Maohokite, a post-spinel polymorph of MgFe2O4in shocked gneiss from the Xiuyancrater in China

Ming CHEN1,2, Jinfu SHU3, Xiande XIE2,4, and Dayong TAN2,4
Meteoritics & Planetary Science (in Press) Link to Article [https://doi.org/10.1111/maps.13222]
1State Key Laboratory of Isotope Geochemistry, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640Guangzhou, China
2Key Laboratory of Mineralogy and Metallogeny, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640Guangzhou, China
3Center for High Pressure Science and Technology Advanced Research, 201203 Shanghai, China
4Guangdong Provincial Key Laboratory of Mineral Physics and Materials, Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, 510640 Guangzhou, China
Published by arrangement with John Wiley & Sons

Maohokite, a post‐spinel polymorph of MgFe2O4, was found in shocked gneiss from the Xiuyan crater in China. Maohokite in shocked gneiss coexists with diamond, reidite, TiO2‐II, as well as diaplectic glasses of quartz and feldspar. Maohokite occurs as nano‐sized crystallites. The empirical formula is (Mg0.62Fe0.35Mn0.03)2+Fe3+2O4. In situ synchrotron X‐ray microdiffraction established maohokite to be orthorhombic with the CaFe2O4‐type structure. The cell parameters are = 8.907 (1) Å, = 9.937(8) Å, = 2.981(1) Å; V = 263.8 (3) Å3; space group Pnma. The calculated density of maohokite is 5.33 g cm−3. Maohokite was formed from subsolidus decomposition of ankerite Ca(Fe2+,Mg)(CO3)2 via a self‐oxidation‐reduction reaction at impact pressure and temperature of 25–45 GPa and 800–900 °C. The formation of maohokite provides a unique example for decomposition of Fe‐Mg carbonate under shock‐induced high pressure and high temperature. The mineral and its name have been approved by the Commission on New Minerals, Nomenclature and Classification of the International Mineralogical Association (IMA 2017‐047). The mineral was named maohokite after Hokwang Mao, a staff scientist at the Geophysical Laboratory, Carnegie Institution of Washington, for his great contribution to high pressure research.

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