Magma Ocean

Completely molten surfaces of terrestrial planets or moons that formed soon after accretion. Samples returned by the Apollo missions provide evidence of a lunar magma ocean, crystallization of which produced a stratified Moon with a low-density crust formed by accumulation of the mineral plagioclase overlying a higher density mantle of olivine and pyroxene.

Image Source: en.wikipedia.org

Some or all content above used with permission from J. H. Wittke.