Experiments using laser-heated diamond anvil cells combined with synchrotron X-ray diffraction and SEM–EDS chemical analyses have confirmed the existence of a complete solid solution in the MgSiO
3–MnSiO
3 perovskite system at high pressure and high temperature. The (Mg, Mn)SiO
3 perovskite produced is orthorhombic, and a linear relationship between the unit cell parameters of this perovskite and the proportion of MnSiO
3 components incorporated seems to obey Vegard’s rule at about 50 GPa. The orthorhombic distortion, judged from the axial ratios of
a/
b and
\( \sqrt{2}\,a/c, \) monotonically decreases from MgSiO
3 to MnSiO
3 perovskite at about 50 GPa. The orthorhombic distortion in (Mg
0.5, Mn
0.5)SiO
3 perovskite is almost unchanged with increasing pressure from 30 to 50 GPa. On the other hand, that distortion in (Mg
0.9, Mn
0.1)SiO
3 perovskite increases with pressure. (Mg, Mn)SiO
3 perovskite incorporating less than 10 mol% of MnSiO
3 component is quenchable. A value of the bulk modulus of 256(2) GPa with a fixed first pressure derivative of four is obtained for (Mg
0.9, Mn
0.1)SiO
3. MnSiO
3 is the first chemical component confirmed to form a complete solid solution with MgSiO
3 perovskite at the
P–
T conditions present in the lower mantle.
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