Crystal structure of titanium-rich eudialyte from the Kovdor Alkaline Massif

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Marco E. Ciriotti
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Crystal structure of titanium-rich eudialyte from the Kovdor Alkaline Massif

Messaggio da Marco E. Ciriotti » mer 08 ago, 2018 10:38

▪ Rastsvetaeva, R.K., Chukanov, N.V., Viktorova, K.A., Aksenov, S.M. (2018): New Data on Isomorphism in Eudialyte-Group Minerals. I. Crystal Structure of Titanium-Rich Eudialyte from the Kovdor Alkaline Massif. Crystallography Reports, 63, 563–569.

An abnormally titanium-rich mineral of the eudialyte group was studied by IR spectroscopy and X-ray diffraction. The trigonal unit cell parameters are a = 14.165(1) Å, c = 30.600(5) Å, V = 5317.23(4) Å3, sp. gr. R3m. The crystal structure was refined to R = 0.034 with anisotropic displacement parameters using 2530 reflections with F > 3σ(F). The idealized formula of the mineral (Z = 3) is Na8(H3O)5(K,Ce,Sr)2Ca6Zr2Ti1.2(Fe,Mn)0.6Si26O72(OH)2Cl·4H2O. At the ratio Zr: Ti ~ 2: 1, titanium atoms lie in four sites and are not predominant in any of them. Another distinguishing feature of the mineral is the structural separation of chemical elements, such that K, Sr, and Ce cations and H3O groups are randomly distributed between four split sites to form polyhedra with different volumes. The isomorphism of Zr and Ti in eudialyte-group minerals is discussed.

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Marco E. Ciriotti

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