Crystal structures of iron oxide FeO₂ and derived compounds. (a) FeO₂- Pa 3 ¯ at 76 GPa;^[17] (b) FeO₂H- Pa 3 ¯ at 100 GPa;^[21] (c) FeO₂He at 100 GPa.^[22] Fe (O,H,He) atoms are gold (red, pink, white) spheres, respectively.