Dissymmetrization in Eudialyte-Group Minerals. II: Role of the M2-Position in Ordered P3-Model of the Structure of a Zr-Rich Member of the Eudialyte Group
R. K. Rastsvetaeva, S. M. Aksenov, V. M. Gridchina, N. V. Chukanov
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引用次数: 0
Abstract
A re-study of the crystal structure of low-calcium and high-zirconium eudialyte from the Khibiny Mountains of Kola Peninsula has revealed new features of its structure, which decrease the symmetry of the mineral. The ordering of Ca, Fe, Mn, and Na atoms in octahedra of six-membered rings, as well as Zr and Na atoms in M2 positions at the centers of square pyramids, with a common base, formed by the edges of these octahedra, has been established with the P3 symmetry. The trigonal unit cell parameters are a = 14.222(3) Å, c = 30.165(5) Å, and V = 5283.9 Å3. Taking into account the new data, the studied low-calcium eudialyte can be assigned to the subtype of oneillite or raslakite, being a high-zirconium variety of the latter. The study of the structure of this mineral in rhombohedral symmetry (sp. gr. R3m and R3) and trigonal Р3 symmetry has shown that the decrease in symmetry of the structural model of low-calcium representatives of the eudialyte group makes it possible to clarify the nature of ordering of the cations occupying key framework positions.
重新研究了科拉半岛希比尼山低钙高锆电解液的晶体结构,揭示了其结构的新特征,降低了矿物的对称性。六元环八面体中Ca、Fe、Mn和Na原子的排列顺序,以及由八面体边缘形成的正方形金字塔中心M2位置上的Zr和Na原子的排列顺序,已经建立了P3对称。三角单元胞参数为a = 14.222(3) Å, c = 30.165(5) Å, V = 5283.9 Å3。考虑到新的数据,所研究的低钙电解质可归属于oneillite或raslakite亚型,是后者的高锆品种。对这种矿物的菱面体对称(sp. gr. R3m和R3)和三角Р3对称结构的研究表明,低钙双电解质基代表的结构模型对称性的降低使得澄清占据关键框架位置的阳离子的有序性质成为可能。
期刊介绍:
Crystallography Reports is a journal that publishes original articles short communications, and reviews on various aspects of crystallography: diffraction and scattering of X-rays, electrons, and neutrons, determination of crystal structure of inorganic and organic substances, including proteins and other biological substances; UV-VIS and IR spectroscopy; growth, imperfect structure and physical properties of crystals; thin films, liquid crystals, nanomaterials, partially disordered systems, and the methods of studies.