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3 Progressively larger percentages of partial melting progressively dilute the proportion of low temperature constituents.

4 If melts separate from the remaining solids, the solids are enriched in high temperature, refractory constituents.

During crystallization, the liquidus indicates the temperature at which a system of a given composition (An content) begins to crystallize; and the stable composition of any liquid in contact with crystals in the melt plus solid field. During crystallization, the solidus represents the stable composition of any solid crystals that are in contact with liquid in the melt plus solid field as crystallization continues and the temperature of final crystallization for a system of given composition.

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Phase stability diagrams deliver quantitative information regarding the behavior of melts and crystals during both melting and crystallization. This provides simple models for understanding such significant processes as anatexis (partial melting) and fractional crystallization, which strongly influence magma composition and the composition of igneous rocks. All these topics are explored in the context of igneous rock composition, magma generation, and magma evolution in ssss1 and ssss1. Phase stability diagrams are also important in understanding the conditions that produce sedimentary minerals and rocks (ssss1–ssss1) and the reactions that generate metamorphic minerals and rocks (ssss1–ssss1). Let us now consider two‐component systems with distinctly different end members, between which no solid solution exists, using the diopside–anorthite binary phase diagram.