The normal form is as massive encrustations, while acicular or fibrous crystals are rarely found.

[3][clarification needed] It was first systematically described in 1806 for an occurrence near Epsom, Surrey, England, after which it was named.

[6] 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 such as those found in certain bodies of salt water.

[5][7] It occurs in association with melanterite, gypsum, halotrichite, pickeringite, alunogen, rozenite, and mirabilite.

[4] Naturally occurring epsomite in caverns can potentially produce particulates of inhalable size, and may contain significant amounts of toxic impurities.