Molecular dynamics simulations of MgO based on interionic potentials derived from modified electron-gas calculations have been used to model crystallization of periclase from a supercooled liquid. The phase transition between supercooled liquid and crystal is signaled by a large decrease in the enthalpy of the system, a decrease in calculated pressure, and a [4>Mg→[6>Mg coordination change. Nucleation is nearly instantaneous above a critical density corresponding to the transformation to octahedral coordination in the supercooled liquid. Crystal growth enhances diffusion during the simulation as ions in the liquid move in a direction consistent with the crystal orientation at the liquid-solid interface. Ions do not detach from the crystal surface once they are bonded to the growing crystal, suggesting that growth is in the diffusion-limited regime. ¿ American Geophysical Union 1993