The phase equilibrium data on an organic analog of a metal-nonmetal system involving 4-bromochlorobenzene-succinonitrile show the formation of a eutectic and a monotectic with a large miscibility gap containing 0.96 and 0.03 mole fractions of succinonitrile, respectively, with the consolute temperature of 180.0 degrees C. The heat of mixing, entropy of fusion, roughness parameter, interfacial energy and excess thermodynamic functions were calculated from the enthalpy of fusion values, determined by the DSC method using TA Instruments DSC-2010. The effects of solid-liquid interfacial energy on morphological change of monotectic have also been discussed. The microstructures of monotectic and eutectic show the lamellar growth characteristic. (C) 2009 Elsevier B.V. All rights reserved.