Fractional Crystallization of X

Pure fractional crystallization of composition X

As each grain of plagioclase is removed the residual liquid acts as a new initial liquid. The result is that for pure fractional crystallization the final solid will be a grain of plagioclase with a composition of 100% Ab - 0% An.

Batch fractional crystallization

As each batch of plagioclase grains is removed a new liquid is left over and it begins to crystallize a new plagioclase of a composition represented by the points, Pl3, Pl4, and Pl5, where the solidus and the isotherm intersect. The final solid will be a mixture of An and Ab determined by the composition of the residual liquid after the last batch of crystals has been removed.