Poudretteite, KNaSi1230 – Saint-Hilaire

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

Poudretteite, KNaSi₁₂₃₀
a new member of the osumilite group
from Mont Saint-Hilaire, Quebec,
and its crystal structure

Joel D. Grice, T. Scott ErcitandJerry 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; D_meas. 2.51(1) g/cm, d_calc. 2.53 g/cm. Uniaxial positive, 1.516(1), 1.532(1). It is hexagonal, space group 6/mcc, 10.239(1), 13.485(3) Å and = 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

K_1.00(Na_1.78K_0.04)_S1.91B_3.05Si_12.14O₃₀.

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 Asite, B in tetrahedrally coordinated T2 site, Si in tetrahedrally coordinated T1 site, and the B site is vacant.