Cement Clinkers are formed by the heat processing of cement elements in a kiln. Limestone, clay, bauxite, and iron ore sand in specific proportions are heated in a rotating kiln at 2,770 Fahrenheit (1,400 Celsius) until they begin to form cinder lumps, which are also known as cement clinkers. These are usually ground with gypsum to produce the fine powder later mixed with liquid to produce cement. Cement is heavily relied upon to produce mortar, grouts, and concrete, and cement clinkers are the first stage, post firing, in making cement. clinker iran