Incongruent melting
Incongruent melting occurs when a solid substance does not melt uniformly. During melting a new solid forms. For example, melting of orthoclase produces leucite in addition to a melt. The melt produced is rich in silica so that the proportions of leucite and melt created can be recombined to yield the bulk composition of the starting feldspar. Another mineral that melts incongruently is enstatite, which produces forsterite in addition to a melt. Enstatite melts congruently between pressures of 2.5 and 5.5 kilobars.
