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3.2.4 Two component phase diagram: diopside–anorthite
anorthite228diopside26
ssss1 Diopside–anorthite phase diagram at atmospheric pressure.
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Several important concepts emerge from studies of the equilibrium crystallization of two‐component eutectic systems such as diopside–anorthite:
1 Which minerals crystallize first from magma depends on the specifics of melt composition
2 Separation of crystals from the melt generally causes melt composition to change
3 Multiple minerals can crystallize simultaneously from a magma.
This means that no standard reaction series, such as Bowen's reaction series (ssss1), can be applicable to all magma compositions because the sequence in which minerals crystallize or whether they crystallize at all is strongly dependent on magma composition, as well as on other variables. It also means that the separation of crystals from liquid during magma crystallization generally causes magma compositions to change or evolve through time. These topics are discussed in more detail in ssss1, which deals with the origin, crystallization and evolution of magmas.