Abstract
We report the first natural occurrence of the Fe-analogue of akimotoite, ilmenite-structured MgSiO3, a missing phase among the predicted high-pressure polymorphs of Fe-pyroxene, with the composition (Fe2+0.48Mg0.37Ca0.04Na0.04Mn2+0.03Al0.03Cr3+0.01)Σ=1.00Si1.00O3. 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.
Highlights
The mineralogy of Earth’s deep interior represents a fascinating challenge for geoscientists
We report the discovery of the first natural occurrence of the Fe-analogue of akimotoite, with ideal formula FeSiO3
The new mineral was found in an unmelted portion of the Suizhou meteorite, and named after Russell J
Summary
The mineralogy of Earth’s deep interior represents a fascinating challenge for geoscientists. The new mineral hemleyite occurs as one subhedral crystal, about 7 × 6 × 5 μm in size, coexisting with Fe-rich clinoenstatite (which is mineralogically a clinoferrosilite but we will refer at it as Fe-rich clinoenstatite or Fe-pyroxene) and closely associated to Fe-poor clinoenstatite and forsteritic olivine (Fig. 1).
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