- Binary eutectic diagrams summarize experimental data on the melting and crystallization of idealized, two-component igneous rocks.
- Liquidus curves on these diagram, which are saturation curves for individual minerals, identify the temperature above which a rock is completely melted for each bulk composition.
- Liquidus curves for two minerals may meet at a eutectic point, which gives the temperature and chemical composition of the first liquid formed when a rock made of the two minerals is heated.
- Liquidus curves for two minerals may meet at a peritectic point, which gives the temperature and chemical composition of the liquid formed when one of the two minerals melts incongruently to produce a liquid and the other mineral.
- Minerals that melt by themselves upon heating to a liquid of the same composition melt congurently.
- Minerals that melt by themselves to a liquid of a different composition and a new mineral melt incongruently.
- Magmas whose composition passes through a peritectic point upon cooling may coat or armour grains of an early-formed mineral, isolating and preserving them with a reaction rim that effectively changes the chemical composition of the remaining liquid.
4.5 Summary
