park, California) for the use of and instruction in running the hydrogen line in the stable isotope laboratory; John A. Weil for furnishing material in advance of publication. Comments from Gerhard Lehmann (Westfälische Wilhelms-U.), J.A. Weil (U. of Saskatchewan) and two anonymous reviewers substantially improved the manuscript. Financial support was provided by National Science Foundation grant EAR 7919987.
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Funding AgencyGrant Number
NSFEAR 7919987
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Caltech Division of Geological and Planetary Sciences3984
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ID Code:39545
Collection:CaltechAUTHORS
Deposited By: Tony Diaz
Deposited On:20 Sep 2013 23:31
Last Modified:20 Sep 2013 23:31

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