• journal_title：Mineralogical Magazine
• Contributor：E. Sokolova ; F. C. Hawthorne ; L. A. Pautov ; A. A. Agakhanov ; V. Yu. Karpenko
• Publisher：Mineralogical Society of Great Britain and Ireland
• Date：2011-
• Format：text/html
• Language：en
• Identifier：10.1180/minmag.2011.075.5.2583
• journal_abbrev：Mineralogical Magazine
• issn：0026-461X
• volume：75
• issue：5
• firstpage：2583
• section：Articles

The crystal structure of mendeleevite-(Ce), (Cs,□)₆(□,Cs)₆(□,K)₆(REE,Ca,□)₃₀(Si₇₀O₁₇₅) (H₂O,OH,F,□)₃₅, a new mineral from the moraine of the Darai-Pioz glacier, the Alai mountain ridge, Tien-Shan mountains, northern Tajikistan, was solved by direct methods and refined to R₁ = 4.15% based on 2274 observed [F_o > 4σ|F|] unique reflections measured with Mo-Kα radiation on a Bruker P4 diffractometer equipped with a CCD detector. Mendeleevite-(Ce) is cubic, space group Pm, a 21.9148(4) Å, V 10525(1) ų, Z = 2, D_calc = 3.066 g/cm³. The empirical formula (electron microprobe) is Cs_5.94 K_2.22 [(Ce_11.35La_5.86Nd_3.23 Pr_1.54 Sm_0.32Gd_0.20)_Σ22.50(Ca_4.68Sr_1.00)_Σ5.68]_Σ28.18Si_70.12O_203.17H_45.67F_6.83, Z = 2, calculated on the basis of 210 (O + F) a.p.f.u., with H₂O and OH calculated from structure refinement (OH + F = 17 p.f.u.; H₂O = 17.75 p.f.u.).

The structural formula is (Cs_4.65□_1.35)_Σ6(□_4.71Cs_1.29)_Σ6(□_3.78K_2.22)_Σ6{[(Ce_11.35La_5.86Nd_3.23 Pr_1.54Sm_0.32Gd_0.20)_Σ22.50(Ca_4.68Sr_1.00)_Σ5.68]_Σ28.18□_1.82}_Σ30(Si₇₀O₁₇₅)[(OH)_10.17F_6.83]_Σ17(H₂O)_17.75. Simplified and endmember formulae are as follows: (Cs,□)₆(□,Cs)₆(□,K)₆(REE,Ca,□)₃₀(Si₇₀O₁₇₅) (H₂O,OH,F,□)₃₅ and Cs₆(REE₂₂Ca₆)(Si₇₀O₁₇₅)(OH,F)₁₄(H₂O)₂₁. The crystal structure of mendeleevite-(Ce) is an intercalation of two independent Si–O radicals and an M framework of (REE,Ca) polyhedra. The Si–O radicals are an (Si₁₀₄O₂₆₀)¹⁰⁴⁻ framework and an (Si₃₆O₉₀)³⁶⁻cluster which do not link directly. The M framework is located between the Si–O framework and the Si–O clusters. Interstitial cations occupy two types of cages and channels. Cages I and II are 78 and 22% occupied by Cs. Channels along [100] contain K atoms and H₂O groups. Mendeleevite-(Ce) has no natural or synthetic structural analogues. Mendeleevite-(Ce) is a framework mineral with large cavities and it has the potential to be used as a model for the synthesis of microporous materials of industrial interest.