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


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.

Research Article
Copyright © The Mineralogical Society of Great Britain and Ireland 2010

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