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Maohokite, a post‐spinel polymorph of MgFe 2 O 4 in shocked gneiss from the Xiuyan crater in China
Author(s) -
Chen Ming,
Shu Jinfu,
Xie Xiande,
Tan Dayong
Publication year - 2019
Publication title -
meteoritics and planetary science
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.09
H-Index - 100
eISSN - 1945-5100
pISSN - 1086-9379
DOI - 10.1111/maps.13222
Subject(s) - spinel , orthorhombic crystal system , geology , mineral , geochemistry , mineralogy , crystallography , gneiss , crystal structure , chemistry , materials science , metallurgy , metamorphic rock , paleontology
Maohokite, a post‐spinel polymorph of MgFe 2 O 4 , was found in shocked gneiss from the Xiuyan crater in China. Maohokite in shocked gneiss coexists with diamond, reidite, TiO 2 ‐ II , as well as diaplectic glasses of quartz and feldspar. Maohokite occurs as nano‐sized crystallites. The empirical formula is (Mg 0.62 Fe 0.35 Mn 0.03 ) 2+ Fe 3+ 2 O 4 . In situ synchrotron X‐ray microdiffraction established maohokite to be orthorhombic with the CaFe 2 O 4 ‐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)( CO 3 ) 2 via a self‐oxidation‐reduction reaction at impact pressure and temperature of 25–45 GP a 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.