Modular structure of highly ordered hydrated eudialyte

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Marco E. Ciriotti
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Modular structure of highly ordered hydrated eudialyte

Messaggio da Marco E. Ciriotti » lun 04 set, 2017 22:42

▪ Rastsvetaeva, R.K., Viktorova, K.A.Aksenov, S.M. (2017): Modular Structure of Highly Ordered Eudialyte and Its Place among Hydrated Minerals of Rastsvetaevite Family. Crystallography Reports, 62, 551-557.

The crystal structure of a represent, relative of eudialyte group, which was found by A.P. Khomyakov at the Rasvumchorr mountain of the Khibiny alkaline massif (Kola Peninsula), has been studied by X-ray diffraction. The trigonal unit-cell parameters are found to be a = 14.2328(5) Å, c = 60.217(2) Å, V = 10 564.08(3) Å3, sp. gr. R3m. The structure has been refined with the isotropic and anisotropic approximation displacement parameters to the total reliability factor R = 5.6%, based on 2989 reflections with |F| > 4σ(F). The idealized formula (Z = 3) is determined as [(H3O)11Na10K5]Cа12(Na3Fe2Mn)Si4Zr6(Si48O144)(OH,Cl)5(H2O)5. The unit cell of the mineral is doubled due to the presence of two modules of different composition and structure in it (alluaivite- and kentbrooksite-like ones) and the formation of a polyhedral cluster in the kentbrooksite module. A comparison with two hydrated minerals having a modular structure shows that these minerals, being similar in their chemical composition, differ in the cation ordering over the sites of the two modules. The sample under study contains potassium in only one module, while oxonium groups are distributed in both modules but over different sites.
Marco E. Ciriotti

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