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

• Published in: IUCrJ
• Main Authors: Zolotarev, Andrey A., Krivovichev, Sergey V., Cámara, Fernando, Bindi, Luca, Zhitova, Elena S., Hawthorne, Frank, Sokolova, Elena
• Format: Text
• Language: English
• Published: International Union of Crystallography 2020
• Subjects: Research Papers; Khibiny; Kola Peninsula; kola peninsula
• Online Access: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6949600/; https://doi.org/10.1107/S2052252519016622

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 Ce(3+) 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(+), Ba(2+) and H(2)O 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).