Class : Sulfates, chromates, molybdates
    Subclass : Hydrated sulfates
    Crystal system : Orthorhombic
    Chemistry : MgSO₄ 7H₂O
    Rarity : Common

Epsomite is a primary mineral of salt deposits, thermal springs and volcanic fumaroles. Its genesis is comparable to that of mirabilite which is its sodium equivalent ; in this case it accompanies halite and many other chlorides and sulfates. Epsomite can also be of secondary origin : it is then a reaction product between sulfuric acid formed by oxidation of sulfides and the surrounding rocks, it is then associated with numerous other iron and aluminum sulphates. By (artificial) replacement of Mg with other metals, solid solutions are obtained with morenosite (nickel-bearing), and goslarite (zinc-bearing). By dehydration and loss of a water molecule, it is transformed into hexahydrite. It owes its name to its location of discovery : Epsom in England. Epsomite sometimes appears in magnificent elongated prismatic crystals with often hemihedral endings. Ordinarily, however, it constitutes efflorescences or fibrous to acicular masses, sometimes stalactites, with a silky shine. Epsomite is colorless, white to yellowish, sometimes pink or greenish. After uses in medicine in ancient times, epsomite is today confined to a wiser role as an accessory source of magnesium.

Main photo : Epsomite from Hattorf Potash Works, Phillippsthal, Hesse, Germany © David J. Eicher

A twin is known on {110} but rare.

No fake listed for this mineral species.