The crystal structure of natural Fe-rich chevkinite-(Ce)
Yang, Z., Fleck, M., Smith, M.P., Tao, K., Song, R. and Zhang, P. (2002) The crystal structure of natural Fe-rich chevkinite-(Ce) European Journal of Mineralogy, 14 (5). pp. 969-975. ISSN 0935-1221
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Chemical composition and crystal structure of natural non-metamict Fe-rich chevkinite-(Ce) from the aegirine-alkali granite, Mianning, Sichuan Province, China, were investigated. Microprobe analyses indicated that FeO (total iron) content in Ferich chevkinite(Ce) ranges from 10.97 % to 11.59 % (wt.) and Ce2O3 from 23 % to 25 %. There are deficient A- and (B + C)-type cations in the formula. The crystal structure of Fe-rich chevkinite-(Ce) was refined from CCD data in the space-group type C2/m (R = 2.41 %). Cell parameters are a= 13.456(3) Ã…, b = 5.728(1) Ã…, c = 11.083(2) Ã…, Î² = 100.60(3)Â°, V = 839.7(3) Ã…3, Z = 2. The structure of Fe-rich chevkinite-(Ce) is made up of two kinds of sheets, one is a sheet of Si2O7 groups and B-octahedra, and the other is a sheet of C-octahedra, both parallel to the ab plane.The two kinds of sheets alternate along c axis and form a three dimensional framework. The rare earth ions lie between the disilicate groups and the sheets of octahedra to form (8+3)-coordinated A-polyhedra and 10-coordinated A2-polyhedra. The Fe and Ti are partially ordered among the octahedral sites of B, C1, C2A and C2B. The Charge Distribution analysis confirms Fe3+/Î£Fe = 0.61 and a mixture of Fe2+ and Fe3+ in the B site. The chemical formula for the natural Fe-rich chevkinite-(Ce) is (Ce3+1.76La0.89Ca0.46Nd0.22Pr0.18Sm0.04Gd0.04Th0.03Ba0.01 □0.37)Î£4.00(Fe3+0.29Ti0.21Fe2+0.18Mn2+0.13Mg0.08□0.11)Ïƒ1.00(Ti2.16Fe3+0.81F2+0.52Nb0.16Al0.06□0.08)Î£4.00 Si4O20.72(OH)1.28.
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