Question

What is the chemical formula of gypsum?

Answer 1

To find the chemical formula of gypsum one must know the chemical name of the compound. Once that is known the atoms that together constitute it and satisfying the valency one can write down the chemical formula of the given compound.

Complete answer:
As stated earlier one must know the chemical name of the gypsum mineral. It is made up of two molecules of water, $Calcium$ , $Sulphate$ and $Oxygen$ , where the $Sulphate$ is attached to $Oxygen$ . It is a very common $Sulphate$ . The chemical name of gypsum is $Calcium{\text{ }}Sulphate{\text{ }}dihydrate$ . It is represented by the formula $CaS{O_4}.2{H_2}O$ .
The structure of Gypsum consists of layers of $Calcium$ and $Sulphate$ ions tightly bound together. These layers are bonded by the sheets of anion water molecules via weaker hydrogen bonding which gives the crystal perfect cleavage along the sheets.
Gypsum is a soft $Sulphate$ mineral. It is widely used as a fertilizer and is the main constituent in many forms of plaster, blackboard chalk and drywall. A massive fine grained white or lightly tinted variety of gypsum called alabaster has been used for sculpture by many cultures including Egypt, Rome etc. Gypsum also crystallizes as translucent crystals of selenite. It forms as an evaporite mineral and as a hydration product of anhydrite.
Gypsum is moderately soluble in water and as we increase the temperature it becomes less soluble. On heating in air it loses water and converts first to $calcium{\text{ }}sulphate{\text{ }}hemihydrate$ and then to $calcium{\text{ }}sulphate$ .

Note:
There are synthetic gypsum as well which are recovered via flue-gas desulfurization at some coal-fired power plants. It can be used interchangeably with natural gypsum in some applications. The formation of gypsum starts as tiny crystals of a mineral called bassanite.