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 (Ca0.5Md0.5)SiO3 is a=3.437¿0.004 ¿ and that of 1/2(0.75CaMgSi2O6⋅0.25NaAlSi2O6) a=3.492¿0.004 ¿ 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. ¿ American Geophysical Union 1987