A sequence of mineral reactions each of which takes place at a specific temperature during the cooling of a magma. A high-temperature mineral will remain in equilibrium with a cooling magma until it reaches its reaction temperature. At this point the mineral completely reacts with the melt and dissolves away to produce a new mineral in equilibrium with the melt. This second mineral remains in equilibrium with the magma as the magma continues to cool until its reaction temperature is also reached. The process then repeats itself. The principle of discontinuous reaction was first advanced by Norman Bowen in 1928. In sub-alkaline magmas the discontinuous reaction olivine-pyroxene-amphibole-biotite is commonly observed.