Portland cement is finely ground
a) Calcium aluminates and silicates of varying compositions
b) Calcium aluminates and caustic soda
c) Calcium aluminates and sodium silicates of varying compositions
d) Calcium silicates and gypsum of fixed composition
The major raw material for the clinker-making is usually limestone (CaCO3) mixed with a second material containing clay as source of alumino-silicate. Normally, an impure limestone which contains clay or SiO2 is used. The CaCO3 content of these limestones can be as low as 80%. Secondary raw materials (materials in the raw mix other than limestone) depend on the purity of the limestone. Some of the materials used are clay, shale, sand, iron ore, bauxite, fly ash, and slag. When a cement kiln is fired by coal, the ash of the coal acts as a secondary raw material.
A is the answer.