Magnesium sulfate or magnesium sulphate is a chemical compound, a salt with the formula MgSO4, consisting of magnesium cations Mg2+ (20.19% by mass) and sulfate anions SO 2− 4 . It is a white crystalline solid, soluble in water but not in ethanol. Magnesium sulfate is usually encountered in the form of a hydrate MgSO4·nH2O, for various values of n between 1 and 11. The most common is the heptahydrate MgSO4·7H2O, [1] known as Epsom salt, which is a household chemical with many traditional uses, including bath salts.[2] The main use of magnesium sulfate is in agriculture, to correct soils deficient in magnesium (an essential plant nutrient because of the role of magnesium in chlorophyll and photosynthesis). The monohydrate is favored for this use; by the mid 1970s, its production was 2.3 million tons per year.[3] The anhydrous form and several hydrates occur in nature as minerals, and the salt is a significant component of the water from some springs. Hydrates Magnesium sulfate can crystallize as several hydrates, including: Anhydrous, MgSO4; unstable in nature, hydrates to form epsomite.[4] Monohydrate, MgSO4·H2O; kieserite, monoclinic.[5] Monohydrate, MgSO4·H2O; triclinic.[6] MgSO4·1.25H2O or 4MgSO4·5H2O.[7] Dihydrate, MgSO4·2H2O; orthorhombic. MgSO4·2.5H2O or 2MgSO4·5H2O.[7] Trihydrate, MgSO4·3H2O.[7] Tetrahydrate, MgSO4·4H2O; starkeyite, monoclinic.[8] Pentahydrate, MgSO4·5H2O; pentahydrite, triclinic.[5] Hexahydrate, MgSO4·6H2O; hexahydrite, monoclinic. Heptahydrate, MgSO4·7H2O ("Epsom salt"); epsomite, orthorhombic.[5] Enneahydrate, MgSO4·9H2O, monoclinic.[9] Decahydrate, MgSO4·10H2O.[8] Undecahydrate, MgSO4·11H2O; meridianiite, triclinic.[8] As of 2017, the existence of the decahydrate apparently has not been confirmed.[9] All the hydrates lose water upon heating. Above 320 °C, only the anhydrous form is stable. It decomposes without melting at 1124 °C into magnesium oxide (MgO) and sulfur trioxide (SO3). Heptahydrate