Home > Mineral Abstracts > CanMin Vol. 32, pp. 405-414 (1994)




Vol. 32, pp. 405-414 (1994)



Petersenite-(Ce), a new mineral
from Mont St-Hilaire,
and its structural relationship
to other REE carbonates


Joel D. Grice, Jerry Van Velthuizen and Robert A. Gault
Mineral Sciences Section, Canadian Museum of Nature,
Ottawa, Ontario K1P 6P4


ABSTRACT

          Petersenite-(Ce) is a newly discovered rare-earth-element carbonate from the Poudrette quarry, Mont St-Hilaire, Quebec.  It is grey, with a slight pink tint, forming striated prisms up to 7mm in length.  It has a vitreous luster and is translucent to transparent.  Petersenite-(Ce) is relatively soft (Mohs hardness ~3) and very brittle, having a conchoidal fracture.  Optical properties are biaxial, with moderate dispersion, no absorption, and indices of refraction a 1.623(1), b 1.636(10, g 1.649(1), 2Vmeas. = 89.7(5)° and 2Vcalc. = 89.8°, and an optical orientation of X = b, Y & c = 30° and Z = a.  Electron-microprobe analyses gave:

Na2O 17.38
CaO - 1.32
BaO - 0.32
SrO - 1.70

La2O3 - 14.49
Ce2O3 - 23.66
Pr2O3 - 2.00
Nd2O3 - 5.82

Sm2O3 - 0.60
CO2 - 32.92


          CO2 (from crystal-structure analysis) , total 100.21 wt.%, which yields the empirical formula


(Na3.75Ca0.16)(Ce0.96La0.59Nd0.23Sr0.11Pr0.08Sm0.02Ba0.01)(CO3)5 or,


ideally, Na4(REE)2(CO3)5 for Z = 4,


with Dcalc. = 3.67 g/cm3  and Dmeas. = 3.69 g/cm3.   Crystal-structure analysis shows the mineral to be monoclinic, space group P21, with a 20.872(4), b 6.367(1), c 10.601(2) Å and b 120.50(3)°.  The strongest lines in the X-ray powder pattern [d Å (I)(hkl)] are:

9.13 (3)(201, 001)
5.22 (5)(211, 011,
  201, 401)
4.13 (3)(501,301)
3.70 (4)(412, 012)


2.607 (10)(402, 802,
  420)
2.148 (3)(814, 014)
1.921 (3)(432, 032,
  430)

     The crystal structure has the subcell of burbankite and remondite-(Ce), but the supercell changes the ratio of [8]-coordinated to [10]-coordinated cations.  The layered structure is compared to that of other REE carbonates.

Keywords:  Petersenite-(Ce), new mineral species, rare-earth element, carbonate, crystal structure, Mont St-Hilaire, Quebec.


© 1994  The Canadian Mineralogist