- The process by which chemically different igneous rocks, such as basalt and granite, can form from the same initial magma. Magmatic differentiation can occur by the chemical reaction between the magma and the first crystals to solidify out of it, or by the physical separation of the first crystals that form from the remaining magma, either through settling to the bottom of a magma chamber or through crustal deformations that cause the remaining magma to be squeezed out to cool in veins and dikes.
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