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 Citation Map 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 Tait, K. T. Articles by Galliski, M. A. Search for Related Content GeoRef GeoRef Citation

BOBFERGUSONITE FROM THE NANCY PEGMATITE, SAN LUIS RANGE, ARGENTINA: CRYSTAL-STRUCTURE REFINEMENT AND CHEMICAL COMPOSITION

Kimberly T. Tait¹, Frank C. Hawthorne^1,, Petr ern¹ and Miguel A. Galliski²

¹ Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba R3T 2N2, Canada
² IANIGLA, CRICYT (CONICET), Avda A. Ruiz Leal s/n Parque Gral. San Martín, CC330, 5500 Mendoza, Argentina

E-mail address: frank_hawthorne{at}umanitoba.ca

A second occurrence of bobfergusonite, ideally Na₂ Mn₅ ²⁺ Fe³⁺ Al (PO₄)₆, has been discovered at the Nancy pegmatite, San Luis Range, Argentina. The Nancy pegmatite is a small, poorly evolved pegmatite of the beryl–columbite–phosphate subtype of rare-element pegmatites. Bobfergusonite from the Nancy pegmatite is monoclinic, a 12.796(3), b 12.465(2), c 11.001(2) Å, ß 97.39(3)°, V 1740.1(5) ų, P2₁/n, Z = 4, has been refined to an R-index of 2.6% for 2959 observed (|F_o| 4F) reflections measured with MoK X-radiation on a Bruker P4 diffractometer equipped with a CCD detector. The crystal used for the collection of the X-ray intensity data was subsequently analyzed with an electron microprobe. The unit formula derived from the refined site-scattering values and electron-microprobe results is (Na_{1.10 0.90}) (Na_{0.90 0.10}) Mn²⁺ (Mn_0.89 ²⁺ Ca_0.11) (Fe_0.91 ²⁺ Fe_0.49 ³⁺ Mn_0.32 ²⁺ Mg_0.28) (Fe_0.42 ³⁺ Fe_0.28 ²⁺ Mg_0.30) (Al_0.94 Fe_0.06 ³⁺) (PO₄)₆. In bobfergusonite, there are six M sites, each coordinated by six O-atoms in an octahedral arrangement with <M–O> distances ranging from 1.918 Å at M(6) to 2.237 Å at M(2). There is strong order between the divalent and trivalent cations over the six M sites, and there is also strong order between Al and Fe³⁺. There are five X sites, X(1)–X(5), each having a wide dispersion of X–O distances. The X(1) site is mainly occupied by Mn²⁺ and has octahedral coordination. The X(2) and X(3) sites are each [8]-coordinated, the X(4) and X(5) sites are [7]-coordinated, and X(2)–X(5) are all approximately half-occupied by Na. In all of the alluaudite-related structures, the M sites form linear edge-sharing trimers, and the alluaudite, wyllieite and bobfergusonite structures show subtly different patterns of cation order–disorder. Bobfergusonite crystals from both known localities, the Nancy pegmatite (Argentina) and the Cross Lake pegmatite (Manitoba), are considerably disordered.

Keywords: bobfergusonite, crystal structure, phosphate, Argentina.

This article has been cited by other articles:

				P. Cerny and T. S. Ercit THE CLASSIFICATION OF GRANITIC PEGMATITES REVISITED Can Mineral, December 1, 2005; 43(6): 2005 - 2026. [Abstract] [Full Text] [PDF]