Chemistry:Incongruent melting

Short description: When a solid substance does not melt uniformly

Incongruent melting occurs when a solid substance does not melt uniformly, so that the chemical composition of the resulting liquid is not the same as that of the original solid. During incongruent melting a new solid of different composition forms. For example, melting of orthoclase (KAlSi₃O₈) produces leucite (KAlSi₂O₆) in addition to a melt. 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. Another mineral that can melt incongruently is enstatite (Mg₂Si₂O₆), which produces forsterite (Mg₂SiO₄) in addition to a melt richer in SiO₂ when melting at low pressure. Enstatite melts congruently at higher pressures between 2.5 and 5.5 kilobars.

See also

• Congruent melting
• Incongruent transition
• Phase diagram

References

• Incongruent melting from Eric Weisstein's World of Physics