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

Frédéric Hatert, Simon Philippo, Luisa Ottolini, Fabrice Dal Bo, Ricardo Scholz, Mário L.S.C. Chaves, Hexiong Yang, Robert T Downs, Luiz A.D. Menezes Filho

Research output: Contribution to journalArticle

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 = 590nm). 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 97.37wt%. The resulting empirical formula, calculated on the basis of 96 anhydrous oxygen atoms, is (Ba7.54K0.32Na0.14)∑8.00(Ba3.04Li1.571.39)∑6.00Be24.08(P23.88Al0.38Si0.03)S24.29 O9632H2O. The single-crystal unit-cell parameters are a = 13.5398(2)Å and V = 2482.21(7)A- 3, 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).

Original languageEnglish (US)
Pages (from-to)923-930
Number of pages8
JournalEuropean Journal of Mineralogy
Volume29
Issue number5
DOIs
StatePublished - Jan 1 2017

Keywords

  • Beryllophosphate
  • Brazil
  • Crystal structure
  • Minas Gerais
  • New mineral
  • Pegmatite
  • Wilancookite
  • Zeolite framework

ASJC Scopus subject areas

  • Geochemistry and Petrology

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    Hatert, F., Philippo, S., Ottolini, L., Dal Bo, F., Scholz, R., Chaves, M. L. S. C., Yang, H., Downs, R. T., & Menezes Filho, L. A. D. (2017). Wilancookite, (Ba, K, Na)8(Ba, Li, □)6Be24P24O96 32H2O, a new beryllophosphate with a zeolite framework. European Journal of Mineralogy, 29(5), 923-930. https://doi.org/10.1127/ejm/2017/0029-2661