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Atomic Positional Parameters
Mg 4a 0.0000 0.0000 0.0000
O  4a 0.5000 0.5000 0.5000

Reference
E Schiebold (1921) Zeitschrift fuer Kristallographie, Kristallgeometrie, Kristallphysik, Kristallchemie, 56, 430

Mineral Chemistry
Periclase (MgO), which has a similar structure to that of halite, is usually formed in high-temperature metamorphism and decarbonation of dolomites and magnesian limestones. Up to 8 weight percent of FeO may substitute for MgO in this phase.

Characterisation of the behaviour of (Mg,Fe)O solid solutions is crucial for understanding the lower mantle, and many experimental and theoretical studies of MgO under lower mantle conditions have been made. It is likely that the composition of the lower mantle of the earth is made up of a silicate perovskite (Mg_0.9Fe_0.1)SiO₃, with several percent Al₂O₃, coexisting with (Mg,Fe)O - magnesiowüstite.