Wilancookite, (Ba,K,Na)8(Ba,Li,[])6Be24P24O96·32H2O, a new 2 beryllophosphate with a zeolite framework.

Abstract

Wilancookite, ideally (Ba,K,Na)8(Ba,Li,[])6Be24P24O96·32H2O, is a new mineral species from the Lavra Ponte do Piauí 19 complex granitic pegmatite, Minas Gerais, Brazil. It occurs as tiny dodecahedral {1 1 0} crystals, deposited on moraesite fibres. 20 Associated primary minerals are albite, montebrasite, Li-bearing micas, cassiterite, elbaite and quartz, while the secondary phosphate 21 association contains fluorapatite, childrenite, eosphorite, zanazziite, greifenstenite, guimarãesite, ushkovite, saléeite and moraesite. 22 The mineral is transparent and colourless, with a vitreous lustre; it is non-fluorescent, brittle, and its streak is white. The estimated 23 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) 24 (measured under l = 590nm). Electron- and ion-microprobe analyses give (in wt%): P2O5 36.19, SiO2 0.04, Al2O3 0.41, BaO 25 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 26 on the basis of 96 anhydrous oxygen atoms, is (Ba7.54K0.32Na0.14)S8.00(Ba3.04Li1.57[]1.39)S6.00Be24.08(P23.88Al0.38Si0.03)S24.29 27 O96·32H2O. The single-crystal unit-cell parameters are a = 13.5398(2)A

and V = 2482.21(7), space group I23. The eight strongest 28 lines in the powder X-ray diffraction pattern [d(in A

)(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) 29 (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 30 has been refined, based on single-crystal X-ray diffraction data, to R1 = 4.58%; the beryllophosphate framework is similar to that 31 occurring in pahasapaite, and is based on zeolite-RHO cages. The mineral species and name were approved by the Commission on 32 New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA2015-034).