2D X-ray diffraction map of the (Mg_0.5Fe_0.5)O sample heated in a pure H medium at 23 GPa and 2450 K. The mapping was conducted after the recovery of the sample at 1 bar and 300 K inside a diamond-anvil cell. The green dashed circle indicates the hot spot center. (a) Fe content in (Mg,Fe)O was calculated from the unit-cell volume using a linear relationship between the volume and the Fe content (Jackson & Rigden 1996). (b) Intensity ratio between Fe metal (bcc converted from FeH _x ) and (Mg,Fe)O. (c) Intensity ratio between brucite and (Mg,Fe)O.