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Journal Wuhan University of Technology
9(3), 9-14 (1994)

A new mineral - Fluorbritholite-(Ce)

Jiexiang Gu, G.Y. Chao and Suren Tang
Journal Wuhan University of Technology, 9(3), 9-14 (1994)

ABSTRACT

     The mineral is present in vugs in nepheline syenite, marble xenoliths, sodalite syenite xenoliths, and pegmatite dikes at Mont Saint-Hilaire, Quebec.  Occurs as pale yellow, tan, or reddish-brown aggregates and patches consisting of radiating to subparallel groups in which crystals are prismatic (to 0.5mm) to nearly equant.  Colorless to pale brown streak, adamantine luster, opaque to translucent, brittle, even to conchoidal fracture, perfect {0001} cleavage, H = 5, nonfluorescent, Dmeas = 4.66 (1), Dcalc = 4.66 g/cm3 for Z = 2.  Pale yellow in transmitted light, nonpleochroic, uniaxial negative, w 1.792 (5), e 1.785 (5).  Electron microprobe analyses of three grains gave:


Ce2O3 29.17, 28.70, 33.14
La2O3 15.80, 20.21, 19.78
Pr2O3 3.52, 1.69, 1.20

Nd2O3 8.83, 4.62, 8.78
Sm2O3 0.67, 0.25, -
FeO -, -, 0.10

CaO 13.96, 12.87, 1.92
SrO 0.45, 1.18, 3.74
MgO 0.02, -, -

MnO -, 1.39, 1.48
Na2O 0.01, 0.85, 3.04
ThO2 1.74, 1.84, 1.09

U3O8 0.30, 0.11, 0.31
SiO2 20.61, 16.92, 16.59
Al2O3 -, -, 0.08

P2O5 2.84, 7.25, 5.21
F 2.38, 2.58, 2.70
F = O 1.00, 1.09, 1.14


     Sum 100.56, 99.73, 99.20 wt%; these correspond to, respectively:


(Ca1.95Ce1.39La0.76Nd0.31Pr0.17Y0.09Th0.05Sr0.03Sm0.03)S4.78(Si2.68P0.31)S2.99O12.02F0.98


(Ca1.77Ce1.35La0.96Nd0.21Na0.21Mn0.15Sr0.09Pr0.08Th0.05Y0.02Sm0.01)S4.90(Sr2.17P0.79)S2.96O11.95F1.05


(Ce1.69La1.02Na0.82Nd0.44Sr0.30Ca0.29Mn0.17Y0.09Th0.03Fe0.01)S4.92(Si2.32P0.61)S2.93O11.81-F1.19


     Single-crystal X-ray study indicated hexagonal symmetry, space group P63/m; for the above composition, a = 9.537 (5), 9.517 (5), 9.537 (6), c = 6.999 (4) Å.  Strongest lines of the powder pattern (114mm Gandolfi, CuKa radiation) are:


2.845 (100,211)
2.822 (40,112)
1.970 (30,222)
1.870 (40,213)


     and  (corresponding to the first analysis, after heating the sample to 800°C for 3 h); for the third composition (unheated sample):


2.840 (100)
2.818 (30)
2.748 (30)
1.868 (30)


     Type material is in the Canadian Museum of Nature, Ottawa.   The mineral has been described previously from other localities, and the new name has been introduced to distinguish the F-rich and OH-rich members, analogous to that for the apatite and apophyllite groups.  The authors suggest that britholite-(Ce) and britholite-(Y) be renamed hydroxylbritholite-(Ce) and hydroxylbritholite-(Y).  The authors also recognize that in the Mont Saint-Hilaire material the third composition given above is Ca-rich, but no distinction is made because the structural significance of the Ca contents is not known.


© 1994  Journal Wuhan University of Technology