Which one of the following materials contains calcium?

Gypsum is hydrated calcium sulphate, CaSO₄·2H₂O, so calcium is a basic constituent of the mineral. The question tests whether you know the chemical composition of common industrial minerals.

• China clay (A): chiefly kaolinite, Al₂Si₂O₅(OH)₄. It contains aluminium and silicon, with no calcium.
• Corundum (B): aluminium oxide, Al₂O₃. It is the second hardest natural mineral after diamond, which is why it is used as an abrasive, but it has no calcium.
• Talc (D): hydrated magnesium silicate, Mg₃Si₄O₁₀(OH)₂. The metal here is magnesium, not calcium.

Core concept: mineral composition of industrially important minerals. Gypsum is mined mainly in Rajasthan and Tamil Nadu and is used in cement as a setting regulator and in plaster of Paris. For Mains, it links to mineral-based industries and the cement value chain.

Trap: aspirants pick China clay or talc because they sound like familiar, soft earth materials and assume clays carry calcium. Memorise the formulas of common minerals instead of guessing from their texture.