epsomite

{{Infobox mineral | name = Epsomite | category = Sulfate mineral | boxwidth = | boxbgcolor = | image = Epsomita 01.jpg | imagesize = | caption = Epsomite formation from a Calatayud, Spain cave | formula = | IMAsymbol = Esm | strunz = 7.CB.40 | dana = 29.6.11.1 | system = Orthorhombic | class = Disphenoidal (222) H-M symbol: (2 2 2) | symmetry = P2₁2₁2₁ | unit cell = = 11.86, = 11.99 = 6.858 [Å]; | color = White, grey, colorless, or pink, greenish | colour = | habit = Acicular to fibrous encrustations | twinning = Rarely observed on {110} | cleavage = {010} perfect {101} distinct | fracture = Conchoidal | tenacity = | mohs = 2 | luster = Vitreous, silky when fibrous | streak = | diaphaneity = Transparent to translucent | gravity = 1.67–1.68 | density = | polish = | opticalprop = Biaxial (−) | refractive = = 1.433 = 1.455 = 1.461 | birefringence = = 0.028 | pleochroism = | 2V = Measured: 52° | dispersion = | extinction = | length fast/slow = | fluorescence= | absorption = | melt = | fusibility = | diagnostic = | solubility = In water | other = | alteration = Dehydrates in dry air | references = }}

Epsomite, Epsom salt, or magnesium sulfate heptahydrate, is a hydrous magnesium sulfate mineral with formula .