Gypsum

The very soft sulphate mineral, gypsum, is widely mined throughout the world. It is one of the main constituents of plaster and is a wonderful soil conditioner and fertiliser found to be very valuable in the agricultural industry. Gypsum, in the form of alabaster, is very finely grained of a white or slightly tinted hue that is particularly popular among sculptors going back to ancient Egypt and medieval England.

The Many Uses of Gypsum

Gypsum is found to be commonplace throughout most countries of the world with global production exceeding 100 million tonnes annually. Its most common uses include the following:

Mushroom growing where it prevents grains clumping together
Widely used in China as a medicine known as “Shi-Gao”
Impression plaster in the dentistry industry
As hair products, shampoo and foot creams
A main ingredient in the making of mead
Monitoring of soil and water moisture tension
Used in cement to prevent flash setting
A main component in mineral yeast food
A dough conditioner when baking that reduces sticking and a source of dietary calcium
Homebrewing use as a water hardener
A clay tennis court surface binder
A fertiliser and soil conditioner
An ingredient in the plaster used in the making of surgical splints, modelling clay and casting moulds
As plasterboard, or gypsum board, in the construction industry as walls and ceilings

Gypsum was also used in the form of alabaster for sculpture before the advent of steel when its relative softness facilitated its carving potential. It was also substituted for wood during the bronze age when wood became scarce. Many Asian cultures also used gypsum as a source of dietary calcium in the form of a soy bean curd known as a tofu.

Heated Gypsum Becomes Plaster of Paris

Gypsum has been found useful around the world because of the relative ease it has in losing and regaining its water of crystallisation, as when heated to between 300 and 350 degrees Celsius it loses 75 percent of its water content to become Plaster of Paris. In this form, and when water is added, it can be spread, moulded or cast before it once again regains its water of crystallisation and sets.

Gypsum Use in the Cement Industry

Gypsum is used in the cement industry by adding it at the rate of between two and five percent to cement clinker before it is finally ground. This slows down its setting rate when used in the making of concrete.

Gypsum in Agriculture

In the agriculture industry gypsum is used to assist farmers in cultivation and the prevention of erosion. The calcium content contained in gypsum displaces sodium that allows deeper leaching into the soil. It assists in the prevention of surface crusting, improves the soil's water storage and slows run off.

Australia's Largest Gypsum Mine is at Lake MacDonnell in South Australia

The largest gypsum mine in Australia is the Lake MacDonnell Mine in South Australia that has a resource of 500 million tonnes. It has been producing gypsum since 1919. The gypsum deposit at Lake MacDonnell is mined and left in stockpiles for several years that allows natural leaching to occur through rainwater that reduces its salt content. The Lake Macdonnell gypsum deposit covers an area of 87 square kilometres.