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

Abstract

AbstractA 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; Cámaraet 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 isANaBNa2C(Mg2Fe23+Li)TSi8O22WF2and the empirical formula derived from electron-microprobe analysis and single-crystal structure refinement for the sample used here isA(Na0.68K0.32)S=1.00BNa2.00C(Mg1.69Mn0.252+Fe0.242+Zn0.29Al0.23Fe1.503+Ti0.02Li0.78)S=5.00TSi8O22W(F1.59(OH)0.41)S=2.00. Unitcell data area= 9.788(2),b= 17.826(3),c= 5.282(1) Å, β = 104.195(5)°,V= 893.5 (3) Å3,Z= 2. Crystal-chemical analysis shows that Li is ordered at theM(3) site and Zn is ordered mainly at theM(2) site, confirming previous findings for Li-bearing amphiboles. The new data also make quantification of the oxo component in Na amphiboles possible.