The high-pressure phase transformation and breakdown of MgFe2O4

High-Fe (Mg, Fe)O inclusion in diamond apparently from the lowermost mantle

“…Using the composition of mw immediately adjacent to mf crystals and partitioning the Fe signal appropriately to maintain charge balance, we calculated that mf has the approximate cation composition of (Mg 0.14 Fe 0 Given that this specimen may have a very deep origin, we have carefully examined the mf crystals at very high magnification in TEM to investigate whether the current spinel form was the primary precipitate, or whether the high-pressure polymorph of mf may have precipitated first. Because the composition of the actual phase present is approximately (Mg 0.5 Fe 0.5 )Fe 2 O 4 , it is not clear whether the phase of this composition would crystallize at extreme pressures in the CaMn 2 O 4 structure (like pure magnesium ferrite, MgFe 2 O 4 ) (Andrault and Bolfan-Casanova, 2001;Levy et al, 2004;Winell et al, 2006), or whether the situation might be more complicated. Recent work has shown that pure magnetite decomposes into a mixture of Fe 2 O 3 (hematite) and the newly-discovered Fe 4 O 5 structure (Lavina et al, 2011;Woodland et al, 2012).…”

Maohokite, a post‐spinel polymorph of MgFe2O4 in shocked gneiss from the Xiuyan crater in China

“…The strong band at 686 cm −1 and some weak bands at 554, 478, 328, and 210 cm −1 are attributed to magnesioferrite (Winell et al. ), and the strong band at 602 cm −1 to maohokite, in comparison to the Raman spectrum of post‐spinel polymorph of FeCr 2 O 4 (Chen et al. ).…”

“…The post‐spinel transformation in MgFe 2 O 4 under high‐pressure and high‐temperature conditions has been observed experimentally in the laser‐heated diamond anvil cell above 20 GPa (Mao and Bell ; Andrault and Bolfan‐Casanova ; Winell et al. ). However, no post‐spinel phase of MgFe 2 O 4 has been previously found in nature.…”

“…Magnesioferrite, MgFe 2 O 4 , is a Fe 3+ -rich member of the spinel group, which has been found in kimberlites and carbonatites as well as volcanic fumaroles. The post-spinel transformation in MgFe 2 O 4 under high-pressure and high-temperature conditions has been observed experimentally in the laser-heated diamond anvil cell above 20 GPa (Mao and Bell 1975;Andrault and Bolfan-Casanova 2001;Winell et al 2006). However, no post-spinel phase of MgFe 2 O 4 has been previously found in nature.…”

“…The strong band at 1086 cm À1 and weak band at 279 cm À1 can be assigned to calcite (Sun et al 2014). The strong band at 686 cm À1 and some weak bands at 554, 478, 328, and 210 cm À1 are attributed to magnesioferrite (Winell et al 2006), and the strong band at 602 cm À1 to maohokite, in comparison to the Raman spectrum of post-spinel polymorph of FeCr 2 O 4 (Chen et al 2003). Raman spectra of both magnesioferrite and magnetite usually display a strong and well-defined A 1 g band at approximately 670 cm À1 and 700 cm À1 , respectively (D'Ippolito et al 2015).…”