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MANGANOKUKISVUMITE, A NEW MINERAL SPECIES FROM MONT SAINT-HILAIRE, QUEBEC

Robert A. Gault, T. Scott Ercit, Joel D. Grice and Jerry Van Velthuizen

Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada

E-mail address: rgault{at}mus-nature.ca

Manganokukisvumite, ideally Na₆MnTi₄Si₈O₂₈·4H₂O, is a new mineral species from the Poudrette Quarry, Mont Saint-Hilaire, Rouville County, Quebec (IMA 2002–029). It occurs in small cavities in an albite-rich syenite breccia associated with aegirine, microcline, albite, annite, chalcopyrite, pyrite, pyrrhotite, natrolite, labuntsovite-Mn, titanite, calcite, a chlorite-group mineral, magnetite, fluorapatite, elpidite and sodalite. Manganokukisvumite crystals are colorless and transparent with a vitreous luster and a white streak. It is non-fluorescent in short- and long-wave ultraviolet light. The crystals are extremely thin, flattened and sword-shaped to 0.5 mm in length, commonly forming rosette-like radiating groups. Forms observed are pinacoids {100} and {010} and a prism that we could not measure. No twinning was observed. The hardness is 5 to 6. It is sectile, slightly flexible, with no apparent cleavage but with a splintery fracture. Manganokukisvumite is biaxial negative, (calc.) 1.657, ß 1.744 0.003 and 1.792 0.003 (for = 589 nm); 2V_meas 70° (Kamb’s method). There is no dispersion or pleochroism; the optical orientation is X = a, Y = b and Z = c. It is orthorhombic, space group Pccn, with unit-cell parameters refined from powder data: a 29.05(2), b 8.612(6), c 5.220(4) Å, V 1305.9(3) A³ and Z = 2. The strongest X-ray powder-diffraction lines [d in Å(I)(hkl)] are: 14.47(100)(200), 6.43(20)(310), 4.83(10)(600), 3.743(10)(710), 3.025(40)(910), 2.881(20)(521), 2.591(10)(721), 2.458(10)(402) and 2.146(10)(930). An electron-microprobe analysis supported by infrared-absorption spectrometry gave Na₂O 15.61, K₂O 0.21, MgO 0.26, CaO 0.08, MnO 5.48, FeO 0.57, Al₂O₃ 0.16, Ce₂O₃ 0.18, SiO₂ 41.74, TiO₂ 26.90, Nb₂O₅ 0.68, H₂O 6.25 (calculated by stoichiometry), total 98.12 wt.%. The empirical formula based on O = 32, is: (Na_5.81K_0.05Ca_0.02Ce_0.01)_5.89 (Mn_0.89Fe_0.09Mg_0.07Al_0.04)_1.09(Ti_3.88Nb_0.06)_3.94Si_8.01O₂₈·4H₂O or, ideally, Na₆MnTi₄Si₈O₂₈·4H₂O. The calculated density (from the empirical formula) is 2.88 g/cm³, and the measured density is 2.86(1) g/cm³. A Gladstone–Dale calculation gives a compatibility index of 0.038 (excellent). Manganokukisvumite is the manganese-dominant analogue of kukisvumite and is closely related to lintisite.

Keywords: manganokukisvumite, new mineral species, Mont Saint-Hilaire, Quebec.

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