The structure and orientation of graphite platelets in graphite spherulites (GS) in cast irons modified by either cerium or magnesium plus cerium were investigated by TEM and micro-diffraction. The platelets have a rhombohedral structure with their [001] directions nearly parallel to the radius of the GS, but each platelet is twisted about 2-degrees over a 1 mum length. Randomly orientated graphite is located in the interplatelet areas, in which most of the graphite has a hexagonal structure rather than rhombohedral structure. Based on the crystallographic characterization of the graphite and the cerium and magnesium elemental distribution in the GS, the model for the growth of GS as originally proposed by Double and Hellawell is re-examined.