Magnesium sulfates are common minerals in geological environments. Their occurrence is mostly connected with supergene processes. Some of them are also important constituents of evaporitic potassium-magnesium (K-Mg) salts deposits.
Bright spots observed by the Dawn Spacecraft in Occator Crater on the dwarf planet Ceres are most consistent with reflected light from magnesium sulfate hexahydrate.
Almost all known mineralogical forms of MgSO4 are hydrates. Epsomite is the natural analogue of "Epsom salt". Meridianiite, MgSO4·11H2O, has been observed on the surface of frozen lakes and is thought to also occur on Mars. Hexahydrite is the next lower (6) hydrate. Three next lower hydratesâ€”pentahydrite, starkeyite, and especially sanderite are rare. Kieserite is a monohydrate and is common among evaporitic deposits. Anhydrous magnesium sulfate was reported from some burning coal dumps.
The main external use is the formulation as bath salts, especially for foot baths to soothe sore feet. Such baths have been claimed to also soothe and hasten recovery of muscle pain, soreness, or injury. However, these claims have not been scientifically confirmed. The main benefit of the salt is cosmetic: it prevents the temporary skin wrinkling caused by prolonged immersion in plain water. It is also the usual component of the solution used in isolation tanks.