Bowen's Reaction Series

Bowen's reaction series describes the sequence in which different minerals crystallize out of a cooling body of magma, explaining how a single parent magma can give rise to the many different types of igneous rock found in nature. Canadian petrologist Norman L. Bowen developed the series through experimental laboratory work published mainly across the 1910s and 1920s, presenting it most fully in his 1928 book The Evolution of the Igneous Rocks. The series describes two parallel branches as magma cools: a discontinuous branch, in which iron- and magnesium-rich minerals crystallize in a fixed order from olivine through pyroxene, amphibole and biotite mica as temperature drops, and a continuous branch, in which plagioclase feldspar crystallizes continuously while its own composition shifts gradually from calcium-rich to sodium-rich; both branches converge toward the final crystallization, at the lowest temperatures, of potassium feldspar, muscovite mica and quartz. Bowen's work explained how the process of fractional crystallization, the progressive removal of already-crystallized minerals from the remaining melt, could account for the wide compositional diversity of igneous rocks even when they all ultimately derive from chemically similar parent magmas.