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Jinshajiangite: structure, twinning and pseudo-symmetry TEXT SIZE: A A A
The crystal structure of jinshajiangite based on a sample from its original discovery location is studied using single-crystal X-ray diffraction and transmission electron microscopy methods. Jinshajiangite is a titanium silicate mineral with an ideal chemical formula of BaNaFe4Ti2(Si2O7)( 2)O-2 (OH) 2 F. The structure of jinshajiangite is of P (1) over bar symmetry (triclinic system), with a = 8.7331 (2) angstrom, b = 8.7366 (2) angstrom, c = 11.0404 (3) angstrom, alpha = 81.477 (1)degrees, beta = 110.184 (1)degrees, gamma = 104.384 (1)degrees and V = 764.03 (3) angstrom(3), instead of the previously proposed C (1) over bar cell [a = 10.7059 (5) angstrom, b = 13.7992 (7) angstrom, c = 20.760 (1) angstrom, alpha = 90.008 (1)degrees, beta = 94.972 (1)degrees, gamma = 89.984 (1)degrees, V = 3055.4 (4)angstrom(3)]. The basic topology of the new structure is similar to the previously proposed C (1) over bar structure, except there is only one type of titanium silicate and intermediate cation layer in the structure (instead of two types), which are all related by the translation along the c-axis. Even though there is a significant amount of Mn in the chemical composition, no obvious ordering between Fe and Mn is observed in the structure. All the mineral species of the perraultite-type structure (jinshajiangite, perraultite, surkhobite and bobshannonite) should have the same P (1) over bar structure as jinshajiangite with similar to 10 angstrom d(001) spacing, and all the previously proposed monoclinic space groups were pseudosymmetry generated by nanoscale polysynthetic twinning on the (001) composition plane. The similar phenomenon observed in bafertisite is also discussed in the paper with an alternative polytype structure model proposed.
 

Publication name

 ACTA CRYSTALLOGRAPHICA SECTION B-STRUCTURAL SCIENCE CRYSTAL ENGINEERING AND MATERIALS, 74 325-336; 10.1107/S2052520618006753 4 AUG 2018

Author(s)

 Jin, Shiyun; Xu, Huifang; Lee, Seungyeol; Fu, Pingqiu

Corresponding author(s) 

 XU Huifang 
 hfxu@geology.wisc.edu  
 Univ Wisconsin, Dept Geosci, 1215 W Dayton St, Madison, WI 53706 USA
 Chinese Acad Sci, Inst Geochem Guiyang, Guiyang, Guizhou, Peoples R China

Author(s) from IGCAS   FU Pingqiu

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