Synthesis and crystal structure of chromium-bearing anhydrous wadsleyite
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A chromium-bearing wadsleyite (Cr-Wad) was synthesized in the model system Mg2SiO4–MgCr2O4 at 14 GPa and 1600 °C and studied from the chemical and structural point of views. Microprobe data gave the formula Mg1.930Cr0.120Si0.945O4, on the basis of 4 oxygen atoms. The crystal structure has been studied by single-crystal X-ray diffraction. The orthorhombic unit-cell parameters are: a = 5.6909(5) Å, b = 11.4640(10) Å, c = 8.2406(9) Å, V = 537.62(9) Å3, Z = 8. The structure, space group Imma, was refined to R 1 = 5.99% in anisotropic approximation using 1135 reflections with F o > 4σ(F o) and 43 parameters. Chromium was found to substitute for both Mg at the octahedral sites and Si at the tetrahedral site, according to the reaction VIMg2+ + IVSi4+ = VICr3+ + IVCr3+. On the whole, the structural topology is nearly identical to that of pure wadsleyite. The successful synthesis of Cr-Wad may be important for the thermobarometry of mantle phase associations.
KeywordsWadsleyite High-pressure experiments Single-crystal X-ray diffraction Chromium Earth’s mantle
The research was supported by the Russian Science Foundation (project no. 17-17-01169 to AB and ES). Structural studies were partly supported by the Foundation of the President of the Russian Federation (grant no. MK-1277.2017.5 to ES).
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