Crystal structures of K-cymrite and kokchetavite from single-crystal X-ray diffraction
| Autor: | Yurii V. Seryotkin, Alexandr V. Romanenko, Alexander G. Sokol, Andrey V. Korsakov, Sergey V. Rashchenko, Kira A. Musiyachenko, Konstantin Glazyrin |
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| Rok vydání: | 2021 |
| Předmět: |
0303 health sciences
Materials science 030303 biophysics Crystal structure engineering.material 010502 geochemistry & geophysics 01 natural sciences 03 medical and health sciences Crystallography Geophysics Geochemistry and Petrology X-ray crystallography Cymrite engineering Single crystal 0105 earth and related environmental sciences |
| Zdroj: | American Mineralogist. 106:404-409 |
| ISSN: | 1945-3027 0003-004X |
| DOI: | 10.2138/am-2020-7407 |
| Popis: | We determined for the first time the crystal structures of high-pressure K-cymrite (KAlSi3O8⋅H2O) and its dehydrated form kokchetavite (KAlSi3O8) using single-crystal X-ray diffraction. The K-cymrite structure has been successfully refined in the hexagonal space group P6/mmm [a = 5.3361(3) Å, c = 7.7081(7) Å, V = 190.08(3) Å3, R1 = 0.036 for 127 unique observed reflections], which is in agreement with previous models from powder X-ray diffraction. In contrast, kokchetavite shows superstructural reflections, suggesting a different unit cell and a space group of P6/mcc [a = 10.5757(3) Å, c = 15.6404(6) Å, V = 1514.94(10) Å3, R1 = 0.068 for 1455 unique observed reflections]. Upon dehydration, single-crystal grains of K-cymrite transform into single-crystal grains of kokchetavite. The latter questions a previous interpretation of kokchetavite crystals in mineral inclusions as a product of direct crystallization from fluid/melt. The Raman spectrum of K-cymrite shows a strong polarization dependence, which is important in identification of the mineral inclusions. |
| Databáze: | OpenAIRE |
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