In geology, the word "differentiate" refers specifically to a chemical process changing the composition of a body of rock or magma away from an average composition. There are two common kinds of geologic differentiation. They are:
Chemical differentiation: Here, various elements or oxides are preferentially selected from a more homogenous parent body, based upon minimizing thermodynamic energy in the mixture. This process resulted in the chemical distinctions between the Earth's crust and mantle, as the crust is formed of the more easily melted portions of the mantle.
Physical differentiation: In this case, actual physical processes separate out different components of a mixture. Most commonly, heavier components of a magma-rock mixture settle to the bottom gravitationally. This process caused the Earth to separate into a nickel-iron core and a more siliceous mantle and crust.
In the planetary sciences and the study of meteorites, differentiation from the solar norm indicates that a rock originated from a sufficiently large parent body to induce melting.