Crystal structure of Cl-deficient analogue of taseqite from Odikhincha Massif

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Marco E. Ciriotti
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Crystal structure of Cl-deficient analogue of taseqite from Odikhincha Massif

Messaggio da Marco E. Ciriotti » mer 13 giu, 2018 14:33

Referenza:
▪ Rastsvetaeva, R.K., Chukanov, N.V., Zaitsev, V.A., Aksenov, S.M., Viktorova, K.A. (2018): Crystal Structure of Cl-Deficient Analogue of Taseqite from Odikhincha Massif. Crystallography Reports, 63, 349-357.

Abstract:
An eudialyte group mineral, found in pegmatites of the Odikhincha massif (the northern part of the Siberian platform), has been investigated using X-ray diffraction, IR spectroscopy, and Raman spectroscopy. The mineral is characterized by a high strontium content and a low chlorine content. It has a trigonal unit cell with the following parameters: a = 14.2700(6) Å and c = 30.057(1) Å; V = 5300.6(1) Å3; sp. gr. R3m. The structure has been refined to R = 0.047 in the anisotropic approximation of atomic displacements using 1697F > 4σ(F). The idealized formula (Z = 3) was found to be Na12Sr2Ca6Fe2+3Zr3NbSi25O72(OH,O)4Cl(Н2О)0.2. The chemical composition and structure of this mineral are close to those of taseqite; however, it differs from the holotype sample by a low chlorine content and peculiarities of cation distribution over basic structure sites. A comparative analysis of strontium-rich eudialytes has revealed their important crystallochemical feature: selective concentration of strontium in the N4 site. Thus, taseqite, along with heterophyllosilicates, may play a role of strontium concentrator in agpaitic pegmatites.
Marco E. Ciriotti

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