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Abstract <p>The crystal structure of ikranite, low-calcium and high-oxonium eudialyte-group member, was repeatedly studied by the X-ray diffraction method within the space group <i>Р</i>3. The trigonal unit-cell parameters are <i>a =</i> 14.17521(8) Å, <i>c =</i> 30.1673(2) Å, <i>V</i> = 5249.60(6) Å<sup>3</sup>. The crystal structure of ikranite with the idealized formula (Na,H<sub>3</sub>O)<sub>15</sub>(Ca,Mn,<i>REE</i>)<sub>6</sub>Fe<InlineEquation ID="IEq1"> <EquationSource Format="TEX">\(_{2}^{{3 + }}\)</EquationSource> <!--Cryst2560150Rastsvetaeva-m1--> </InlineEquation>Zr<sub>3</sub>(<InlineEquation ID="IEq2"> <EquationSource Format="TEX">\(\square \)</EquationSource> <!--Cryst2560150Rastsvetaeva-m2--> </InlineEquation>,Zr)(<InlineEquation ID="IEq3"> <EquationSource Format="TEX">\(\square \)</EquationSource> <!--Cryst2560150Rastsvetaeva-m3--> </InlineEquation>,Si)Si<sub>24</sub>O<sub>66</sub>(O,OH)<sub>6</sub>Cl·<i>n</i>H<sub>2</sub>O, <i>n</i> = 2–3, was studied previously using a limited set of diffraction data within the sp. gr. <i>R</i>3<i>m</i>. Full experiment with refining the structural model in the sp. gr. <i>Р</i>3 (158 unique positions, <i>R</i> = 0.046, 4912 unique reflections with <i>F</i> &gt; 3σ(<i>F</i>)) revealed some additional structural features of this mineral, in particular, the existence of a six-membered ring of edge-sharing CaO<sub>6</sub> and NaO<sub>6</sub> octahedra, along with a ring from alternating CaO<sub>6</sub> and MnO<sub>6</sub> octahedra, established previously in some eudialyte-group minerals of the oneillite type.</p>

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Dissymmetrization in Eudialyte-Group Minerals. VIII: Refinement of the Ikranite Crystal Structure in the Framework of the P3 Model

  • 期刊论文

  • 发表日期：

    2026年2月1日

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  • R. K. Rastsvetaeva,
  • V. M. Gridchina,
  • N. V. Chukanov,
  • S. M. Aksenov

摘要

Abstract

The crystal structure of ikranite, low-calcium and high-oxonium eudialyte-group member, was repeatedly studied by the X-ray diffraction method within the space group Р3. The trigonal unit-cell parameters are a = 14.17521(8) Å, c = 30.1673(2) Å, V = 5249.60(6) Å3. The crystal structure of ikranite with the idealized formula (Na,H3O)15(Ca,Mn,REE)6Fe \(_{2}^{{3 + }}\) Zr3( \(\square \) ,Zr)( \(\square \) ,Si)Si24O66(O,OH)6Cl·nH2O, n = 2–3, was studied previously using a limited set of diffraction data within the sp. gr. R3m. Full experiment with refining the structural model in the sp. gr. Р3 (158 unique positions, R = 0.046, 4912 unique reflections with F > 3σ(F)) revealed some additional structural features of this mineral, in particular, the existence of a six-membered ring of edge-sharing CaO6 and NaO6 octahedra, along with a ring from alternating CaO6 and MnO6 octahedra, established previously in some eudialyte-group minerals of the oneillite type.