Quick Search:    advanced search

GSW Home   GeoRef Home   My GSW Alerts   Contact GSW   About GSW   Journals List   Help

This Article Résumé Figures Only Full Text Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in ISI Web of Science Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Grice, J. D. Articles by Wight, Q. Search for Related Content GeoRef GeoRef Citation

TUNDRITE-(Ce) FROM MONT SAINT-HILAIRE, QUEBEC: CRYSTAL-STRUCTURE ANALYSIS AND SPECIES CHARACTERIZATION

Joel D. Grice^1,, Ralph Rowe¹, Glenn Poirier¹ and Quintin Wight²

¹ Research Division, Canadian Museum of Nature, P.O. Box 3443, Station D, Ottawa, Ontario K1P 6P4, Canada
² 525 Fielding Drive, Ottawa, Ontario K1V 7G7, Canada

E-mail address: jgrice{at}mus-nature.ca

Tundrite-(Ce), ideally Na₂Ce₂TiO₂(SiO₄)(CO₃)₂, has been found recently in the Mont Saint-Hilaire quarry, Quebec. It occurs as yellow-green, bladed, singly terminated crystals up to 9 mm in length. Minerals associated with tundrite-(Ce) are aegirine, analcime, an astrophyllite-group mineral, catapleiite, a eudialyte-group mineral, gonnardite, mangan-neptunite, monazite-(Ce), natrolite, rhodochrosite, sphalerite and vinogradovite. Tundrite-(Ce) is triclinic, space group P, with the following unit-cell parameters, refined from powder-diffraction data: a 7.5702(6), b 13.949(2), c 5.0235(5) Å, 100.19(1), β 70.88(1), 101.26(1)°, V 487.91(6) ų and Z = 2. Crystals are tabular on {010} and elongate on [001], with pinacoid forms: {100}, {010}, {201} and {01}. Electron-microprobe analyses give the average and ranges: Na₂O 9.44 (9.07–9.66), CaO 0.34 (0.16–0.42), La₂O₃ 16.12 (15.26–17.95), Ce₂O₃ 27.01 (25.41–28.56), Pr₂O₃ 2.13 (1.72–2.38), Nd₂O₃ 6.16 (5.61–6.58), Sm₂O₃(0.38 (0.18–0.73), TiO₂ 11.17 (10.73–11.93), Nb₂O₅ 2.30 (1.14–3.11), Ta₂O₅ 0.07 (0.00–0.15), SiO₂ 9.32 (9.10–9.54), CO₂ 13.91 (TGA), H₂O 0.36 (TGA), for a total of 98.80 (97.43–100.17) wt.%. The empirical formula based on the crystal-structure analysis, ideally showing 24 oxygen atoms, is 2[(Na_1.906Ca_0.039) _1.945 (Ce_1.030La_0.621Nd_0.229Pr_0.081Sm_0.014) _1.975 (Ti_0.875Nb_0.109) _0.984O₂H_0.250 (Si_0.971O₄)(C_0.989O₃)₂]. The structure has been refined to an R index of 2.7% for 2827 unique reflections. The structure has three chemically distinct layers parallel to (010): (1) a Na–Ti–Si–O slab, (2) a Ce–C–O slab and (3) a Na–O slab. Slabs are cross-linked by independent [CO₃]^2– and [SiO₄]^4– groups. Minor amounts of OH are present to ensure charge balance as a result of the substitutions Nb Ti and Ca REE.

Keywords: tundrite-(Ce), crystal structure, rare-earth elements, chemical composition, infrared spectroscopy, hydrogen, Mont Saint-Hilaire, Quebec.