Gypsum has many application. some of as below :

Drilling Fluids :
The chemical CaSO4, which occurs naturally as the mineral anhydrite. Gypsum is the dihydrate mineral form, CaSO4·2H2O. Anhydrite and gypsum (commonly called gyp) are found in the subsurface and drilling even small stringers of these minerals can upset a freshwater or seawater mud. Gyp muds, lime muds and oil muds tolerate these salts best. CaSO4 is used as a mud treatment when no pH increase is needed to remove carbonate ion contamination in freshwater and seawater muds. (Lime increases pH when added for this purpose.) Gypsum and lime treatments are often used together to keep pH in the proper range.
 

Fertililizer / Agriculture :
Calcium sulfate dihydrate or more commonly known “Gypsum” has been used as an economical fertilizer for more than 200 years Gypsum helps plants build extensive root systems to support the plants and their yields through stressful conditions.

Use in Dry Walls
Drywall is created out of gypsum powder. This powder is led towards evaporation of most of its content of water and carbon dioxide to be converted to Calcium Sulfate Hemihydrate (also known as Plaster of Paris). Plaster of Paris converts back to CalciumSulfateDihydrate when it is mixed back with water. Such slurry is transferred to space between two hard sheets of heavy paper. It is flattened and allowed to set for forming drywall. The resulting drywall is subject to further drying, cutting, finishing and packaging for sale. Dry walls made of gypsum powder are thermal resistant and fire resistant, provides sound insulation, is durable and easy to repair. Drywall can assume many finishes such as paint, texturing or wallpaper. One 4 by 8-foot drywall panel of half-inch thickness weighs around 54 pounds. Dry walls are used for ceilings and finishing of internal walls.

Other Application
Gypsum is widely used in manufacturing of cement. It acts as retarder, controlling the setting time of cement. Gypsum free from coloring matter and of high purity is used in manufacturing of white cement.
Gypsum in manufacturing of ammonium sulphate.
In the manufacturing of P.O.P., ceramics and distemper gypsum of transparent variety is used. Surgical plasters also require gypsum having purity of 90 %.
It is also used as soil conditioner for absorption of moisture and nitrogen. It is utilized for carving and statuary purposes.
Large quantity of gypsum is used in the manufacturing of , partition blocks, tiles, stucco etc.