A very common mineral, hydrated calcium sulfate, CaSO4⋅2H2O, occurs in crystals and in masses, soft enough to be scratched by the fingernail: used to make plaster of Paris, as an ornamental material, as a fertilizer, etc. Gypsum is that the name given to a mineral categorised as salt mineral, and its statement is salt dihydrate, CaSO4⋅ 2H2O.However, a broader definition includes all the atomic number 20 sulfates, together with salt hemihydrate, CaSO4⋅ 0.5H2O, that is understood as plaster or plaster of Paris (POP).