Magnesium sulphate is an inorganic salt, with the chemical formula MgSO4. It occurs in two forms, monohydrate and heptahydrate. The heptahydrate form is MgSO4.7H2O and is commonly called as Epsom salt. The monohydrate is MgSO4.H2O and is present in the form of a mineral called kieserite.
Magnesium sulphate is often obtained from natural sources such as minerals in geological environments. They occur by the supergene process, that is, their enrichment occurs relatively near the surface. Magnesium sulphate is an important constituent of evaporitic potassium-magnesium salts deposits. Magnesium sulphate heptahydrate occurs naturally as the mineral epsomite. Another mineral called alpersite contains copper and the heptahydrate form of magnesium sulphate.
Epsom salt is a common pharmaceutical preparation of magnesium and is used both externally and internally. Epsom salt is given orally as a saline laxative or osmotic purgative. It is also the main preparation of intravenous magnesium. It is also used in the replacement therapy for hypomagnesemia, used as an antiarrhythmic agent in cardiac arrest, a bronchodilator in severe exacerbations of asthma, it is given as a first aid for barium chloride poisoning.
Magnesium sulphate is used in bath salts and to prepare foot baths to soothe sore feet. The addition of Epsom salt increases the ionic strength and prevents temporary skin wrinkling. It also gets absorbed into the skin and reduces inflammation. It is also used in floatation therapy where high concentration of Epsom salt raises the specific gravity of the bath water and makes the body buoyant.
It is used to maintain the magnesium concentration in marine aquaria which consists of large quantities of stony corals, in order to stabilize the calcium ions depleted by the calcification process.