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Understanding giant impacts requires accurate description of how extreme pressures and temperatures affect the physical properties of the constituent materials. Here, we report shock experiments on two polymorphs of MgSiO 3: enstatite and bridgmanite (perovskite) crystals. We obtain pressure‐density shock equation of state to 14 Mbar and more than 9 g/cm 3, a 40% increase in density from previous data on MgSiO 3. Density‐functional‐theory molecular dynamics (DFT‐MD) simulations provide predictions for the shock Hugoniot curves for bridgmanite and enstatite and suggest that the Grüneisen parameter decreases with increasing density. The good agreement between the simulations and the experimental data, including for the shock temperature along the enstatite Hugoniot reveals that DFT‐MD simulations reproduce well the behavior of dense fluid MgSiO3. We also reveal a high optical reflectance indicative of a metal‐like electrical conductivity which supports the hypothesis that magma oceans may contribute to planetary magnetic field generation. Plain Language Summary: Deciphering the evolution of the early Earth requires a detailed understanding of the history of our planet formation and evolution. Much like for other planets in the solar system and beyond, giant impacts are thought to have played a key role in the Earth history including the formation of the moon and the intense climatic perturbations leading to the Cretaceous‐Paleogene extinction event. Computer simulations of giant impact are now becoming increasingly accurate thanks to ever‐growing supercomputing capabilities worldwide. Here we report new shock wave experiments on two different kinds of the Earth mantle's most abundant mineral MgSiO 3, together with simulations based on quantum theory of condensed matter. We find that under intense shockwave compression of several million atmospheres, shock‐induced heating and compression together transform the rocky minerals into dense, shiny fluid able to conduct electrical current and therefore perhaps contribute to magnetic field generation by dynamo effect in the early stages of the evolution of rocky planets and exoplanets. Key Points: Bridgmanite was shock compressed to the conditions of giant impacts that dominated the final phase of the solar system formationDFT molecular dynamics simulations reproduce well the experimental data under such extreme P‐T conditions relevant for giant impact modelsDense fluid MgSiO3 exhibits a metal‐like electrical conductivity which indicates that magma oceans may generate planetary magnetic field [ABSTRACT FROM AUTHOR]