gsminmag Mineralogical Magazine Mineralogical Magazine 0026-461X Mineralogical Society 10.1180/minmag.1965.035.269.10 Xanthiosite and Aerugite Davis R. J. M.A., D.Phil. Hey M. H. M.A., D.Sc. Department of Mineralogy, British Museum (Natural History) Kingsbury A. W. G. F.G.S. Department of Mineralogy, University Museum, Oxford 3 1965 35 269 72 83 7 6 1963 Copyright © 1965, The Mineralogical Society 1965 Summary

Two nickel arsenates from South Terras mine, St. Stephen-in-Brannell, Cornwall, have been shown to be identical with the minerals xanthiosite and aerugite, described by C. Bergemann in 1858, and with two synthetic products described by J. B. Taylor and R. D. Heyding (1958). Xanthiosite is pure golden-yellow, monoclinic, with a 10·174, b 9·548, c 5·766 Å, β 92° 5812′, space group P21/a; with D415=5·42±0·10, the unit cell contains 4[Ni3(AsO4)2] (Dcalc 5·388±0·003). Aerugite is deep blue-green, monoclinic, with a 10·29, b 5·95, c 9·79 Å, β 110° 19′, space-group C2, Cm, or C2/m; the ideal unit cell formula is 2[Ni9As3O16], with one-sixth of the arsenic trivalent; the natural mineral has a lower Ni:As ratio, around 2·6. Both xanthiosite and aerugite are minerals new to Britain.