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solvus

707030solvusexsolves7030883exsolutionperthite80antiperthite

ssss1 Phase diagram for the system nepheline–silica with the intermediate compound albite, at atmospheric pressure.

nepheline–silica phase diagramintermediate compoundsilica (SiO2)nepheline (NaAlSiO4)42albite (NaAlSi3O8)222

silica saturationoversaturated with respect to silicaundersaturated with respect to silicasaturated with respect to silica

The nepheline–silica phase diagram shows some similarity to the diopside–anorthite phase diagram. The most significant difference is the presence of two eutectic points where troughs in the liquidus intersect the solidus. For many purposes, this diagram may be interpreted as two side‐by‐side eutectic diagrams: one diagram for undersaturated compositions (less than two‐thirds silica component), with a eutectic point at 1070 °C and ~62% silica component, and a second diagram for oversaturated compositions (over two‐thirds silica component), with a eutectic point at 1060 °C and ~77% silica component. A brief discussion of the crystallization and melting behaviors for these two compositional ranges follows.