Discovery of the Fe-analogue of akimotoite in the shocked Suizhou L6 chondrite.

We report the first natural occurrence of the Fe-analogue of akimotoite, ilmenite-structured MgSiO, a missing phase among the predicted high-pressure polymorphs of Fe-pyroxene, with the composition (FeMgCaNaMnAlCr)SiO. The new mineral was approved by the International Mineralogical Association (IMA 2016-085) and named hemleyite in honour of Russell J. Hemley. It was discovered in an unmelted portion of the heavily shocked L6 Suizhou chondrite closely associated to olivine, clinoenstatite and Fe-bearing pyroxene with a composition nearly identical to that of hemleyite. We also report the first single-crystal X-ray diffraction study of a Si-bearing, ilmenite-structured phase. The fact that hemleyite formed in a meteorite exposed to high pressures (<20 GPa) and temperatures (<2000 °C) during impact-induced shocks indicates that it could play a crucial role at the bottom of the Earth's mantle transition zone and within the uppermost lower mantle.