Incongruent melting occurs when a solid substance being partially melted does not melt uniformly, so that the chemical composition of neither the resulting liquid nor the resulting solid is the same as that of the original solid.
The melt produced is richer in silica (SiO2).
The proportions of leucite and melt formed can be recombined to yield the bulk composition of the starting feldspar.
Enstatite melts congruently at higher pressures between 2.5 and 5.5 kilobars.
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