Which material is specifically cited as a natural rock used to produce cement?

• A. Clay
• B. Sand
• C. Limestone
• D. Iron ore

Answer: (C)

The material most often cited as the natural rock used to produce cement is limestone. Limestone is a sedimentary rock rich in calcium carbonate (CaCO3). In cement production, it is quarried and heated in kilns to drive off carbon dioxide, forming lime (CaO). That lime then reacts with silica, alumina, and other components to create the clinker that becomes cement. Limestone’s abundance and chemical composition make it the classic raw material for cement.

Clay, while used in cement mixes to provide silica and alumina, is not the primary natural rock highlighted for cement production. Sand is mainly a source of silica for specific blends or as aggregate, not the main cement precursor. Iron ore is not used for making ordinary cement.