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Hydroniumpharmacosiderite, a new member of the pharmacosiderite supergroup from Cornwall, UK: structure and description

Published online by Cambridge University Press:  05 July 2018

S. J. Mills ,
A. R. Kampf ,
P. A. Williams ,
P. Leverett ,
G. Poirier ,
M. Raudsepp  and
C. A. Francis
S. J. Mills*
Affiliation:
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver BC, Canada V6T 1Z4
A. R. Kampf
Affiliation:
Mineral Sciences Department, Natural History Museum of Los Angeles County, 900 Exposition Boulevard, Los Angeles, California 90007, USA
P. A. Williams
Affiliation:
School of Natural Sciences, University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW 1797, Australia
P. Leverett
Affiliation:
School of Natural Sciences, University of Western Sydney, Locked Bag 1797, Penrith South DC, NSW 1797, Australia
G. Poirier
Affiliation:
Mineral Sciences Division, Canadian Museum of Nature, PO Box 3443, Station D, Ottawa, Ontario, Canada K1P 6P4
M. Raudsepp
Affiliation:
Department of Earth and Ocean Sciences, University of British Columbia, Vancouver BC, Canada V6T 1Z4
C. A. Francis
Affiliation:
Harvard Mineralogical Museum, 24 Oxford Street, Cambridge, Massachusetts 02138, USA
*
*E-mail: smills@eos.ubc.ca
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Abstract

Hydroniumpharmacosiderite, ideally (H3O)Fe4(AsO4)3(OH)4·4H2O, is a new mineral from Cornwall, UK, probably from the St. Day group of mines. It occurs as a single yellowish green, slightly elongated cube, measuring 0.17 mm ×0.14 mm ×0.14 mm. The mineral is transparent with a vitreous lustre. It is brittle with a cleavage on {001}, has an irregular fracture, a white streak and a Mohs hardness of 2–3 (determined on H3O-exchanged pharmacosiderite). Hydroniumpharmacosiderite has a calculated density of 2.559 g cm–3 for the empirical formula. The empirical formula, based upon 20.5 oxygen atoms, is: [(H3O)0.50K0.48Na0.06]1.04(Fe3.79Al0.22)4.01[(As2.73P0.15)2.88O12](OH)4·4H2.14O. The five strongest lines in the X-ray powder diffraction pattern are [dobs(Å),Iobs,(hkl)]: 8.050,100,(001); 3.265,35,(112); 2.412,30,(113); 2.830,23,(202); 4.628,22,(111). Hydroniumpharmacosiderite is cubic, space group with a = 7.9587(2) Å, V = 504.11(2) Å3 and Z = 1. The crystal structure was solved by direct methods and refined to R1 = 0.0481 for 520 reflections with I > 2σ(I). The structure is consistent with determinations for H3O-exhchanged pharmacosiderite and the general pharmacosiderite structure type.

Keywords

hydroniumpharmacosideritecrystal structureCornwallnew mineralhydroniumpharmacosideriteUK
Type
Research Article
Information
Mineralogical Magazine , Volume 74 , Issue 5 , October 2010 , pp. 863 - 869
Copyright
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

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