Abstract

The crystal structure of jinshajiangite from the Verkhnee Espe deposit, Kazakhstan, NaBaFe2+4Ti2(Si2O7)2O2(OH)2F, was refined from a twinned crystal to R1 = 3.13% on the basis of 6745 unique reflections [Fo > 4σFo], space group forumla, Z = 8, a 10.7059(5), b 13.7992(7), c 20.760(1) Å, α 90.008(1), β 94.972(1), γ 89.984(1)°, V 3055.4(4) Å3. The crystal used for the structure refinement was analyzed by electron microprobe. The empirical formula was calculated on 19 (O + F), with (OH + F) = 3 pfu: (Na0.77Ca0.23)Σ1(Ba0.60K0.36)Σ0.96(Fe2+2.33Fe3+0.26Mn1.26Zr0.04Mg0.02Zn0.01)Σ3.92(Ti1.79Nb0.18Mg0.02Al0.01)Σ4(Si2O7)2O3.93H1.93F1.07, Z = 8; Fe2O3 was calculated by analogy with jinshajiangite from Norra Karr, Sweden (Sokolova et al. 2009a) and H2O from the crystal-structure analysis. In the crystal structure, TS (Titanium Silicate) and I (Intermediate) blocks alternate along c. The TS block consists of HOH sheets (H-heteropolyhedral, O-octahedral). The topology of the TS block is as in Group II of the TS-block minerals where Ti (+ Nb) = 2 apfu. In the O sheet, ten [6]MO sites are occupied mainly by Fe2+, with <MO–φ> = 2.181 Å. In the H sheet, four [6]MH sites are occupied mainly by Ti, with <MH–φ> = 1.954 Å, and eight [4]Si sites are occupied by Si, with <Si–O> = 1.622 Å. The MH octahedra and Si2O7 groups constitute the H sheet. Fluorine atoms and OH groups are ordered at the XPM (H sheet) and XOA (O sheet) sites, respectively. The TS blocks link via common vertices of MH octahedra, i.e., MH–XPM– MH bridges. In the I block, Ba and K occur at the two AP sites, with Ba > K, and the two BP sites are occupied by Na and Ca, with Na > Ca. Jinshajiangite is isostructural with bobshannonite, Na2KBa(Nb,Ti)4Mn8(Si2O7)4O4(OH)4(O,F)2, Z = 4.

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