Home > Mineral Abstracts > CanMin Vol. 42, pp. 769-780 (2004)




Vol. 42, pp. 769-780 (2004)



Haineaultite, a new hydrated
sodium calcium titanosilicate
from Mont Saint-Hilaire, Quebec:
description, structure determination
and genetic implications


Andrew M. McDonald, and George Y. Chao


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), 2Vmeas = 38(1)°, 2Vcalc = 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

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) Å3, 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)

 
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.


© 2004  The Canadian Mineralogist