Quick Search:    advanced search

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

This Article 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 Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via HighWire Citing Articles via Google Scholar Google Scholar Articles by BRIGATTI, M. F. Articles by POPPI, L. Search for Related Content GeoRef GeoRef Citation

Crystal chemistry of apatites from the Tapira carbonatite complex, Brazil

¹ Dipartimento di Scienze della Terra dell'Università di Modena e Reggio Emilia, Via S. Eufemia 19, I-41100 Modena, Italy
² CNR - Istituto di Metodologie per l'Analisi Ambientale, C.da S. Loja, I-85050 Tito Scalo (PZ), Italy
³ CNR - Istituto di Geoscienze e Georisorse, Sezione di Pavia, Via Ferrata 1, I-27100 Pavia, Italy

^* E-mail: brigatti{at}unimo.it

The crystal chemistry of ten hydroxyl fluorapatite crystals from the Tapira alkaline carbonatitic complex (Brazil) was investigated by electron microprobe, ion microprobe, infrared spectroscopy and single crystal X-ray diffraction. Apatite crystals are characterized by modest REE and a very low Cl content. They exhibit the following compositional range in atoms per formula unit 9.935 Ca 10.024, 5.926 P 6.006, 0.005 REE 0.046, 0.422 F 0.914, 0.003 Cl 0.008, 0.003 Si 0.038; Na is present in trace.

Crystal structure refinements were carried out in space group P6₃/m, (R values varies between 0.016 and 0.028). The REE for Ca substitution requires two different exchange mechanisms producing an increase in the bond valence on the X anionic site: the deprotonation of OH and/or the substitution of CO^2-₃ for OH. The CO^2-₃ substitution in the anionic sites of investigated structures was related to great CO₂ activity of the melt whereas deprotonation of the apatite crystals could be related to the highly oxidizing nature of the Tapira carbonatitic magma. The very low Cl/F ratio suggests that the crystallization of Tapira pluton was relatively shallow. The determination of REE partitioning between the Ca1 and Ca2 sites is difficult because of the low REE content. A proportional increase in the size of the Ca1 and Ca2 sites was observed with increasing REE content as well as an overall increase of a parameter.

Key-words: apatite, crystal structure, chemistry, carbonatite, rare earth elements.

This article has been cited by other articles:

				R. C. Tacker Carbonate in igneous and metamorphic fluorapatite: Two type A and two type B substitutions American Mineralogist, January 1, 2008; 93(1): 168 - 176. [Abstract] [Full Text] [PDF]

				A. R. CHAKHMOURADIAN and L. MEDICI Clinohydroxylapatite: a new apatite-group mineral from northwestern Ontario (Canada), and new data on the extent of Na-S substitution in natural apatites European Journal of Mineralogy, February 1, 2006; 18(1): 105 - 112. [Abstract] [Full Text] [PDF]