Home > Mineral Abstracts > Can Min Vol. 16, pp. 561-566 (1978)




Vol. 16, pp. 561-566 (1978)



Monteregianite, a new hydrous sodium potassium yttrium silicate mineral from
Mont Saint-Hilaire, Quebec


George Y. Chao
Department of Geology, Carleton University,
Ottawa , Ontario K1S  5B6


ABSTRACT

     The new mineral monteregianite occurs as needle-shaped crystals in radiating clusters and as groups of tabular crystals in miarolitic cavities, metamorphosed inclusions and rheomorphic breccias in the nepheline syenite at Mont St-Hilaire, Québec.  The mineral is orthorhombic, Bmab or B2ab, a 14.014 (4), b 23.910 (5), c 13.096 (2) Å.  A pronounced pseudocell with a and c halved has Pmmb, P2mb or Pm2b symmetry.  Strongest eight lines of the X-ray powder diffraction pattern are:

12.00 (100)(020)
7.03 (100)(200)
6.55 (40)(002)
6.02 (50)(220,040)

4.42 (100)(042)
3.405 (50)(062)
3.026 (50)(034,440)
2.873 (80)(044)


     The mineral is colorless, white, grey or rarely mauve or pale green with white streak and vitreous to silky lustre.  Crystals, varying in size from 0.05 to 3 mm, are bounded by {010}, {001} and {100}; some show additional {101}.  Cleavages:  {010} perfect, {001} very good and {100} fair.  Hardness 3½.  The mineral is readily etched by 1:1 HCl, HNO3 and H2SO4.  Optically, the mineral is biaxial positive, a 1.510 (1), b 1.513 (1), g 1.517 (1), 2V meas. 87°, calc. 82°, dispersion inconspicuous.  Orientation:  X = c,Y = a, Z = b.  Chemical analysis gave:

SiO2 60.30
Al2O3 0.50
Y2O3 11.97
   (probe analysis)
CaO 0.65


MgO 0.15
BaO 0.35
MnO n.d.
FeO n.d.

Na2O 9.14
K2O 5.36
H2O 11.40
   (TGA to 1000°C)
sum 99.82 wt. %

     corresponding to (Na4.66K1.80) (Y1.68Ca0.18Mg0.06Ba0.04)


(Si15.87All0.16) O38 · 10.02H2O or (Na,K)6 Y2Si16O38 · 10 H2O.


     Z = 4, D(meas.) 2.42, (calc.) 2.391 g/cm3.  TGA and DTG show three distinct stages of dehydration at 25-80, 80-200, and 200-400°º C.  Water in the mineral is zeolitic, and recovereable after heating to 650° C.  Infrared spectra confirm the presence of H2O in the mineral.


© 1978  The Canadian Mineralogist