Home > Mineral Abstracts > CanMin Vol. 35, pp. 1035-1039 (1997)




Vol. 35, pp. 1035-1039 (1997)



Normandite, the Ti-analogue of låvenite
from Mont Saint-Hilaire, Quebec


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



Robert A. Gault**
Research Division, Canadian Museum of Nature,
Ottawa , Ontario K1P 6P4


ABSTRACT

     Normandite, the titanium analogue of låvenite, is a new mineral species from the Poudrette quarry, Mont Saint-Hilaire, Quebec.  It is found in nepheline syenite and in miarolitic cavities in nepheline syenite, associated with nepheline, albite, microcline, aegirine, natrolite, catapleiite, kupletskite, eudialyte, cancrinite, villiaumite, rinkite, and donnayite-(Y).
It occurs as transparent to translucent orange-brown aggregates of subparallel acicular crystals up to 10 mm in length, and as patches of yellow, fibrous crystals.  It has a white to very pale yellow streak and vitreous luster.  It is brittle, with distinct {100} and {001} cleavages, and a conchoidal fracture.  Normandite is biaxial negative, with indices of refraction a 1.743 (2), b 1.785 (2), and  g 1.810 (5), 2V meas. in the range 72-84°, 2V calc. = 74° and a moderate dispersion r  > v.  Pleochroism is pronounced:  X pale yellow, Y yellow, Z brownish red to deep red.  The optical orientation is Y = b, X ^ c = 15° (in obtuse angle b).  Normandite is monoclinic, space group P21/a, with a 10.828 (7), b 9.790 (7), c 7.054 (2) Å, b 108.20 (3)°, V 709.9 (8) Å3 and Z = 4.  The strongest six lines of the
X-ray powder-diffraction pattern [d in Å (I)(hkl)] are:


3.942 (20)(121)
3.234 (30)(310)
2.859 (100)(122)

2.807 (70)(320)
1.762 (20)(204)
1.741 (20)(242)


      The crystals are elongate on {001} and flattened on {010}, with the following forms, in order of predominance:  {100}, {110} and {001}.  Electron-microprobe analyses gave:


Na2O - 9.26
(9.10-9.40)
K2O - 0.01
(0.01-0.02)
CaO - 15.38
(15.08-15.59)
MnO - 9.31
(9.11-9.52)


FeO - 6.13
(5.89-6.26)
TiO2 - 17.51
(17.09-17.83)
Nb2O5 - 3.89
(3.51-4.61)
ZrO2 - 2.62
(2.29-2.73)


SiO2 - 31.92
(31.69-32.04)
F - 5.11
(4.82-5.31)
O = F - -2.15
Total 98.99 wt.%.




     The empirical formula based on 9(O + F) is:


Na1.12Ca1.03(Mn0.49Fe0.32)S0.81 (Ti0.82Nb0.11Zr0.08)S1.01


Si2.00O7.99F1.01, ideally NaCa(Mn,Fe)(Ti,Nb,Zr)Si2O7OF.


     D meas. = 3.50 (1), Dcalc. = 3.48 g/cm3.  The name honors Charles Normand, who discovered the species.

Keywords:  normandite, new mineral species, Ti-analogue of låvenite, Mont Saint-Hilaire, Quebec.

     * Present address:  2031 Delmar Drive, Ottawa, Ontario  K1H 5P6
     **  E-mail address: rgault@mus-nature.ca


© 1997  The Canadian Mineralogist