Epsomite

Epsomite
File:Epsomita 01.jpg Epsomite formation from a Calatayud, Spain cave
General
Category	Sulfate mineral
Formula	MgSO4·7H2O
IMA symbol	Esm
Strunz classification	7.CB.40
Dana classification	29.6.11.1
Crystal system	Orthorhombic
Crystal class	Disphenoidal (222) H-M symbol: (2 2 2)
Space group	P2₁2₁2₁
Unit cell	a = 11.86, b = 11.99 c = 6.858 [Å]; Z = 4
Identification
Color	White, grey, colorless, or pink, greenish
Crystal habit	Acicular to fibrous encrustations
Twinning	Rarely observed on {110}
Cleavage	{010} perfect {101} distinct
Fracture	Conchoidal
Mohs scale hardness	2
Luster	Vitreous, silky when fibrous
Diaphaneity	Transparent to translucent
Specific gravity	1.67–1.68
Optical properties	Biaxial (−)
Refractive index	nα = 1.433 nβ = 1.455 nγ = 1.461
Birefringence	δ = 0.028
2V angle	Measured: 52°
Solubility	In water
Alters to	Dehydrates in dry air
References

Epsomite, Epsom salt, or magnesium sulfate heptahydrate, is a hydrous magnesium sulfate mineral with formula MgSO₄·7H₂O.

Physical properties

Epsomite crystallizes in the orthorhombic 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 around 2.0~2.5, and it has a low specific gravity of 1.67.

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 structure.

The epsomite group includes solid solution series with morenosite (NiSO
₄·7 H
₂O) and goslarite (ZnSO
₄·7 H
₂O).

Etymology

It was first systematically described in 1806 for an occurrence near Epsom, Surrey, England, 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 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. It occurs in association with melanterite, gypsum, halotrichite, pickeringite, alunogen, rozenite, and mirabilite.

Naturally occurring epsomite in caverns can potentially produce particulates 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 (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 magnesium (for example Epsom salt baths) is very limited. The trade organization 'Epsom Salt Council' recommends bathing 2 or 3 times/week, using 500–600 g (18–21 oz) Epsom salts each time.

Gallery

File:Epsomite crystal structure.png

The crystal structure of epsomite.

File:Epsomite cave cotton 2.png

Scanning electron micrograph of epsomite fibers magnified 300 times, from a sample found on a wall of a former limestone quarry cavern in Ohio.

See also

• Magnesium sulfate