Home > Mineral Abstracts > CanMin Vol. 42, pp. 781 -785 (2004)




Vol. 42, pp. 781 -785 (2004)



Manganokukisvumite, a new mineral species from mont Saint-Hilaire, Quebec


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


ABSTRACT

     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 5½ to 6. It is sectile, slightly flexible, with no apparent cleavage but with a splintery fracture.

     Manganokukisvumite is biaxial negative, α(calc.) 1.657, β 1.744 ± 0.003 and γ 1.792 ± 0.003 (for λ = 589 nm); 2Vmeas 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)
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:


(Na5.81K0.05Ca0.02Ce0.01)Σ5.89 (Mn0.89Fe0.09Mg0.07Al0.04)Σ1.09


(Ti3.88Nb0.06)Σ3.94Si8.01O28 · 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.

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



© 2004  The Canadian Mineralogist