The structure of charoite, (K,Sr,Ba,Mn) (sub 15-16) (Ca, Na) (sub 32) [(Si (sub 70) (O,OH) (sub 180) )](OH,F) (sub 40) .nH (sub 2) O, solved by conventional and automated electron diffraction
The structure of charoite, (K,Sr,Ba,Mn) (sub 15-16) (Ca, Na) (sub 32) [(Si (sub 70) (O,OH) (sub 180) )](OH,F) (sub 40) .nH (sub 2) O, solved by conventional and automated electron diffraction
Mineralogical Magazine (February 2010) 74 (1): 159-177
- Asia
- cell dimensions
- chain silicates
- charoite
- Commonwealth of Independent States
- computed tomography
- crystal chemistry
- crystal structure
- electron diffraction data
- formula
- high-resolution methods
- lattice parameters
- polyhedra
- Russian Federation
- Siberia
- silicates
- TEM data
- tomography
- X-ray diffraction data
- Yakutia Russian Federation
- Murun Massif
Charoite, ideally (K,Sr,Ba,Mn) (sub 15-16) (Ca,Na) (sub 32) [(Si (sub 70) (O,OH) (sub 180) )] (OH,F) (sub 4.0) .nH (sub 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) Aa, b=19.64(4) Aa, c=7.09(1) Aa, beta =90.0(1) degrees , V=4450(24) Aa (super 3) , space group P2 (sub 1) /m) was solved ab initio by direct methods from 2878 unique observed reflections and refined to R (sub 1) /wR (sub 2) =0.17/0.21. The structure can be visualized as being composed of three different dreier silicate chains: a double dreier chain, [Si (sub 6) O (sub 17) ] (super 10-) ; a tubular loop-branched dreier triple chain, [Si (sub 12) O (sub 30) ] (super 12-) ; and a tubular hybrid dreier quadruple chain, [Si (sub 17) O (sub 43) ] (super 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 (super +) , Ba (super 2+) , Sr (super 2+) , Mn (super 2+) and H (sub 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 (sub 13.88) Sr (sub 1.0) Ba (sub 0.32) Mn (sub 0.36) ) (sub Sigma 15.56) (Ca (sub 25.64) Na (sub 6.36) ) (sub Sigma 32) [(Si (sub 6) O (sub 11) (O,OH) (sub 6) ) (sub 2) (Si (sub 12) O (sub 18) (O,OH) (sub 12) ) (sub 2) (Si (sub 17) O (sub 25) (O,OH) (sub 18) ) (sub 2) ](OH,F) (sub 4.0) .3.18H (sub 2) O.
