Home > Mineral Abstracts > CanMin Vol. 12, pp. 237-240 (1974)



Vol. 12, pp. 237-240 (1974)



Hilairite, Na2ZrSi3O9 · 3H2O, a new mineral
from Mont St. Hilaire, Quebec


George Y. Chao, David H. Watkinson and T.T. Chen
Department of Geology, Carleton University,
Ottawa, Ontario K1S 5B6


ABSTRACT

     Hilairite occurs as small, very pale brown, transparent crystals in miarolitic cavities and as flesh-pink porcelain-like opaque crystals in altered pegmatites in nepheline syenite at Mont St. Hilaire, Quebec.  The most abundant associated minerals are analcime, natrolite, microcline, catapleiite, elpidite, aegirine and chlorite.

     Hilairite crystals are trigonal, bounded by {1120} and {0112}.   The space group is R32, R3m or R3m; a = 10.556 (1) and c = 15.851 (2) Å.  Multiple twinning by [2201]180° and [0001]180° is very common.  D(cal.) = 2.739 and D (meas.) = 2.724 g/cm3.  Hardness > 4.   No obvious cleavage was observed.  It is optically uniaxial negative with eD = 1.596 (1) and wD = 1.609 (1).

     Average electron microprobe analyses gave:

SiO2 - 42.08
Al2O3 - 0.03
ZrO2 - 29.72

TiO2 - 0.04
CaO - 0.20
MgO - 0.01

FeO - 0.03
MnO - 0.02
Na2O - 13.43

K2O - 0.52
H2O - 13.54 (by TGA to 1000°C)

    Total = 99.62%.  The analysis corresponds to
Na1.85K0.05Ca0.02Zr1.03Si2.99O9 · 3.21H2O or ideally Na2ZrSi3O9 · 3H2O.

     Water in hilairite is zeolitic in nature; on heating hilairite loses all of its water at 220° C and at least 95% of the original water is recovered on cooling from 855° C to room temperature.  Attempts at hydrothermal synthesis were unsucessful.



© 1974  The Canadian Mineralogist