Bowen’s Reaction Series
Rocks of varying mineral contents are often formed from the same
body of magma. As the magma cools, certain minerals crystallize first,
followed by the others in a general order of relative melting points. The
chemical composition of the magma continually changes as the process of
crystallization occurs. N.L. Bowen was the first person to discover this
principle.
1. Discontinous Reaction Series: (left branch) As minerals begin to
crystallize out of the magma, the ever-changing chemical composition
continues to form new rocks with the remaining minerals. Each
mineral/rock along the process will therefore have a different chemical
structure. Olivine – Pyroxene – Amphibole – etc…
2. Continuous Series: (right branch) The original magma is very rich in
calcium, and as it cools it forms feldspars. The feldspars gradually
change from being calcium-rich to sodium-rich. This can also occur
around large crystals – the center being Ca-rich grading into a sodiumrich exterior. The remaining magma eventually forms muscovite,
potassium feldspar and finally quartz.
3. Fractional Crystallization: A term describing the segregation and
separation of minerals due to different crystallization. The melt
becomes separate from the now solid parts of the magma, producing
igneous rocks with a wide range of compositions.
4. General crystallization order:
 Iron, magnesium, calcium to olivine, pyroxene (basalts)
 Potassium feldspar, quartz to granites
Tracy Webb – Horton High School