IMA 2017-047 = maohokite

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Marco E. Ciriotti
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IMA 2017-047 = maohokite

Messaggio da Marco E. Ciriotti » lun 10 dic, 2018 11:20

▪ Chen, M., Shu, J., Xie, X., Tan, D. (2018): Maohokite, a post-spinel polymorph of MgFe2O4 in shocked gneiss from the Xiuyan crater in China. Meteoritics and Planetary Science, 2018, 1-8.

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 a = 8.907 (1) A, b = 9.937(8) A, c = 2.981 (1) A; V = 263.8 (3) A3; space group Pnma. The calculated density of maohokite is 5.33 g cm3. 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,
Marco E. Ciriotti

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