A reversible reaction that involves the conversion of two liquid phases, l' and l'', into a solid phase α on cooling: \[\text{l}^{'}+\text{l}^{''}\rightleftharpoons \unicode[Times]{x3B1} \] The maximum temperature at which this reaction can occur is the congruent melting point of the solid phase. Example: The conversion of co-existing K-rich and Zn-rich phases in the K-Zn system to form an intermediate solid phase KZn₁₃.