Home > Mineral Abstracts > CanMin Vol. 25, pp. 763-766 (1987)




Vol. 25, pp. 763-766 (1987)



Poudretteite, KNa2B3Si12O30,
a new member of the osumilite group
from Mont Saint-Hilaire, Quebec,
and its crystal structure


Joel D. Grice, T. Scott Ercit and Jerry van Velthuizen
Mineral Sciences Division, National Museum of Natural Sciences,
Ottawa, Ontario K1A 0M8



Pete J. Dunn
Department of Mineral Sciences, Smithsonian Institution,
Washington, D.C. 20560, U.S.A.


ABSTRACT

          Poudretteite is a new mineral species from the Poudrette quarry, Mont St-Hilaire, Quebec.  It occurs in a marble xenolith included in a nepheline syenite, associated with pectolite, apophyllite, quartz and minor aegirine.  It forms clear, colorless to very pale pink, equidimensional, subhedral prisms up to 5 mm.  It is brittle, H about 5, with a splintery fracture; Dmeas. 2.51(1) g/cm3, dcalc. 2.53 g/cm3.  Uniaxial positive, w 1.516(1), e 1.532(1).  It is hexagonal, space group P6/mcc, a 10.239(1), c 13.485(3) Å and Z = 2.  The strongest ten X-ray diffraction lines in the powder pattern are:

6.74 (30)(002)
5.13 (100)(110)
4.07 (30)(112)
3.70 (30)(202)

3.369 (30)(004)
3.253 (100)(211)
2.956 (40)(300)
2.815 (60)(114)

2.686 (50)(213,204)
2.013 (30)(321)


     An analysis by electron-microprobe gave:

SiO2 - 77.7
B2O3 - 11.4
K2O - 5.2
Na2O - 6.2


     Sum 100.5 wt.%, which yields the empirical formula


K1.00(Na1.78K0.04)S1.91B3.05Si12.14O30.

     The structure, which is isotypic with that of osumilite, was refined to R = 3.0%, and is ordered with K in a [12]-coordinated C-site, Na in octahedrally coordinated A site, B in tetrahedrally coordinated T2 site, Si in tetrahedrally coordinated T1 site, and the B site is vacant.

Keywords:  poudretteite, new mineral species, osumilite group, Mont Saint-Hilaire, borosilicate, structure refinement.


© 1987  The Canadian Mineralogist