Structure of calcinaksite KNa[Ca(H₂O)][Si₄O_l0], the first hydrous member of the litidionite group of silicates with [Si₈O₂₀]₈- tubes

Author(s)

Sergey M. Aksenov, Ramiza K. Rastsvetaeva, Nikita V. Chukanov, Uwe Kolitsch

Abstract

Calcinaksite, KNa[Ca(H

₂O)][Si

₄O

₁₀], a new natural member of the litidionite group, was found in a calcic xenolith from alkaline basalt of the Bellerberg volcano, Eastern Eifel region, Rhineland-Palatinate, Germany. The crystal structure has been studied based on single-crystal X-ray diffraction data. Triclinic unit-cell parameters are: a = 7.021 (2), b = 8.250 (3), c = 10.145 (2) Å, α = 102.23 (2), β = 100.34 (2), γ = 115.09 (3)°, space group . The structure model was determined by the 'charge-flipping' method and refined to R = 0.0527 in anisotropic approximation using 3057 I > 3σ(I). Calcinaksite is a hydrous calcium-dominant litidionite-group mineral. The crystal structure of calcinaksite (like other litidionite-group minerals and related compounds) is based on a heteropoly-hedral framework and is characterized by the presence of several types of channels. Calcium forms distorted CaO

₅Ø (Ø = H

₂O) octahedra while Na forms NaO5 square pyramids. Nine-coordinated K atoms are located in a channel extending along [010]. Water molecules occupy a channel running along the [100] direction and are characterized by a rather high equivalent isotropic displacement parameter of 0.053 (2) Å

². In calcinaksite, there are three short distances between the water molecule and oxygen atoms, Ow⋯O3 [2.844 (5) Å], Ow⋯O9 [2.736 (4) Å] and Ow⋯Ow [2.843 (7) Å]. These distances correspond to three hydrogen bonds detected by IR data (the bands at 3340, 3170 and 3540 cm

^-1).

Organisation(s)

Department of Mineralogy and Crystallography

External organisation(s)

Russian Academy of Sciences

Journal

Acta Crystallographica. Section B: Structural Science

Volume

70

Pages

768-775

No. of pages

8

ISSN

0108-7681

DOI

https://doi.org/10.1107/S2052520614012992

Publication date

07-2014

Peer reviewed

Yes

Austrian Fields of Science 2012

105116 Mineralogy, 104017 Physical chemistry, 105113 Crystallography

Keywords

ASJC Scopus subject areas

Electronic, Optical and Magnetic Materials, Metals and Alloys, Materials Chemistry, Atomic and Molecular Physics, and Optics

Portal url

https://ucrisportal.univie.ac.at/en/publications/c6f65c46-653b-47f7-9147-032f120ffa1f