Continuous cooling transformation (CCT) and time–temperature transformation (TTT) diagrams were plotted for CaO–Al2O3–MgO–FeO melts, and the morphology of the primary crystals formed was determined with a confocal laser scanning microscope (CLSM). When the CaO/Al2O3 ratio is 1.0, the crystallization temperature and incubation time increase with increasing MgO content. The TTT curve at 7.5 mass% MgO has a “C” shape, which facilitates the formation of amorphous phases. However, increasing the FeO content accelerated the crystallization time and lowered the crystallization temperature. The solidified melt with an FeO content of less than 10 mass% was a combination of the C3MA2 and C5A3 phases; higher FeO content led to the formation of a secondary phase of Ca2FeAlO5 and CA following the precipitation of the C3MA2 primary phase. In addition, kinetic evaluation of the crystal growth with confocal micrographs indicated that the calculated crystal volume agreed well with the Johnson–Mehl–Avrami sigmoidal curve fit.