| Epsomite | |
|---|---|
 | |
| General | |
| Category | Sulfate mineral |
| Formula | MgSO4·7H2O |
| IMA symbol | Esm[1] |
| 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 = 1.433nβ = 1.455nγ = 1.461 |
| Birefringence | δ = 0.028 |
| 2V angle | Measured: 52° |
| Solubility | In water |
| Alters to | Dehydrates in dry air |
| References | [2][3][4] |
Epsomite,Epsom salt, ormagnesium sulfate heptahydrate, is ahydrousmagnesium sulfate mineral with formulaMgSO4·7H2O.
Epsomite crystallizes in theorthorhombic system. The normal form is as massive encrustations, whileacicular or fibrous crystals are rarely found. It is colorless to white with tints of yellow, green and pink. It is a soft mineral with variableMohs hardness around 2.0~2.5, and it has a lowspecific gravity of 1.67.[5]
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 tomonoclinic structure.[5]
The epsomite group includessolid solution series withmorenosite (NiSO
4·7 H
2O) andgoslarite (ZnSO
4·7 H
2O).[3][clarification needed]
It was first systematically described in 1806 for an occurrence nearEpsom,Surrey,England, after which it was named.[5] It has been also referred to as "cave cotton" when in its fibrous form.[6]
Epsomite forms asencrustations orefflorescences onlimestone cavern walls and mine timbers and walls, rarely asvolcanicfumarole deposits, and as rare beds inevaporite layers such as those found in certain bodies of salt water.[5][7] It occurs in association withmelanterite,gypsum,halotrichite,pickeringite,alunogen,rozenite, andmirabilite.[4]
Naturally occurring epsomite in caverns can potentially produceparticulates of inhalable size, and may contain significant amounts of toxic impurities.[6][8]
Epsom salt is commonly sold as the main ingredient inbath salt, with additives such asglycerin (used as ahumectant) 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.[9]
Research ontopical magnesium (for example Epsom salt baths) is very limited.[10] Thetrade organization 'Epsom Salt Council' recommends bathing 2 or 3 times/week, using 500–600 g (18–21 oz) Epsom salts each time.[11]
