Calcium sulfate
Hydrated Calcium sulfate, or gypsum, is a chemical compound with the general formula of CaSO4 + H2O was found on Mars in 2011 by the Opportunity rover. A surface vein was identified on the Martian surface.
The main use of Calcium sulfate, when adequately treated with heat (dehydrated), is plaster of Paris, or stucco. This is used as a finishing compound, or as an element of drywall construction. Drywall construction can provide fire safety for structural elements.
Sulfates rather than carbonates
Geologists expected to find large amounts of carbonates on Mars, but surprisingly they seem to be fairly rare. The current theory is that Martian water was acidic and sulfates such as calcium sulphate (CaSO4) were easier to form. If this is the case, we may discover, very large amounts of CaSO4 on Mars.