ABSTRACT

     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 a 1.599(1), ß 1.610(1), g 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:

O F - 0.07

     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) Å3, Z = 1. The strongest seven lines in the X-ray powder-diffraction pattern [d in Å(I)(hkl)] are:

     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.