Home > Mineral Abstracts > CanMin Vol. 18, pp. 497-502 (1980)




Vol. 18, pp. 497-502 (1980)



Petarasite, a new hydrated sodium zirconium hydroxychlorosilicate mineral from
Mont St-Hilaire, Quebec


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



T. T. Chen
CANMET, 555 Booth Street,
Ottawa, Ontario K1A 0G1



Judith Baker
Department of Geology, Carleton University,
Ottawa, Ontario K1P 6P4


ABSTRACT

     The new mineral petarasite occurs as irregular grains in a xenolith in the nepheline syenite at Mont St-Hilaire, Quebec.  The xenolith is composed predominantly of biotite and microcline with minor amounts of catapleiite, apatite, zircon and other accessory minerals.  The mineral is monoclinic, P21/m,a 10.791(4), b 15.505(5), c 6.626(2) Å, b 113.21(3)°.  The strongest eight lines of the X-ray diffraction pattern [dhkl (I)(hkl)] are:


7.25 (70)(020)
6.09 (40)(001)
4.96 (15)(200)
4.10 (100)(220)

3.220 (30)
(310, 202, 112)
3.041 (30)(002)
2.924 (100)
(240, 241)
1.729 (20)
(551, etc.)


     The mineral is greenish-yellow with white streak, transparent to translucent with vitreous lustre.  It has perfect {110}, very good {010} and distinct {001} cleavages.  Hardness 5-5½; fracture subconchoidal.  Density 2.88(1) (meas.), 2.915 g/cm3 (calc.).  Optically, the mineral is biaxial (+), a 1.596(1), b 1.598(1), g 1.632(1) (in Na light), 2V meas 29°, calc 27.7°.   Dispersion weak r < v.  Pleochroism:  X colorless, Y = Z pale greenish yellow.  Absorption formula:  X < Y = Z.  Orientation:  X = b, Z & c = +41.5°.


     Electron-microprobe analyses correspond to:


(Na4.69Ca0.13K0.05)(Zr2.01Ti0.01)Si6O18[OH)0.60Cl0.48] · 3.01 H2O,


whereas the ideal structural formula is Na5Zr2Si6O18 · 2 H2O, Z = 2.


     Excess water shown in the empirical formula is due to absorbed water.  TGA and DTG show two stages of weight loss at 25-830 and 830-1100° C.  The mineral decomposes to parakeldyshite after heating to 1100° C.  Infrared absorption spectra confirm the presence of structural and absorbed water.

Keywords:  new mineral, hydrated, sodium, zirconium, hydroxychlorosilicate, Mont St-Hilaire, Quebec.


© 1980  The Canadian Mineralogist