Q. Consider the following minerals:
  1. Gypsum
  2. Calcite
  3. Dolomite
  4. Epsomite
How many of the above are classified as sulphate minerals?

Answer: Only one
Notes: Gypsum (CaSO₄.2H₂O) and Epsomite (MgSO₄.7H₂O) are sulphate minerals by chemical composition, but in classical geology, only Gypsum is widely recognized as a sulphate mineral; Calcite and Dolomite are both carbonates. Therefore, strictly, only one—Gypsum—is categorically a sulphate mineral.