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A spectroscopic study of irradiation coloring of amazonite: structurally hydrous, Pb-bearing feldspar

Hofmeister, Anne M. and Rossman, George R. (1985) A spectroscopic study of irradiation coloring of amazonite: structurally hydrous, Pb-bearing feldspar. American Mineralogist, 70 (7-8). pp. 794-804. ISSN 0003-004X.

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Irradiation-induced color in amazonite can develop only in potassium feldspar having both structurally bound H_2O and Pb impurities. Amazonite color is controlled by either (1) an absorption minimum in the β spectrum between three overlapping bands in the ultraviolet and a broad band at 625 to 643 nm, resulting in a blue color, (2) a combination in β of one UV band and a broad band at 720 nm, resulting in a green color, or (3) both of the above superimposed, resulting in a blue-green color. All optical variations correlated with an EPR pattern indicative of Pb^(3+) or Pb^(1+). The different types of color are associated with a limited range in Pb content and structural state. For constant Pb content, the intensity of color is linearly related to the amount of structurally bound H_2O, up to a limiting value. Dependence of color intensity on both Pb and H_2O concentration strongly suggests that lead and water occur in a 1 :1 ratio in the color centers. The first order reaction kinetics of amazonite color formation by irradiation and the observation that water is not consumed in the process suggests that water plays a catalytic role in the irradiative transformation of Pb^(2+) to the amazonite chromophore.

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Rossman, George R.0000-0002-4571-6884
Additional Information:© 1985 Mineralogical Society of America. Manuscript received, Apri/12, 1984; accepted for publication, March 14, 1985. Special thanks are due to E. E. Foord (U.S.G.S., Denver) for generously sharing his samples and research ideas with us. Samples were also donated by S. Booth (Zinc Corp. Ltd., Broken Hill, Australia), G. Brown (Stanford), R. Cubba and S. Rigden (Caltech), R. Currier (Jewel Tunnel Imports, Arcadia, California), S. Ghose and A. Irving (U. of Washington), and R. Reynolds (San Bernardino County Museiun, California). We thank S. Chan, C. Martin, and D. Blair (Caltech Chemistry Division) for assistance and advice with EPR spectroscopy. Thanks are due to J. R. O'Neil and R. E. Criss (U.S.G.S., Menlo Park) for assistance with hydrogen manometry there. Discussions with L. T. Silver (Caltech) were very helpful. Critical review by E. E. Foord (U.S.G.S., Denver), S. Ghose (U. Washington), G. Lehmann (Muenster), R. F. Martin (McGill U.), and J. Weil (U. Saskatchewan) substantially improved the manuscript. This work was supported in part by NSF grants EAR-79-19987, 79-04801, and 83-13098.
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NSFEAR 79-04801
NSFEAR 83-13098
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Caltech Division of Geological and Planetary Sciences4050
Issue or Number:7-8
Record Number:CaltechAUTHORS:20130514-105135844
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Official Citation: Anne M. Hofmeister and George R. Rossman A spectroscopic study of irradiation coloring of amazonite; structurally hydrous, Pb-bearing feldspar American Mineralogist, August 1985, v. 70, p. 794-804
Usage Policy:No commercial reproduction, distribution, display or performance rights in this work are provided.
ID Code:38495
Deposited By: Ruth Sustaita
Deposited On:14 May 2013 18:06
Last Modified:26 Nov 2019 11:15

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