Journal of the Mineralogical Society of America
Vol. 82, pp. 1255-1260 (1997)

Lukechangite-(Ce), a new rare-earth-fluorocarbonate mineral
from Mont Saint-Hilaire, Quebec
Joel D. Grice¹ and G. Y. Chao^2
1Research Division, Canadian Museum of Nature, P.O. Box 3443,
Station D, Ottawa, Ontario, Canada  K1P 6P4
²Ottawa-Carleton Geoscience Centre, Department of Earth Sciences,
Carleton University, Ottawa, Ontario, Canada  K1S 5B6

ABSTRACT

     Lukechangite-(Ce), ideally Na₃Ce₂(CO₃)₄F, is a new mineral from Mont Saint-Hilaire, Quebec.  It occurs as tabular, short prismatic, and barrel-shaped crystals up to 1mm.  It is colorless to pale beige with a white streak and a vitreous, or somewhat pearly on {0001}, luster.  Associated minerals include microcline, analcime, sodalite, aegirine, serandite, eudialyte, catapleiite, fluorite, petersenite-(Ce), siderite, astrophyllite, and albite.  Lukechangite-(Ce) is soft, Mohs hardness ~ 4½, brittle, with an uneven to conchoidal fracture, and with perfect {0001} cleavage.  Lukechangite-(Ce) is uniaxial negative w  = 1.728 (3) and e = 1.542 (1).  It is hexagonal, space group P6₃/mmc, a = 5.068 (1), c + 22.87 (5) Å, V = 509 (1) ų, and Z = 2.  The strongest X-ray powder diffraction lines [d (Å), I, hkl] are:

     An average of the electron-microprobe analyses gave:

     Total 99.30 wt%.  CO₂ was calculated by stoichiometry from the results of the crystal-structure analysis.  D_calc is 4.02 g/cm³.   The atomic arrangement of lukechangite-(Ce) has been refined to R = 3.4%.  The structure is layered parallel to {001}, with CO₃ groups oriented parallel to the layering forming thick slabs incorporating either Ce or Na cations and a separate Na-F layer.   The structure of lukechangite-(Ce) resembles that of huanghoite-(Ce) and baiyuneboite-(Ce) and is isostructural with synthetic Na₃La₂(CO₃)₄F.

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