Calcium Sulfate, CaSO4, is a naturally occurring calcium salt available in three forms. This calcium compound is most recognized in its dihydrate form gypsum or calcium sulphate dihydrate (CaSO4∙2H2O). In its anhydrous form (CaSO4), it’s used as a desiccant (dries things out). The third form is The third form it can be found in is calcium sulphate hemihydrate (CaSO4·1/2H2O) which is known as the plaster of Paris.

Calcium Sulfate 

Gypsum and anhydrite are the biggest sources of calcium sulphate in the world. It can also be produced as a by-product of other processes. 


  • Cement manufacturing
  • Filler in paper
  • Desiccant
  • Firming agent in foods
  • Paint pigment
  • Polishing powder production
  • Animal feed additive

Calcium Sulfate Dihydrate 

This is commonly used in building materials for construction such as

  • Portland cement
  • Specialized wall plasters
  • Wallboard production
  • Cement blocks
  • Mortars
  • Soil conditioning agent

Calcium sulphate hemihydrate

This calcium compound is best known for being the plaster of Paris. It’s a fast-setting gypsum plaster made of a fine white powder. It hardens when moistened and is allowed to dry. It got its nickname from the popularity of gypsum in the city of Paris. It’s suitable as a casting mould which makes it popular in building materials and the medical profession.

Calcium Carbonate

CaCO3 is a dietary supplement used when calcium intake is too low. Adequate calcium intake is crucial in the development of strong healthy bones, muscles, heart, and nervous system. It can also be used as an antacid for relieving heartburn, indigestion, and upset stomach. It is found in rocks and shells such as eggshells, snail shells, seashells, and pearls. 

Is Calcium Sulphate Soluble in Water?

Calcium sulphate is insoluble or only partially soluble in water, depending on temperature conditions and which particular form of calcium sulphate we are talking about. Because calcium sulphate anhydrite is made from dehydrating calcium sulphate dihydrate, it is insoluble at high temperatures.

At room temperature, it will dissolve very slowly at .24g per 100 g of water as well as not absorbing moisture from the air. Finally, at temperatures below 300 degrees Celsius, soluble anhydrite will absorb water to form plaster of Paris (calcium sulphate hemihydrate)

How It’s Made

The abundant mineral gypsum naturally contains calcium sulphate. When natural gypsum is crushed and heated at temperatures between 100-125 degrees Celsius, for several hours, gypsum is converted to the hemihydrate form or anhydrous calcium sulphate, which depends on the specific reached temperature. It can also be produced as a by-product of other reactions as well as through synthetic processes. 


Anhydrous and calcium sulphate and calcium hemihydrate appear as fine white powders and have no odour. Dihydrate can take on the form of a powder as well or as white lumps. The three main forms of calcium sulphate have a wide variety of uses extending across many different fields of industry. 

If you’d like to enquire about calcium sulphate and its applications, contact us at Biz International and our team of experts would be happy to offer some recommendations.