New Data on the Isomorphism in Eudialyte-Group Minerals. ХI: Crystal Structure of a Potentially New Mineral—A Case of Complete Substitution of Fe2+with in the Eudialyte-Type Structure

• Published in: Crystallography reports 2022, Vol.67 (2), p.166-171
• Main Authors: Rastsvetaeva, R. K., Chukanov, N. V., Pekov, I. V., Varlamov, D. A., Kazheva, O. N.
• Format: Article
• Language: English
• Subjects: Coordination numbers; Crystal structure; Crystallography and Scattering Methods; Iron; Isomorphism; Massifs; Minerals; Physics; Physics and Astronomy; Reliability aspects; Structure of Inorganic Compounds; Unit cell; Zirconium
• ISSN: 1063-7745; 1562-689X
• DOI: 10.1134/S1063774522020134

The crystal structure and crystallochemical features of a Fe-deficient zirconium-rich analog of eudialyte from the Lovozero alkaline massif (Kola peninsula) have been investigated. The unit-cell parameters of the mineral are found to be a = 14.198(1) Å, c = 30.380(1) Å, and V = 5303.9(1) Å 3 ; sp. gr. R 3 m . The crystal structure is refined to the final reliability factor R = 4.2% in the anisotropic approximation of atomic displacements using 3174 reflections with F > 3σ( F ). The crystallochemical formula of the mineral ( Z = 3) is [Na 10.38 (H 3 O,H 2 O) 2.79 Ce 0.45 Sr 0.4 K 0.2 ][Ca 3.9 Mn 1.2 Fe 0.9 ][ VII Na V Zr 0.87 ]Zr 3 [Si 1.48 Ti 0.31 Nb 0.21 ][Si 24 O 72 ](OH) 2.9 (H 2 O) 1.26 (Cl, S) 0.94 (Roman numerals are the coordination numbers (CNs) of cations at the M 2 key site). The regularities of block isomorphism in the vicinity of the M 2 site in the structure of the mineral under study and related eudialyte-group minerals are discussed.