syntectic reaction

A reversible reaction that involves the conversion of two liquid phases, $l '$ and $l ''$ , into a solid phase α on cooling:

$l ' + l '' ⇌ α$

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.

Source:

PAC, 1994, 66, 577 (Definitions of terms relating to phase transitions of the solid state (IUPAC Recommendations 1994)) on page 592