How much clay is used to make cement?

Clay is a compact, impermeable sedimentary rock that becomes plastic, malleable, and more or less thixotropic if there is water present. Its physico-chemical properties vary in accordance with its fineness of grain. Consisting basically of aluminosilicate, it is one of the raw materials from which cement and hydraulic lime are made (contents of 30 to 40%). It is found in greater or lesser quantities in marl. Clay generally has a high content of impurities such as mica, quartz, and granite. The combination of materials required to make artificial cement was discovered in 1817 by Louis Vicat who made the results of his research into the hydraulicity of lime and cement freely available to all.