Extraordinary structural complexity of ilmajokite: a multilevel hierarchical framework structure of natural origin.

The crystal structure of ilmajokite, a rare Na-K-Ba-Ce-titanosilicate from the Khibiny mountains, Kola peninsula, Russia, has been solved using single-crystal X-ray diffraction data. The crystal structure is based on a 3D titanosilicate framework consisting of trigonal prismatic titanosilicate (TPTS...

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Bibliographic Details
Published in:IUCrJ
Main Authors: Zolotarev, Andrey A, Krivovichev, Sergey V, Cámara, Fernando, Bindi, Luca, Zhitova, Elena S, Hawthorne, Frank, Sokolova, Elena
Format: Article in Journal/Newspaper
Language:English
Published: International Union of Crystallography 2020
Subjects:
ilmajokite
structural complexity
structural hierarchy
titanosilicates
kola peninsula
Online Access:https://doi.org/10.1107/S2052252519016622
https://pubmed.ncbi.nlm.nih.gov/31949912
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC6949600/
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Summary:The crystal structure of ilmajokite, a rare Na-K-Ba-Ce-titanosilicate from the Khibiny mountains, Kola peninsula, Russia, has been solved using single-crystal X-ray diffraction data. The crystal structure is based on a 3D titanosilicate framework consisting of trigonal prismatic titanosilicate (TPTS) clusters centered by Ce3+ in [9]-coordination. Four adjacent TPTS clusters are linked into four-membered rings within the (010) plane and connected via ribbons parallel to 101. The ribbons are organized into layers parallel to (010) and modulated along the a axis with a modulation wavelength of csinβ = 32.91 Å and an amplitude of ∼b/2 = 13.89 Å. The layers are linked by additional silicate tetrahedra. Na+, K+, Ba2+ and H2O groups occur in the framework cavities and have different occupancies and coordination environments. The crystal structure of ilmajokite can be separated into eight hierarchical levels: atoms, coordination polyhedra, TPTS clusters, rings, ribbons, layers, the framework and the whole structure. The information-based analysis allows estimation of the complexity of the structure as 8.468 bits per atom and 11990.129 bits per cell. According to this analysis, ilmajokite is the third-most complex mineral known to date after ewingite and morrisonite, and is the most complex mineral framework structure, comparable in complexity to paulingite-(Ca) (11 590.532 bits per cell).

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