Kernowite, Cu2fe(Aso4)(OH)4⋅4H2O, the Fe -Analogue of Liroconite from Cornwall, UK
Mineralogical Magazine (2021), 85, 283–290 doi:10.1180/mgm.2021.40 Article 3+ Kernowite, Cu2Fe(AsO4)(OH)4⋅4H2O, the Fe -analogue of liroconite from Cornwall, UK Michael S. Rumsey1* , Mark D. Welch1, John Spratt2, Annette K. Kleppe3 and Martin Števko4,5 1Department of Earth Sciences, Natural History Museum, London SW7 5BD, UK; 2Core Research Laboratories, Natural History Museum, London SW7 5BD, UK; 3Diamond Lightsource UK, Harwell Science Park, Chilton, Oxfordshire OX11 0DE, UK; 4Earth Science Institute, Slovak Academy of Sciences, Dúbravská cesta 9, 840 05 Bratislava, Slovak Republic; and 5Department of Mineralogy and Petrology, National Museum, Cirkusová 1740, 193 00 Praha, Horní Počernice, Czech Republic Abstract ⋅ The occurrence, chemical composition and structural characterisation of the new mineral kernowite, ideally Cu2Fe(AsO4)(OH)4 4H2O, 3+ ⋅ the Fe -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 compos- ition 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.
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