Wilancookite, (Ba,K,Na)8(Ba,Li,[])6Be24P24O96·32H2O, a new beryllophosphate with a zeolite framework

Authors: Frédéric Hatert 1, Simon Philippo 2, Luisa Ottolini 3, Fabrice Dal Bo 1, Ricardo Scholz 4, Mário L.S.C. Chaves 5, Hexiong Yang 6, Robert T. Downs 6, Luiz A.D. Menezes Filho 7

1 Laboratoire de Minéralogie, B18, Université de Liège, Belgium
2 Section Minéralogie, Musée national d’histoire naturelle, Luxembourg
3 C.N.R. – Istituto di Geoscienze e Georisorse (IGG), Pavia, Italy
4 Universidade Federal de Ouro Preto (UFOP), Escola de Minas, Departamento de Geologia, Ouro Preto, MG, Brazil
5 Universidade Federal de Minas Gerais (UFMG), Instituto de Geociências, Belo Horizonte, MG, Brazil
6 Department of Geosciences, Gould-Simpson Building, University of Arizona, Tuscon, USA
7  Belo Horizonte, MG, Brazil

Source: Hatert, F., S. Philippo, L. Ottolini, F. Dal Bo, R. Scholz, M.L.S.C. Chaves, H. Yang, R. T. Downs, L. A.D. Menezes Filho, 2017. – Wilancookite, (Ba,K,Na)8(Ba,Li,[])6Be24P24O96·32H2O, a new beryllophosphate with a zeolite framework. – European Journal of Mineralogy. –

Abstract: Wilancookite, ideally (Ba,K,Na)8(Ba,Li,[])6Be24P24O96·32H2O, is a new mineral species from the Lavra Ponte do Piauí complex granitic pegmatite, Minas Gerais, Brazil. It occurs as tiny dodecahedral {1 1 0} crystals, deposited on moraesite fibres. Associated primary minerals are albite, montebrasite, Li-bearing micas, cassiterite, elbaite and quartz, while the secondary phosphate association contains fluorapatite, childrenite, eosphorite, zanazziite, greifenstenite, guimarãesite, ushkovite, saléeite and moraesite. The mineral is transparent and colourless, with a vitreous lustre; it is non-fluorescent, brittle, and its streak is white. The estimated Mohs hardness is 4–5, and the calculated density is 3.05 g/cm3. Wilancookite is isotropic, colourless, non-pleochroic, with n = 1.560(2) (measured under λ = 590 nm). Electron- and ion-microprobe analyses give (in wt%): P2O5 36.19, SiO2 0.04, Al2O3 0.41, BaO 34.65, Na2O 0.09, K2O 0.32, BeO 12.86, Li2O 0.50, and H2Ocalc 12.31, total 97.37 wt%. The resulting empirical formula, calculated on the basis of 96 anhydrous oxygen atoms, is (Ba7.54K0.32Na0.14)∑8.00(Ba3.04Li1.57[]1.39)∑6.00Be24.08(P23.88Al0.38Si0.03)∑24.29 and O96·32H2O. The single-crystal unit-cell parameters are a = 13.5398(2) Å and V = 2482.21(7), space group I23. The eight strongest lines in the powder X-ray diffraction pattern [d(in Å)(I)(hkl)] are: 6.90(60)(2 0 0), 5.54(80)(2 1 1), 3.630(60)(3 2 1, 3 1 2), 3.212(70) (3 3 0, 4 1 1), 3.043(100)(4 2 0, 4 0 2), 2.885(70)(3 3 2), 2.774(80)(4 2 2), and 2.398(60)(4 4 0). The crystal structure of wilancookite has been refined, based on single-crystal X-ray diffraction data, to R1 = 4.58%; the beryllophosphate framework is similar to that occurring in pahasapaite, and is based on zeolite-RHO cages. The mineral species and name were approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2015-034).

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