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Licensed Unlicensed Requires Authentication Published by De Gruyter February 9, 2017

Kegginite, Pb3Ca3[AsV12O40(VO)]·20H2O, a new mineral with a novel ε-isomer of the Keggin anion

Anthony R. Kampf, John M. Hughes, Barbara P. Nash and Joe Marty
From the journal American Mineralogist

Abstract

Kegginite, Pb3Ca3[AsV12O40(VO)]·20H2O, is a new mineral species from the Packrat mine, near Gateway, Mesa County, Colorado, U.S.A. It is a secondary mineral found on asphaltum in a montroseite- and corvusite-bearing sandstone. Other secondary minerals found in close association with kegginite are ansermetite, gypsum, mesaite, and sherwoodite. Crystals of kegginite are orange-red simple hexagonal tablets. The streak is pinkish-orange, the luster is vitreous, the Mohs hardness is about 2, the tenacity is brittle, fracture is irregular, cleavage is good on {001}, and the calculated density is 2.69 g/cm3. Kegginite is optically uniaxial (–) with pleochroism: O orange-red and E red-orange; E < O. Electron microprobe analyses yielded the empirical formula Pb2.98Ca2.39Mg0.56V13.05As0.95O61H40.15. Kegginite is trigonal, P3¯, with a = 14.936(5), c = 15.846(5) Å, V = 3061(2) Å3, and Z = 2. The crystal structure of kegginite (R1 = 0.064 for 1356 Fo > 4σF reflections) contains a [As5+V125+O40(VO)]12 polyoxometalate cluster, which is a mono-capped Keggin ε-isomer.

Acknowledgements

Reviewers Michael Schindler and Henrik Friis are thanked for constructive comments, which improved the manuscript. Editorial handling by Fernando Colombo is greatly appreciated. This study was funded, in part, by the John Jago Trelawney Endowment to the Mineral Sciences Department of the Natural History Museum of Los Angeles County and by grant NSF-MRI 1039436 from the National Science Foundation to J.M.H. Jim Fisher, General Mine Superintendent, Denison Mines, allowed us to obtain specimens for study.

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Received: 2016-4-28
Accepted: 2016-8-24
Published Online: 2017-2-9
Published in Print: 2017-2-1

© 2017 by Walter de Gruyter Berlin/Boston