Maohokite, a post‐spinel polymorph of MgFe2O4 in shocked gneiss from the Xiuyan crater in China. (30th November 2018)

• Record Type: Journal Article
• Authors: Chen, Ming; Shu, Jinfu; Xie, Xiande; Tan, Dayong
• Is Part Of: Meteoritics & planetary science. Volume 54:Number 3(2019)
• Page Start: 495
• Page End: 502
• Publication Date: 2018-11-30
• Subjects: Meteorites -- Periodicals; Planetology -- Periodicals; 523.4
• DOI: 10.1111/maps.13222
• Languages: English
• ISSNs: 1086-9379

Abstract

Abstract: Maohokite, a post‐spinel polymorph of MgFe2 O4, 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 (Mg0.62 Fe0.35 Mn0.03 ) 2+ Fe 3+ 2 O4 . In situ synchrotron X‐ray microdiffraction established maohokite to be orthorhombic with the CaFe2 O4 ‐type structure. The cell parameters are a = 8.907 (1) Å, b = 9.937(8) Å, c = 2.981(1) Å; V = 263.8 (3) Å 3 ; space group Pnma . The calculated density of maohokite is 5.33 g cm −3 . Maohokite was formed from subsolidus decomposition of ankerite Ca(Fe 2+, 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.