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Kernowite, Cu2Fe(AsO4)(OH)4⋅4H2O, the Fe3+-analogue of liroconite from Cornwall, UK

Published online by Cambridge University Press:  12 May 2021

Michael S. Rumsey Open the ORCID record for Michael S. Rumsey [Opens in a new window] ,
Mark D. Welch ,
John Spratt ,
Annette K. Kleppe  and
Martin Števko
Michael S. Rumsey*
Affiliation:
Department of Earth Sciences, Natural History Museum, LondonSW7 5BD, UK
Mark D. Welch
Affiliation:
Department of Earth Sciences, Natural History Museum, LondonSW7 5BD, UK
John Spratt
Affiliation:
Core Research Laboratories, Natural History Museum, LondonSW7 5BD, UK
Annette K. Kleppe
Affiliation:
Diamond Lightsource UK, Harwell Science Park, Chilton, OxfordshireOX11 0DE, UK
Martin Števko
Affiliation:
Earth Science Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 840 05 Bratislava, Slovak Republic Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Praha, Horní Počernice, Czech Republic
*
*Author for correspondence: Michael S. Rumsey, Email: [email protected]
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Abstract

The occurrence, chemical composition and structural characterisation of the new mineral kernowite, ideally Cu2Fe(AsO4)(OH)4⋅4H2O, the Fe3+-analogue of liroconite, Cu2Al(AsO4)(OH)4⋅4H2O, are described. Kernowite (IMA2020-053) occurs on specimens probably sourced from the Wheal Gorland mine, St Day, Cornwall, UK, in the cavities of a quartz-gossan rich in undifferentiated micro-crystalline grey sulfides and poorly crystalline arsenic phases including both pharmacosiderite and olivenite-group minerals. The average composition of kernowite determined from several holotype fragments by electron microprobe analysis is Cu1.88(Fe0.79Al0.09)Σ0.88(As1.12O4)(OH)4⋅3.65H2O. The structure of kernowite has been determined in monoclinic space group I2/a (a non-standard setting of C2/c) by single-crystal X-ray diffraction (SCXRD) to R1 = 0.025, wR2 = 0.051 and Goodness-of-fit = 1.112. Unit-cell parameters from SCXRD are a = 12.9243(4) Å, b = 7.5401(3) Å, c = 10.0271(3) Å, β = 91.267(3)°, V = 976.91(6) Å3 and Z = 4. The chemical formula of this crystal indicated by SCXRD from refined site-scattering is Cu2(Fe3+0.84(1)Al0.16)AsO4(OH)4⋅4H2O. The network of hydrogen bonding has been determined and is similar to that reported for liroconite from Wheal Gorland by Plumhoff et al. (2020).

Keywords

kernowiteliroconiteCornwalliron aluminium arsenatemineral collectionsmineral museumUnited Kingdomnew mineral
Type
Article
Information
Mineralogical Magazine , Volume 85 , Issue 3 , June 2021 , pp. 283 - 290
Copyright
Copyright © The Author(s), 2021. Published by Cambridge University Press on behalf of The Mineralogical Society of Great Britain and Ireland

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Footnotes

Associate Editor: Juraj Majzlan

References

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