Epsomite, Epsom salt, or magnesium sulfate heptahydrate, is a hydrous

magnesium sulfate Magnesium sulfate or magnesium sulphate is a chemical compound, a salt with the formula , consisting of magnesium cations (20.19% by mass) and sulfate anions . It is a white crystalline solid, soluble in water but not in ethanol. Magnesi ...

mineral with formula .

Physical properties

Epsomite crystallizes in the

orthorhombic In crystallography, the orthorhombic crystal system is one of the 7 crystal systems. Orthorhombic Lattice (group), lattices result from stretching a cubic crystal system, cubic lattice along two of its orthogonal pairs by two different factors, res ...

system. The normal form is as massive encrustations, while acicular or fibrous crystals are rarely found. It is colorless to white with tints of yellow, green and pink. It is a soft mineral with variable

Mohs hardness The Mohs scale ( ) of mineral hardness is a qualitative ordinal scale, from 1 to 10, characterizing scratch resistance of mineral In geology and mineralogy, a mineral or mineral species is, broadly speaking, a solid substance with a fair ...

around 2.0~2.5, and it has a low

specific gravity Relative density, also called specific gravity, is a dimensionless quantity defined as the ratio of the density (mass of a unit volume) of a substance to the density of a given reference material. Specific gravity for solids and liquids is nea ...

It is readily soluble in water, and absorbs water from the air. It converts to hexahydrate with the loss of one water molecule and a switch to

monoclinic In crystallography, the monoclinic crystal system is one of the seven crystal systems. A crystal system is described by three Vector (geometric), vectors. In the monoclinic system, the crystal is described by vectors of unequal lengths, as in t ...

structure. The epsomite group includes

solid solution A solid solution, a term popularly used for metals, is a homogeneous mixture of two compounds in solid state and having a single crystal structure. Many examples can be found in metallurgy, geology, and solid-state chemistry. The word "solutio ...

series with morenosite (·) and

goslarite Goslarite is a water of crystallization, hydrated zinc sulfate mineral () which was first found in the Rammelsberg mine, Goslar, Harz, Germany. It was described in 1847. Goslarite belongs to the epsomite group which also includes epsomite () and ...

(·).

Etymology

It was first systematically described in 1806 for an occurrence near

Epsom Epsom is a town in the borough of Epsom and Ewell in Surrey, England, about south of central London. The town is first recorded as ''Ebesham'' in the 10th century and its name probably derives from that of a Anglo-Saxon settlement of Britain ...

Surrey Surrey () is a Ceremonial counties of England, ceremonial county in South East England. It is bordered by Greater London to the northeast, Kent to the east, East Sussex, East and West Sussex to the south, and Hampshire and Berkshire to the wes ...

England England is a Countries of the United Kingdom, country that is part of the United Kingdom. It is located on the island of Great Britain, of which it covers about 62%, and List of islands of England, more than 100 smaller adjacent islands. It ...

, after which it was named. It has been also referred to as "cave cotton" when in its fibrous form.

Occurrence

Epsomite forms as encrustations or

efflorescence In chemistry, efflorescence (Derived from the Latin verb 'efflorescere' roughly meaning 'to flower') is the migration of a salt to the surface of a porous material, where it forms a coating. The essential process involves the dissolving of an i ...

s on

limestone Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...

cavern walls and mine timbers and walls, rarely as

volcanic A volcano is commonly defined as a vent or fissure in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface. On Earth, volcanoes are most often fo ...

fumarole deposits, and as rare beds in

evaporite An evaporite () is a water- soluble sedimentary mineral deposit that results from concentration and crystallization by evaporation from an aqueous solution. There are two types of evaporite deposits: marine, which can also be described as oce ...

layers such as those found in certain bodies of salt water. It occurs in association with

melanterite Melanterite is a mineral form of hydrous iron(II) sulfate: FeSO4·7H2O. It is the iron analogue of the copper sulfate chalcanthite. It alters to siderotil by Dehydration, loss of water. It is a secondary sulfate mineral which forms from the oxida ...

gypsum Gypsum is a soft sulfate mineral composed of calcium sulfate Hydrate, dihydrate, with the chemical formula . It is widely mined and is used as a fertilizer and as the main constituent in many forms of plaster, drywall and blackboard or sidewalk ...

, halotrichite, pickeringite, alunogen, rozenite, and

mirabilite Mirabilite, also known as Glauber's salt, is a hydrous sodium sulfate mineral with the chemical formula Na2SO4·10H2O. It is a vitreous, colorless to white monoclinic mineral that forms as an evaporite from sodium sulfate-bearing brines. It is ...

. Naturally occurring epsomite in caverns can potentially produce

particulates Particulate matter (PM) or particulates are microscopic particles of solid or liquid matter suspension (chemistry), suspended in the atmosphere of Earth, air. An ''aerosol'' is a mixture of particulates and air, as opposed to the particulate ...

of inhalable size, and may contain significant amounts of toxic impurities.

Uses

Epsom salt is commonly sold as the main ingredient in bath salt, with additives such as

glycerin Glycerol () is a simple triol compound. It is a colorless, odorless, sweet-tasting, viscous liquid. The glycerol backbone is found in lipids known as glycerides. It is also widely used as a sweetener in the food industry and as a humectant in pha ...

(used as a humectant) and fragrances. The purpose of bath salts is mostly to make the bathing experience more enjoyable and serve as a vehicle for cosmetics, though they are said to improve cleaning and aid in exfoliation. Research on

topical A topical medication is a medication that is applied to a particular place on or in the body. Most often topical medication means application to body surfaces such as the skin or mucous membranes to treat ailments via a large range of classes ...

magnesium (for example Epsom salt baths) is very limited. The

trade organization A trade association, also known as an industry trade group, business association, sector association or industry body, is an organization founded and funded by businesses that operate in a specific Industry (economics), industry. Through collabor ...

'Epsom Salt Council' recommends bathing 2 or 3 times/week, using Epsom salts each time.

Gallery

References