Bowen's reaction series describes the formation of minerals as magma cools. Rocks formed from magma are igneous rocks, and minerals crystallize as magma cools. The temperature of the magma and the rate of cooling determine which minerals are stable (i.e., which minerals can form) and the size of the mineral crystals formed (i.e., texture). The slower a magma cools, the larger crystals can grow.

Named after geologist Norman L. Bowen (1887–1956), Bowen's reaction series allows geologists to predict chemical composition and texture based upon the temperature of a cooling magma.

Bowen's reaction series is usually diagramed as a "Y" with horizontal lines drawn across the "Y." The first horizontal line—usually placed just above the top of the "Y"—represents a temperature of 3,272°F (1,800°C). The next horizontal line, represents a temperature of 2,012°F (1,100°C) and is located one-third...