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HAINEAULTITE, A NEW HYDRATED SODIUM CALCIUM TITANOSILICATE FROM MONT SAINT-HILAIRE, QUEBEC: DESCRIPTION, STRUCTURE DETERMINATION AND GENETIC IMPLICATIONS

Andrew M. McDonald^1, and George Y. Chao^2,¶

¹ Department of Earth Sciences, Laurentian University, Sudbury, Ontario P3E 2C6, Canada
² Ottawa–Carleton Geoscience Centre, Department of Earth Sciences, Carleton University, Ottawa Ontario K1S 5B6, Canada

E-mail address: amcdonald{at}nickel.laurentian.ca

Haineaultite, ideally (Na,Ca)₅Ca(Ti,Nb)₅(Si,S)₁₂O₃₄(OH,F)₈·5H₂O, is a new mineral species found predominantly in altered marble xenoliths at the Poudrette quarry, Mont Saint-Hilaire, Quebec. The mineral arose through the interaction of incompatible-element-rich late-stage fluids with marble xenoliths. At least some marble xenoliths were derived from limestones of Silurian, rather than Grenvillian, age. Crystals of haineaultite are generally lemon-yellow and more rarely tan, off-white or pale orange. The mineral occurs as either isolated, prismatic crystals, or fan-like aggregates of more tabular crystals, elongate along [001], with a maximum length of 6 mm. Associated minerals include pectolite, fluorapophyllite, vesuvianite, tainiolite, albite (pink), fluorite, calcite, microcline, aegirine and, to a lesser extent, analcime, steacyite, monteregianite-(Y), leucosphenite, mangan-neptunite, ancylite-(Ce), an alkali amphibole, a eudialyte-group mineral, sodalite, stillwellite-(Ce), vinogradovite, götzenite, pyrite, molybdenite, galena, sphalerite, and hibschite. The mineral has a vitreous luster, is transparent to translucent, has a white streak and shows no fluorescence in either short- or long-wave ultraviolet radiation. It has a Mohs hardness of 3 to 4, with distinct to good cleavages on {100}, {010} and {001}. It is brittle with a blocky to splintery fracture. The calculated density is 2.28 g/cm³. Haineaultite is optically biaxial (+), with 1.599(1), ß 1.610(1), 1.696(1), 2V_meas = 38(1)°, 2V_calc = 41(1)°, and non-pleochroic. The optical orientation is X = b, Y = c and Z = a. Sixteen electron-microprobe analyses gave, on average, Na₂O 4.70, K₂O 2.09, MgO 0.07, CaO 9.99, MnO 0.25, FeO 0.49, SiO₂ 42.70, TiO₂ 18.86, ZrO₂ 0.31, Nb₂O₅ 5.56, SO₃ 2.60, F 0.17 and H₂O (calc.) 10.11, O=F –0.07, total 97.83 wt.%. The principal absorptions in the infrared include 3392, 1620, 1100, 985, 900, 720, 470 cm^–1, indicative of both OH and H₂O in the structure. The mineral is orthorhombic, space group C222, a 7.204(2), b 23.155(5), c 6.953(2) Å, V 1159.8(1) ų, Z = 1. The strongest seven lines in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are: 11.564(100)(020), 6.932(90)(001,110), 3.052(75)(240), 2.977(70)(042), 5.258(40)(130), 4.446(40)(041), and 2.582(40)(152,062). The structure of haineaultite was refined to R = 5.41%, wR² = 18.50%. It consists of eight-membered (8MR) rings of SiO₄ tetrahedra, linked to adjacent rings to form vierer double chains along [001], which are cross-linked by TiO₆ octahedra to produce a mixed tetrahedron–octahedron titanosilicate framework similar to that found in zorite. Channels running parallel to [100] are occupied by Ca and H₂O, with Na occupying channels parallel to [001]. The mineral possesses an OD structure, exemplified by disordering of both framework and interframework ions. Haineaultite bears a relationship to technologically important synthetic microporous titanosilicates such as ETS–4 and ETS–10.

Keywords: haineaultite, new mineral species, microporous, titanosilicate, crystal structure, Mont Saint-Hilaire, Quebec.

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