New silicate perovskites

The previously reported non‐quenchable phases of the compositions of diopside and omphacite, or the diopside‐II phase, have been observed to crystallize in the cubic perovskite structure at pressures greater than ∼230 kbar and at ∼1000°C by in situ experiments using a gasketed diamond‐anvil cell coupled with laser heating. The lattice parameter for the perovskite phase of (Ca 0.5 Mg 0.5 )SiO 3 is a = 3.437 ± 0.004Å and that of ½ (0.75CaMgSi 2 O 6 ·0.25NaAlSi 2 O 6 ) a = 3.492 ± 0.004Å at pressure range 230‐245 kbar and room temperature. Diopside‐II is the most likely host of both Ca and Na, and probably the second most abundant mineral phase, in the lower mantle.

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