Formula: Mg(SO4).7H2O
Hydrated normal sulphate, epsomite group, forms a series with morenosite and with goslarite. Epitaxial on muscovite, morenosite and goslarite (Mindat).
Specific gravity: 1.68
Hardness: 2 to 2½
Streak: White
Colour: White, sometimes greenish, reddish, yellowish
Solubility: Effloresces in dry air. Very soluble in water.
Common impurities: Ni,Fe,Co,Mn,Zn

Evaporite deposits
Hot spring deposits
Cave deposits

Epsomite is typically found growing as efflorescences in sheltered spots on outcrops of dolostone or limestone; it is often found growing on the walls of caves and in salt lake deposits, and also on the walls of coal and metal mines, including on wooden supports and abandoned equipment. Epsomite is likely to occur in the Martian soils and on the satellites of Jupiter (Mindat). It is a product of evaporation at mineral springs and saline lakes, a hydration product of kieserite and langbeinite, and rarely a fumarolic sublimate. In efflorescences it is associated with melanterite, gypsum, halotrichite, pickeringite, alunogen and rozenite; in lacustrine evaporites it is associated with mirabilite (HOM).


In the evaporite basins in the Mallee district, Murray basin, south-eastern Australia, crude crystals of epsomite form with halite and gypsum in the black mud under the salt crust of the halite salt lakes (AJM 10.1.17).

At Llallagua, Rafael Bustillo, Potosí, Bolivia, epsomite fibres occur on melanterite and chalcanthite stalactities (Minrec 37.2.133).

At Gordon's Quarry, Kaukapakapa, Auckland Region, North Island, New Zealand, nickel-bearing epsomite was found as efflorescent patches on freshly broken surfaces of serpentinite where the serpentinite encloses scattered grains of pentlandite-bearing pyrrhotite. Tn the same quarry nickel-free epsomite was also observed at other points on the serpentinite surface. The pyrrhotite has been oxidised to give ferric sulfate and sulfuric acid; the sulfuric acid has apparently reacted with the serpentinite and with the pentlandite in the pyrrhotite giving sulphates including epsomite (AM 32.553-560).

At the Brownley Hill mine, Nenthead, Alston Moor, Eden, Cumbria, England, UK, epsomite occurs as hairlike crystals to 10 cm, alone or with gypsum, as post-mining efflorescences on the mine walls (Minrec 31.3.245).

The type locality is Epsom Spa, Epsom and Ewell, Surrey, England, UK.

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