The crystal structure of natural Fe-rich chevkinite-(Ce)

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 Fe-rich chevkinite(Ce) ranges from 10.97 % to 11.59 % (wt.) and Ce 2 O 3 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 C 2/ m ( R = 2.41 %). Cell parameters are a = 13.456(3) A, b = 5.728(1) A, c = 11.083(2) A, β = 100.60(3)°, V = 839.7(3) A 3 , Z = 2. The structure of Fe-rich chevkinite-(Ce) is made up of two kinds of sheets, one is a sheet of Si 2 O 7 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 1-polyhedra and 10-coordinated A 2-polyhedra. The Fe and Ti are partially ordered among the octahedral sites of B , C 1, C 2A and C 2B. The Charge Distribution analysis confirms Fe 3+ /ΣFe = 0.61 and a mixture of Fe 2+ and Fe 3+ in the B site. The chemical formula for the natural Fe-rich chevkinite-(Ce) is (Ce 3+ 1.76 La 0.89 Ca 0.46 Nd 0.22 Pr 0.18 Sm 0.04 Gd 0.04 Th 0.03 Ba 0.01 □ 0.37 )Σ 4.00 (Fe 3+ 0.29 Ti 0.21 Fe 2+ 0.18 Mn 2+ 0.13 Mg 0.18 □ 0.11 ) Σ1.00 (Ti 2.16 Fe 3+ 0.81 Fe 2+ 0.52 Nb 0.16 Al 0.06 □ 0.08 ) Σ4.00 Si 4 O 20.72 (OH) 1.28. .