Gypsum
Gypsum (CaSO4.2H2O) is a common sulfate mineral made of calcium sulfate. Gypsum has been used as a building material for a long time, possibly since the neolithic. Today, it is used in drywall, and as an ingredient of plaster of Paris. It can also be used as a fertilizer. It is softer than most minerals, with a value of 2 on the Mohs scale of mineral hardness. This mineral can be, somewhat, scratched with your fingernail. A fingernail, with a value of 2.5 on the Mohs scale of mineral hardness is in fact higher than the mineral shown above. It is an ingredient of Portland cement. Gypsum was used in ancient Egypt and Mesopotamia by sculptors. It is also used in making surgical and orthopedic cast molds.
