» For the amorphous volcanic glass see perlite. Pearlite is a two-phased, lamellar (or layered) structure composed of alternating layers of alpha-ferrite (88 wt%) and cementite (12%) that occurs in some steels and cast irons. It forms by a eutectoid reaction as austenite is slowly cooled below 727°C. The eutectoid composition of Austenite is approximately 0.8% carbon (External Link); steel with less carbon content will contain a corresponding proportion of relatively pure ferrite crystal… (More on Pearlite)