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Iowaite, a re-investigation

Published online by Cambridge University Press:  05 July 2018

R. S. W. Braithwaite
Affiliation:
Chemistry Department, University of Manchester Institute of Science and Technology, Manchester M60 1QD, U.K.
P. J. Dunn
Affiliation:
Department of Mineral Sciences, Smithsonian Institution, Washington, D.C., 20560, U.S.A.
R. G. Pritchard
Affiliation:
Chemistry Department, University of Manchester Institute of Science and Technology, Manchester M60 1QD, U.K.
W. H. Paar
Affiliation:
Institüt für Mineralogie der Universitat Salzburg, Hellbrunnerstrasse 34/III, A-5020 Salzburg, Austria

Abstract

Iowaite has been re-examined using new, well crystallized material from the Palabora open pit mine, Transvaal. Microprobe, carbon analyser and thermal analyses, powder and single-crystal X-ray diffraction, infrared, UV-visible and mass spectroscopic and optical studies were made. The ideal formula is (OH)16Cl2·4H2O. It is trigonal, Rm, a = 3.1183(9), c = 24.113(8) Å, V = 203.1(2) Å3, Z = 3/8; Dobs 2.09 g/cm3.; Dcalc 2.04 g/cm3; hardness (Mohs)=2 1/2. The interlayer Cl ions are displaced from the threefold axis. It is uniaxial negative, with ω = 1.561 ± 0.002, ε = 1.543 ± 0.002; coloured crystals are intensely pleochroic, due to intervalence charge transfer between the Fe3+ and Fe2+ substituting for Mg2+, with O pale yellow, E deep blue-green.

Type
Crystal Structure
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 1994

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