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Progress in solving complex mineral structures from automated electron diffraction data: Charoite and Denisovite
No full textApplication of Automated Diffraction Tomography to structure solution of inorganic phases: Charoite
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Progress in solving complex mineral structures from automated electron diffraction data: Charoite and Denisovite
No full textThe structure of charoite, (K,Sr,Ba,Mn)(15-16)(Ca,Na)(32)[(Si-70(O,OH)(180))](OH,F)(4.0)center dot nH(2)O, solved by conventional and automated electron diffraction
No full textCharoite, ideally (K,Sr,Ba,Mn)(15-16)(Ca,Na)(32)[(Si-70(O,OH)(180))](OH,F)(4.0)center dot nH(2)O, a rare mineral from the Murun massif in Yakutiya, Russia, was studied using high-resolution transmission electron microscopy, selected-area electron diffraction, X-ray spectroscopy, precession electron diffraction and the newly developed technique of automated electron-diffraction tomography. The structure of charoite (a = 31.96(6) angstrom, b = 19.64(4) angstrom, c = 7.09(1) angstrom, beta = 90.0(1)degrees, V = 4450(24) angstrom(3), space group P2(1)/m) was solved ab initio by direct methods from 2878 unique observed reflections and refined to R-1/wR(2) = 0.17/0.21. The structure can be visualized as being composed of three different dreier silicate chains: a double dreier chain, [Si6O17](10-); a tubular loop-branched dreier triple chain, [Si12O30](12-); and a tubular hybrid dreier quadruple chain, [Si17O43](18-). The silicate chains occur between ribbons of edge-sharing Ca and Na-octahedra. The chains of tetrahedra and the ribbons of octahedra extend parallel to the z axis. K+, Ba2+, Sr2+, Mn2+ and H2O molecules lie inside tubes and channels of the structure. On the basis of microprobe analyses and occupancy refinement of the cation sites, the crystal chemical formula of this charoite can be written as (Z = 1): (K13.88Sr1.0Ba0.32Mn0.36)(Sigma 15.56)(Ca25.64Na6.36)Sigma 32 [(Si6O11(O,OH)(6))(2)(Si12O18(O,OH)(12))(2)(Si17O25(O,OH)(18))(2)](OH,F)(4.0)center dot 3.18H(2)O. RI Kolb, Ute/A-2642-2011; Mugnaioli, Enrico/E-6237-201
Charoite polytypes solved by Automated electron Diffraction Tomography (ADT) and Precession Electron Diffraction (PED)
No full textEssential features of the polytypic charoite-96 structure compared to charoite-90
No full textCharoite, ideally (K,Sr,Ba,Mn)(15-16)(Ca,Na)(32)[(Si(70)(O,OH)(180))](OH,F)(4)center dot nH(2)O, is a rock-forming mineral from the Murun massif in Yakutia, Sakha Republic, Siberia, Russia, where it occurs in a unique alkaline intrusion. Charoite occurs as four different polytypes, which are commonly intergrown in nanocrystalline fibres. We report the structure of charoite-96 (a = 32.11(6), b = 19.77(4), c = 7.23(1) angstrom, beta = 95.85(9)degrees, V = 4565(24) angstrom(3), space group P2(1)/m), which was solved ab initio by direct methods on the basis of 2676 unique electron diffraction reflections collected by automated diffraction tomography and refined to R(1)/wR(2) = 0.34/0.37. The structure of charoite-96 is related to that of the charoite-90, which was also solved recently. Both structures are composed of three different types of dreier silicate chains running along [001] and separated by ribbons of edge-sharing Ca- and Na-centred octahedra. In the structure of charoite-96, adjacent blocks formed by three different silicate chains and stacked along the x axis, are shifted by a translation of 1/2 e. The shifts involve a hybrid dreier quadruple chain, [Si(17)O(43)](18-) and a double dreier chain, [Si(6)O(17)](10-). In charoite-90 adjacent blocks are stacked without shifts. RI Mugnaioli, Enrico/E-6237-2011; Kolb, Ute/A-2642-201
Structure, polytypism and disorder of denisovite, K14Ca42Na6Si60O162F16(OH)4*2H2O, obtained by a combination of (S)TEM imaging, electron diffraction tomography and X-ray powder diffraction
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