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Super‐Earths ranging up to 10 Earth masses (M_E) with Earth‐like density are common among the observed exoplanets thus far, but their measured masses and radii do not uniquely elucidate their internal structure. Exploring the phase transitions in the Mg‐silicates that define the mantle‐structure of super‐Earths is critical to characterizing their interiors, yet the relevant terapascal conditions are experimentally challenging for direct structural analysis. Here we investigated the crystal chemistry of Fe₃O₄as a low‐pressure analog to Mg₂SiO₄between 45–115 GPa and up to 3000 K using powder and single crystal X‐ray diffraction in the laser‐heated diamond anvil cell. Between 60–115 GPa and above 2000 K, Fe₃O₄adopts an 8‐fold coordinated Th₃P₄‐type structure (I‐43d,Z = 4) with disordered Fe²⁺and Fe³⁺into one metal site. This Fe‐oxide phase is isostructural with that predicted for Mg₂SiO₄above 500 GPa in super‐Earth mantles and suggests that Mg₂SiO₄can incorporate both ferric and ferrous iron at these conditions. The pressure‐volume behavior observed in this 8‐fold coordinated Fe₃O₄indicates a maximum 4% density increase across the 6‐ to 8‐fold coordination transition in the analog Mg‐silicate. Reassessment of the FeO—Fe₃O₄fugacity buffer considering the Fe₃O₄phase relationships identified in this study reveals that increasing pressure and temperature to 120 GPa and 3000 K in Earth and planetary mantles drives iron toward oxidation.