New Data on the Structure of Eudialyte-Group Mineral Sergevanite. Ordered and Disordered Structures of Minerals with Complex Composition

• Published in: Crystallography reports 2022-12, Vol.67 (7), p.1105-1113
• Main Author: Rastsvetaeva, R. K.
• Format: Article
• Language: English
• Subjects: Composition; Crystal structure; Crystallography and Scattering Methods; Electron probe microanalysis; Minerals; Physics; Physics and Astronomy; Reliability aspects; Structure of Inorganic Compounds
• ISSN: 1063-7745; 1562-689X
• DOI: 10.1134/S1063774522070471

The structure of a new eudialyte-group mineral sergevanite has been investigated using X-ray diffraction (XRD) analysis and electron probe microanalysis. The parameters of an elementary trigonal cell of the mineral are found to be a = 14.2179(1) Å, c = 30.3492(3) Å, and V = 5313.1(7) Å 3 ; sp. gr. R 3. The crystal structure is refined to the final reliability factor R = 2.74% in the anisotropic approximation of atomic displacements using 4870 reflections with F > 3σ( F ). The idealized formula of the mineral ( Z = 3) is (Na 12 KH 3 O)[Ca 3 (Mn 2 Ca)](Na 2 Fe)Zr 3 Ti 0.5 Si 25.5 O 72 OH 2 ⋅(H 2 O) 2 . The approaches to study the structural features of eudialyte-group minerals are discussed. In the structures of these minerals, the complex composition is ordered over statistically occupied sites in correspondence with the crystallochemical properties of atoms (ions) and formation conditions, both thermodynamic (temperature and pressure) and kinetic (process rate and duration). This information is absent for disordered topological structures with mixed unsplit sites.