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Penberthycroftite, [Al6(AsO4)3(OH)9(H2O)5]·8H2O, a second new hydrated aluminium arsenate mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK

  • I. E. Grey (a1), J. Betterton (a2), A. R. Kampf (a3), C. M. Macrae (a1), F. L. Shanks (a4) and J. R. Price (a5)...


Penberthycroftite, ideally [Al6(AsO4)3(OH)9(H2O)5]·8H2O, is a new secondary aluminium arsenate mineral from the Penberthy Croft mine, St. Hilary, Cornwall, England, UK. It occurs as tufts of white, ultrathin (sub-micrometre) rectangular laths, with lateral dimensions generally < 20 μm. The laths are flattened on {010} and elongated on [100]. The mineral is associated with arsenopyrite, bettertonite, bulachite, cassiterite, chalcopyrite, chamosite, goethite, liskeardite, pharmacoalumite–pharmacosiderite and quartz. Penberthycroftite is translucent with a white streak and a vitreous to pearly lustre. The calculated density is 2.18 g/cm3. Optically, only the lower and upper refractive indices could be measured, 1.520(1) and 1.532(1) respectively. No pleochroism was observed. Electron microprobe analyses (average of 14) with H2O obtained from thermogravimetric analysis and analyses normalized to 100% gave Al2O3 = 31.3, Fe2O3 = 0.35, As2O5 = 34.1, SO3 = 2.15 and H2O = 32.1. The empirical formula, based on nine metal atoms and 26 framework anions is [Al5.96Fe0.04(As0.97Al0.03O4)3(SO4)0.26(OH)8.30(H2O)5.44](H2O)7.8, corresponding to the ideal formula [Al6(AsO4)3(OH)9(H2O)5]·8H2O. Penberthycroftite is monoclinic, space group P21/c with unit-cell dimensions (100 K): a = 7.753(2) Å, b = 24.679(5) Å, c = 15.679(3) Å and β = 94.19(3)°. The strongest lines in the powder X-ray diffraction pattern are [d obs in Å(I) (hkl)] 13.264(46) (011); 12.402(16)(020); 9.732(100)(021); 7.420(28)(110); 5.670(8)(130); 5.423(6)(1̄31). The structure of penberthycroftite was solved using synchrotron single-crystal diffraction data and refined to wR obs = 0.059 for 1639 observed (I> 3σ(I)) reflections. Penberthycroftite has a heteropolyhedral layer structure, with the layers parallel to {010}. The layers are strongly undulating and their stacking produces large channels along [100] that are filled with water molecules. The layers are identical to those in bettertonite, but they are displaced relative to one another along [001] and [010] such that the interlayer volume is decreased markedly (by ∼10%)relative to that in bettertonite, with a corresponding reduction in the interlayer water content from 11 H2O per formula unit (pfu) in bettertonite to 8 H2O pfu in penberthycroftite.


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Betterton, J. (2000) Famous mineral localities: Penberthy Croft mine, St. Hilary, Cornwall, England. UK Journal of Mines and Minerals, 20, 7—37.
Bevins, R.E., Young, B., Mason, J.S., Manning, D.A.C. and Symes, R.F. (2010). Mineralization of England and Wales. Geological Conservation Review Series, No 36. Joint Nature Conservation Committee, Peterborough, UK, pp. 496–99.
Bowell, R.J., Alpers, C.N., Jamieson, H.E., Nordstrom, D.K. and Majzlan, J. (editors) (2014) Arsenic: Environmental Geochemistry, Mineralogy, and Microbiology.Reviews in Mineralogy and Geochemistry, 79. Mineralogical Society of America and the Geochemical Society, Chantilly, Virginia, USA, 635 pp.
Cooper, M.A., Abdu, Y.A., Ball, N.A., Hawthorne, F.C., Back, M.E., Tait, K.T., Schlüter, J., Malcherek, T., Pohl, D. and Gebhard, G. (2012). Ianbruceite, ideally [Zn2(OH)(H2O)(AsO4)](H2O)2, a new arsenate mineral from the Tsumeb mine, Otjikoto (Oshikoto) region, Namibia: description and crystal structure. Mineralogical Magazine, 76, 11191131.
Farrugia, L.J. (2012) WinGX and ORTEP for Windows: an update. Journal of Applied Crystallography, 45, 849854.
Frost, R.L., Scholz, R. and Lopez, A. (2015) Raman and spectroscopic characterization of the arsenate-bearing mineral tangdanite and in comparison with the discredited mineral clinotyrolite. Journal of Raman Spectroscopy, 46, 920926.
Gao, Q., Li, F., Wang, Y., Xu, L., Bai, J. and Wang, Y. (2014) Organic functionalization of polyoxometalate in aqueous solution: self-assembly of a new building block of ﹛VMo6O25﹜ with triethanolamine. Dalton Transactions, 43, 941944.
Grey, I.E., Mumme, W.G., MacRae, C.M., Caradoc-Davies, T., Price, J.R., Rumsey, M.S. and Mills, S.J. (2013) Chiral edge-shared octahedral chains in liskear-dite, [(Al,Fe)32(AsO4)18(OH)42(H2O)22]-52H2O, an open framework mineral with a pharmacoalumite-related structure. Mineralogical Magazine, 77,31253135.
Grey, I.E., Kampf, A.R., Price, J.R. and MacRae, C.M. (2014a) Bettertonite, IMA 2014-074. CNMNC Newsletter No. 23, February 2015, page 55; Mineralogical Magazine, 79, 51—58.
Grey, I.E., Mumme, W.G., Price, J.R., Mills, S.J., MacRae, C.M. and Favreau, G. (2014b) Ba-Cu ordering in bariopharmacoalumite-Q2a2b2c from Cap Garonne, France. Mineralogical Magazine, 78, 851860.
Grey, I.E., Betterton, J., Kampf, A.R., Price, J.R. and MacRae, C.M. (2015a) Penberthycroftite, IMA 2015-025. CNMNC Newsletter No. 26, August 2015, page 943; Mineralogical Magazine, 79, 941947.
Grey, I.E., Kampf, A.R., Price, J.R. and MacRae, C.M. (2015b) Bettertonite, [Al6(AsO4)3(OH)9(H2O)5]-11H2O, a new mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK, with a structure based on polyoxometalate clusters. Mineralogical Magazine, 79, 18491858.
Laugier, J. and Bochu, B. (2000) LMGP-Program for the Interpretation of X-ray Experiments. INPG/ Laboratoire des Matériaux et du Génie Physique. St Martin d'Heres, France.
Libowitzky, E. (1999) Correlation of O-H stretching frequencies and O-H-0 hydrogen bond lengths in minerals. Pp. 103-115 in: Hydrogen Bond Researc.(P. Schuster and W Mikenda, editors). Springer-Verlag Wien.
Majzlan, J., Alpers, C.N., Koch, C.B., McCleskey, R.B., Myneni, S.C.B. and Neil, J.M. (2011) Vibrational, X-ray absorption, and Mossbauer spectra of sulphate minerals from the weathered massive sulphide deposit at iron Mountain, California. Chemical Geology, 284, 296305.
Mandarino, J.A. (1981) The Gladstone-Dale relationship: Part IV The compatibility concept and its application. The Canadian Mineralogist, 19, 441450.
Nakamoto, K. (1970) Infrared Spectra of Inorganic and Coordination Compounds. Wiley-Interscience, New York, 338 pp.
Petricek, Vand Dušek, M. (2006) JANA2006. Structure Determinations Software Programs.Institute of Physics, Academy of Sciences of the Czech Republic, Prague.
Sheldrick, G.M. (2008) A short history of SHELX. Acta Crystallographica, A64, 112—122.
Taylor, R. (2011) Gossans and Leached Cappings Field Assessment. Springer Verlag, Heidelberg, Germany, 146pp.
Vansant, F.K., van der Veken, B.J. and Dessyn, H.O. (1973) Vibrational analysis of arsenic acid and its anions. 1. Description of the Raman spectra. Journal of Molecular Structure, 15, 425–4-37.
Visser, J.W.(1969) A fully automated program for finding the unit cell from powder data. Journal of Applied Crystallography, 2, 89.
Walenta, K (1983) Bulachit, ein neues Aluminiumarsenatmineral von Neubulach im nordli-chen Schwarzwald. Aufschluss, 34, 445—451.

Penberthycroftite, [Al6(AsO4)3(OH)9(H2O)5]·8H2O, a second new hydrated aluminium arsenate mineral from the Penberthy Croft mine, St. Hilary, Cornwall, UK

  • I. E. Grey (a1), J. Betterton (a2), A. R. Kampf (a3), C. M. Macrae (a1), F. L. Shanks (a4) and J. R. Price (a5)...


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