A process by which a generally homogeneous chondritic body containing mostly metal, silicates and sulfides will melt and form distinct (differentiated) layers of different densities.   When the melting process continues for a long enough period of time, the once chondritic body will re-partition into layers of different composition including a metallic core and a silicate-rich mantle and crust. A principal source of heat driving the melting process was the radioactive decay of  26Al, an  isotope of aluminum, into a stable nuclide of 26Mg.

Heating of the primordial mixture of stony minerals, metals, and sulfides produced dense metallic liquids which sank to become planetary or asteroidal cores. Less dense silicate magmas rose and solidified to become basaltic or, on Earth, granitic crust. Material with neutral buoyancy formed planetary mantles.

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