Home > Mineral Abstracts > CanMin Vol. 29, pp. 355-358 (1991)




Vol. 29, pp. 355-358 (1991)



Perraultite, a new hydrous
Na-K-Ba-Mn-Ti-Nb silicate species from
Mont Saint-Hilaire, Quebec


George Y. Chao
Ottawa-Carleton Geoscience Centre, Department of Earth Sciences,
Carleton University, Ottawa, Ontario K1S 5B6


ABSTRACT

          Perraultite is a new mineral species from the De-Mix quarry, Mont Saint-Hilaire, Quebec.  It occurs as small prismatic crystals up to 0.5mm in pegmatite dikes in nepheline syenite associated with kupletskite, catapleiite, microcline, albite, aegirine, rhodochrosite, natrolite, tetranatrolite, lorenzenite, polyliothionite, ancylite, fluorite, calcite and pyrochlore.  The mineral is orange brown with a pale brown streak, vitreous, slightly waxy, opaque to translucent, transparent in small fragments, very brittle, and non-fluorescent in ultraviolet light.  Cleavage {001} very good; fracture uneven to irregular.  Mohs hardness about 4; D(meas) 3.71(5), D(calc) 3.808 g/cm3.  The mineral is not affected by HCl, H2SO4 and HNO3.  Optically biaxial (-), a 1.785(2), b 1.81(1), g 1.82(1) (l 589nm), 2V(meas.) 66(1)°,
2V(calc.) 64°, strong dispersion, r < v.1.570(1).  Orientation:  X = b,
Y & a = 19° in the obtuse b angle.   Pleochroism pronounced:  Z = dark brown, X = Y = light yellow.  Perraultite is monoclinic, C2/m, Cm or C2, a 10.820(2), b 13.843(4), c 20.93(1) Å, b 95.09(2)°, Z = 4.  An I2/m subcell with a' = ½a, b' = ½b, c' = c and b' =  is very pronounced.   Crystals are prismatic and flattened on {010}, with elongation along [100], bound by {001}, {010}, {100} and a {h0l} form, possibly {101}.   "Swallow-tail" contact twins are common, with {101} as twin plane and composition plane.  The strongest seven X-ray powder-diffraction lines [d in Å(I)(hkl)] are:

10.43 (42)(002)
3.573 (11)(025)
3.474 (100)(006)
3.186 (15)(224)
2.867 (13)(241)
2.606 (40)(008)
2.084 (15)(00·10)


     Electron-microscope analyses gave:

SiO2 - 27.32
Al2O3 - 0.03
MnO - 31.14

FeO - 1.12
MgO - 0.06
TiO2 - 9.44

Nb2O5 - 13.35
ZrO2 - 0.12
BaO - 8.88

K2O - 2.68
Na2O - 3.52
F - 0.84

H2O - 3.49
  (by TGA)
-O=F - 0.35


          Total 101.64%, corresponding to:


Na2.02K1.00Ba1.02(Mn7.73Fe0.27Mg0.03)(Ti2.08Nb1.77Zr0.02)


(Si8.01Al0.01)O32.00[(OH)5.62F0.78(H2O)0.60]S7.00.

TGA showed a two-stage weight loss with a break at 450° C.  The infrared-absorption spectrum confirms the presence of H2O and OH.  The name honors Professor Guy Perrault.

Keywords:  perraultite, new mineral species, silicate, Mont Saint-Hilaire, Quebec, occurrence, properties, X-ray data, chemical composition.


© 1991  The Canadian Mineralogist