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- Title
Structure of calcinaksite KNa[Ca(H<sub>2</sub>O)][Si<sub>4</sub>O<sub>l0</sub>], the first hydrous member of the litidionite group of silicates with [Si<sub>8</sub>O<sub>20</sub>]<sup>8−</sup> tubes.
- Authors
Aksenov, Sergey M.; Rastsvetaeva, Ramiza K.; Chukanov, Nikita V.; Kolitsch, Uwe
- Abstract
Calcinaksite, KNa[Ca(H2O)][Si4Ol0], 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 heteropolyhedral framework and is characterized by the presence of several types of channels. Calcium forms distorted CaO5Ø (Ø = H2O) 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) Å2. In calcinaksite, there are three short distances between the water molecule and oxygen atoms, O w...O3 [2.844 (5) Å], O w...O9 [2.736 (4) Å] and O w...O w [2.843 (7) Å]. These distances correspond to three hydrogen bonds detected by IR data (the bands at 3340, 3170 and 3540 cm−1).
- Subjects
HYDROUS; HYDROPHILIDAE; OXYGEN compounds; SILICON compounds; SILICATES; ANISOTROPIC crystals
- Publication
Acta Crystallographica Section B: Structural Science, Crystal Engineering & Materials, 2014, Vol 70, Issue 4, p768
- ISSN
2052-5192
- Publication type
Article
- DOI
10.1107/S2052520614012992