How cement is made Raw materials. Iron oxide and gypsum make up the rest of the materials. The gypsum regulates the setting, or hardening, time of cement. The lime comes from materials such as limestone, oyster shells, and a type of clay called marl. Shale, clay, silica sand, slate, and blast-furnace slag provide the silica and alumina.
Iron oxide is supplied by iron ore, pyrite, and other materials.
Most cement plants are located near limestone quarries. They may also be near deposits of clay and other raw materials. Ships, trains, trucks, and conveyer belts haul the limestone and other raw materials to the plants. Crushing and grinding. The quarried limestone is dumped into primary crushers that can handle pieces as large as an upright piano.