The 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.

Rozhdestvenskaya, I., Mugnaioli, E., Czank, M., Depmeier, W., Kolb, U., Reinholdt, A. and Weirich, T. (2010) The 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. Mineralogical Magazine, 74 (1). pp. 159-177. DOI 10.1180/minmag.2010.074.1.159.

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Abstract

Charoite, 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, [Si(6)O(17)](10-); a tubular loop-branched dreier triple chain, [Si(12)O(30)](12-); and a tubular hybrid dreier quadruple chain, [Si(17)O(43)](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(+), Ba(2+), Sr(2+), Mn(2+) and H(2)O 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): (K(13.88)Sr(1.0)Ba(0.32)Mn(0.36))(Sigma 15.56)(Ca(25.64)Na(6.36))Sigma 32 [(Si(6)O(11)(O,OH)(6))(2)(Si(12)O(18)(O,OH)(12))(2)(Si(17)O(25)(O,OH)(18 ))(2)](OH,F)(4.0)center dot 3.18H(2)O.

Document Type: Article
Keywords: charoite crystal structure analysis precession electron diffraction (PED) automated electron diffraction tomography (ADT) crystal-structure precession technique tomography
Research affiliation: Kiel University
DOI etc.: 10.1180/minmag.2010.074.1.159
ISSN: 0026-461X
Date Deposited: 22 Dec 2011 05:59
Last Modified: 23 Sep 2019 18:48
URI: http://oceanrep.geomar.de/id/eprint/15712

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