Abstract

Bussyite-(Y), ideally (Y,REE,Ca)3(Na,Ca)6MnSi9Be5(O,OH,F)34, a new mineral species, was found in the Mont Saint-Hilaire quarry, Quebec, Canada. The crystals are transparent to translucent, dark brown, with a white streak and vitreous luster. Crystals are blocky to prismatic, sometimes radiating, up to 3 mm in size. The mineral is brittle with a perfect {1¯01} cleavage. Associated minerals include aegirine, analcime, calcite, cappelenite-(Y), catapleiite, charmarite-2H and -3T, fluorite, helvine, kupletskite, microcline, perraultite, sérandite, and tainiolite. Bussyite-(Y) is monoclinic, space group C2, with unit-cell parameters refined from X-ray powder-diffraction data: a 11.545(2), b 13.840(2), c 16.504(4) Å, β 95.87(2)º, V 2623.1(6) Å3, and Z = 4. Electron microprobe analysis gave the average composition and ranges, in wt.%: Na2O 8.21 (8.43–8.07), K2O 0.08 (0.10–0.05), BeO 9.75 (determined by structure refinement), CaO 5.25 (5.36–5.16), MnO 2.93 (3.20–2.57), BaO 0.03 (0.06–0.00), FeO 0.40 (0.60–0.25), Al2O3 0.29 (0.34–0.21), Y2O3 7.58 (7.79–7.37), La2O3 0.48 (0.60–0.40), Ce2O3 2.66 (3.09–2.37), Pr2O3 0.55 (0.64–0.40), Nd2O3 2.85 (2.93–2.81), Sm2O3 1.45 (1.58–1.23), Eu2O3 0.013 (0.17–0.12), Gd2O3 1.97 (2.21–1.57), Tb2O3 0.31 (0.40–0.25), Dy2O3 2.20 (2.46–1.81), Ho2O3 0.39 (0.48–0.33), Er2O3 0.93 (1.07–0.86), Tm2O3 0.16 (0.20–0.12), Yb2O3 0.46 (0.60–0.36), Lu2O3 0.01 (0.01–0.01), Nb2O5 0.20 (0.25–0.15), SiO2 39.62 (40.03–38.96), ThO2 2.21 (2.43–1.90), F 3.49 (3.66–3.39), Cl 0.03 (0.03–0.02), H2O 5.10 (determined by crystal-structure refinement), O = F + Cl –1.48, total 98.15. The empirical formula based on the crystal-structure analysis showing 34 anions is: 4{(Y0.874Nd0.221Ce0.211Dy0.154Gd0.142Sm0.108Er0.063Pr0.043La0.038Yb0.030Ho0.027Tb0.022Tm0.011Eu0.010Ca0.789Th0.105)Σ1[Na3.442Ca0.800K0.022]Σ6.055(Mn0.537Fe0.072)Σ0.899(Si8.567Be5.065 Al0.222)Σ13.724(O24.107OH5.893)Ʃ30(F2.386OH1.60.3Cl0.011)Σ4}. The structure was refined to an R1 index of 0.035 for 6531 unique, observed reflections. The structure has two chemically distinct layers parallel to (2¯01): (1) a layer of [(Si,Be)O4] tetrahedra and (2) a large cation Y-,Ca-, Mn-, Na-(O,F) polyhedral layer. Layers are cross-linked through shared O and F atoms. Significant amounts of OH are present, as indicated in the IR spectrum and crystal-structure analysis.

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