Cement is made from a mixture of 80 percent limestone and 20 percent clay. These are crushed and ground to provide the "raw meal”, a pale, flour-like powder. Heated to around 1450° C (2642° F) in rotating kilns, the “meal” undergoes complex chemical changes and is transformed into clinker. Fine-grinding the clinker together with a small quantity of gypsum produces cement. Adding other constituents at this stage produces cements for specialized uses.