Home > Mineral Abstracts > CanMin Vol. 35, pp. 743-749 (1997)




Vol. 35, pp. 743-749 (1997)



Horváthite-(Y), rare-earth fluorocarbonate,
a new mineral species from
Mont Saint-Hilaire, Quebec


Joel D. Grice1
Research Division, Canadian Museum of Nature,
P.O. Box 3443, Station D, Ottawa , Ontario K1P 6P4



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


ABSTRACT

     Horváthite-(Y), ideally NaY(CO3)F2, is a new mineral species from Mont Saint-Hilaire, Quebec.  It occurs as tabular crystals up to 1 x 1 x 0.25 mm stacked in fan-shaped groups.  It is colorless to pale beige, with a white streak and a vitreous luster.  Associated minerals include microcline, aegirine, dawsonite, rhodochrosite, sodalite, natrolite, albite, sérandite, siderite, taeniolite, catapleiite, astrophyllite, genthelvite, and a franconite-group mineral.  It is soft (Mohs hardness ~4), brittle, with an uneven fracture and with very good {100} cleavage.  Horv├íthite-(Y) is biaxial negative, a 1.457 (1), b 1.543 (1), g 1.622 (1), 2Vmeas. = 82 (1)° and 2Vcalc. = 83°. It is orthorhombic, space group Pmcn, a 6.964 (3), b 9.173 (6), c 6.302 (2) Å3 and Z = 4.  The stongest eight X-ray powder-diffraction lines [d in Å (I)(hkl)] are:


5.19 (90)(011)
3.477 (100)(200)
2.800 (50)(130)
2.087 (50)(132,222)

2.057 (50)(141,013)
1.966 (50)(321)
1.849 (50)(330)
1.763 (50)(312,051)


     An average electron-microprobe analysis gave:


Na2O - 12.62
CaO - 1.86
Y2O3 - 45.07
Gd2O3 - 0.45

Dy2O3 - 2.49
Er2O3 - 3.02
Yb2O3 - 1.64
Ho2O3 - 0.81

Tb2O3 - 0.12
F - 17.22
CO2 - 19.83
O = F - 7.23


     Total 97.90 wt.%.  The proportion of CO2 was calculated by stoichiometry from the results of the crystal-structure analysis.  The empirical formula based on three atoms of oxygen is:


(Na0.90Ca0.07)S0.97 (Y0.89Gd0.01Dy0.03Er0.04Yb0.02Ho0.01)S1.00


(CO3)F2.01 or, ideally   NaY(CO3)F2.


     Dcalc. is equal to 3.613 g/cm3, and Dmeas. exceeds 3.3 g/cm3.  The structure has been refined to R = 1.6%.  The structure is layered perpendicular to [100], with a Na - Y - carbonate group layer and a layer of F atoms.  The structure of horvathite-(Y) seems unique among mineral structures, but ressembles that of synthetic BaCu(CO3)F2.

Keywords:  Horváthite-(Y), new mineral species, carbonate, crystal structure, Mont Saint-Hilaire, Quebec.

     1E-mail address:  jgrice@mus-nature.ca


© 1997  The Canadian Mineralogist