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Articolo in rivista, 2014, ENG, 10.1180/minmag.2014.078.4.07

Ferri-fluoro-leakeite: a second occurrence at Bratthagen (Norway), with new data on Zn partitioning and the oxo component in sodium amphiboles

Oberti R.[1], Boiocchi M. [2], Hawthorne F.[3], Kristiansen R.[4]

[1] CNR-Istituto di Geoscienze e Georisorse, UOS Pavia, via Ferrata 1, I-27100 Pavia, Italy [2] Centro Grandi Strumenti, Universita` di Pavia, via Bassi 21, I-27100 Pavia, Italy [3] Department of Geological Sciences, University of Manitoba, Winnipeg, MB, R3T 2N2, Canada [4] PO Box 32, N-1650 Sellebakk, Norway

A second occurrence of ferri-fluoro-leakeite has been identified in the Bratthagen nepheline syenite pegmatite (Vestfold County, Norway). With respect to the holotype found at the Verkhnee Espe deposit (Akjailyautas Mountains, Kazakhstan; Ca´mara et al., 2010), it is closer to the ideal composition because of its larger Li and Mg contents and the absence of an oxo-component; however, it has a significant Zn content (0.29 a.p.f.u.). The ideal formula of ferri-fluoro-leakeite is ANaBNa2 C(Mg2Fe3+ 2 Li)TSi8O22 WF2 and the empirical formula derived from electron-microprobe analysis and single-crystal structure refinement for the sample used here is A(Na0.68K0.32)S=1.00 BNa2.00 C(Mg1.69Mn2+ 0.25Fe2+ 0.24Zn0.29Al0.23Fe3+1.50Ti0.02Li0.78)S=5.00 TSi8O22 W(F1.59(OH)0.41)S=2.00. Unitcell data are a = 9.788(2), b = 17.826(3), c = 5.282(1) A ? , b = 104.195(5)º, V = 893.5 (3) A ? 3, Z = 2. Crystal-chemical analysis shows that Li is ordered at the M(3) site and Zn is ordered mainly at the M(2) site, confirming previous findings for Li-bearing amphiboles. The new data also make quantification of the oxo component in Na amphiboles possible.

Mineralogical magazine (Print) 78 (4), pp. 861–869