Crystal structure of magnesioferrikatophorite
| Autor: | Yu. S. Lebedeva, Giovanni Ferraris, Igor V. Pekov, D. Yu. Pushcharovskii, Gabriella Ivaldi, Alla A. Novakova |
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| Rok vydání: | 2003 |
| Předmět: | |
| Zdroj: | Crystallography Reports. 48:16-23 |
| ISSN: | 1562-689X 1063-7745 |
| DOI: | 10.1134/1.1541736 |
| Popis: | The crystal structure of the Na,Ca-amphibole magnesioferrikatophorite found in carbonatites from the Turiy Cape (Kola Peninsula) was refined (Siemens P4 diffractometer, λMoK α radiation, 1481 independent reflections with |F|>4σ(F), anisotropic refinement, R(F) = 0.039). The parameters of the monoclinic unit cell are a = 9.875(5) A, b = 18.010(8) A, c = 5.309(3) A, β = 104.39(5)°, sp. gr. C2/m, Z = 2. The distribution of the cations over the crystallographically nonequivalent M(1–4)-positions was revealed by Mossbauer spectroscopy and X-ray diffraction analysis. The character of splitting of the A-position correlates with the characteristic features of the magnesioferrikatophorite composition. The resulting structural formula (Na0.87K0.13)Σ = 1 · (Na1.18Ca0.82)Σ = 2(Mg1.41Fe 0.42 3+ Ti 0.17 4+ )Σ= 2 Fe 1.31 3+ Mg0.69)Σ = 2(Mg0.60Fe 0.38 2+ Mn0.02)Σ = 1(Si3.16Al0.84)Σ = 4 · Si4O22(O1.05OH0.66F0.29)Σ= 2 agrees well with the electron microprobe analysis data. Based on the zonal character of the crystal and high Fe 3+ content, the conditions of crystallogenesis are defined as oxidative against the background of a decrease in the Na potential in the course of the evolution of a mineral-forming system. |
| Databáze: | OpenAIRE |
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