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Epsomite
Chemical Formula	MgSO4·7H2O
Species	Sulfates
Crystal System	Orthorhombic
Mohs Scale	2
Specific Gravity	1.67-1.68
Color	White, grey, colorless, or pink, greenish
Streak	White
Luster	Vitreous, Silky, Earthy
Refractive Index	n = 1.433 n = 1.455 n = 1.461
Diaphaneity	Transparent, Translucent
Cleavage	PerfectPerfect on , distinct on .
Fracture	Conchoidal
Crystal Habit：Acicular to fibrous encrustations
Geological Setting：Typically found growing as efflorescences in sheltered spots on outcrops of dolomitic or calcerous rocks; often found growing on the walls of caves and in salt lake deposits; also often found growing on the walls of coal and metal mines, including on wooden supports and abandoned equipment.

Epsomite crystallizes in the orthorhombic system as rarely found acicular or fibrous crystals, the normal form is as massive encrustations. It is colorless to white with tints of yellow, green and pink. The Mohs hardness is 2 to 2.5 and it has a low specific gravity of 1.67.

Epsomite is the same as the household chemical, Epsom salt, and is readily soluble in water. It absorbs water from the air and converts to hexahydrate with the loss of one water molecule and a switch to monoclinic structure.

Discovery and occurrence

Epsomite forms as encrustations or efflorescences on limestone cavern walls and mine timbers and walls, rarely as volcanic fumarole deposits, and as rare beds in evaporite layers. It was first systematically described in 1806 for an occurrence near Epsom, Surrey, England, after which it was named. It occurs in association with melanterite, gypsum, halotrichite, pickeringite, alunogen, rozenite and mirabilite.

Related minerals

The epsomite group includes solid solution series with morenosite (ZnSO₄·7H₂O) and goslarite (ZnSO₄·7H₂O)

Kieserite (MgSO₄·H₂O) is a less hydrated magnesium sulfate.