# Epsomite

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Sulfate mineral

Epsomite Epsomite formation from a Calatayud, Spain cave 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 = 1.433 nβ = 1.455 nγ = 1.461 Birefringence δ = 0.028 2V angle Measured: 52° Solubility In water Alters to Dehydrates in dry air References [2][3][4]

**Epsomite**, **Epsom salt**, or **magnesium sulfate heptahydrate**, is a [hydrous](/source/Hydrous) [magnesium sulfate](/source/Magnesium_sulfate) mineral with formula MgSO4·7H2O.

## Physical properties

Epsomite crystallizes in the [orthorhombic](/source/Orthorhombic) system. The normal form is as massive encrustations, while [acicular](/source/Acicular_(crystal_habit)) 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](/source/Mohs_hardness) around 2.0~2.5, and it has a low [specific gravity](/source/Specific_gravity) of 1.67.[5]

It is readily [soluble](/source/Solubility) in water, and absorbs water from the air. It converts to hexahydrate with the loss of one water molecule and a switch to [monoclinic](/source/Monoclinic) structure.[5]

The epsomite group forms a [solid solution](/source/Solid_solution) series with [morenosite](https://en.wikipedia.org/w/index.php?title=Morenosite&action=edit&redlink=1) (NiSO 4·7 H 2O) and [goslarite](/source/Goslarite) (ZnSO 4·7 H 2O). This series' members bear the same structure as either the [nickel](/source/Nickel), [zinc](/source/Zinc), or [magnesium](/source/Magnesium) cations occupying similar positions in the lattice. Intermediate compositions containing more than one of these elements are also known.[3]

## Etymology

In 1618, a well was dug by a local farmer on [Epsom](/source/Epsom) common, half a mile west of Epsom, [Surrey](/source/Surrey), [England](/source/England), after his cattle refused to drink from surface water in the area. The well water became known and used externally as a treatment for skin diseases and other complaints, and both the well and its water were soon named for Epsom. By the mid-17th century Epsom Water had become popular as far away as continental European countries. To maintain supplies of the water, a second well was dug near the centre of the village, which had become widely known as Epsom [Spa](/source/Spa). In 1695 Dr. Nehemiah Grew published his study on the water's composition, establishing Epsom salts as a medical remedy.[6] It was later systematically described in 1806.[5] It has been also referred to as "cave cotton" when in its fibrous form.[7]

## Occurrence

Epsomite forms as [encrustations](https://en.wikipedia.org/w/index.php?title=Encrustation&action=edit&redlink=1) or [efflorescences](/source/Efflorescence) on [limestone](/source/Limestone) cavern walls and mine timbers and walls, rarely as [volcanic](/source/Volcanic) [fumarole](/source/Fumarole) deposits, and as rare beds in [evaporite](/source/Evaporite) layers such as those found in certain bodies of salt water.[5][8] It occurs in association with [melanterite](/source/Melanterite), [gypsum](/source/Gypsum), [halotrichite](/source/Halotrichite), [pickeringite](/source/Pickeringite), [alunogen](/source/Alunogen), [rozenite](/source/Rozenite), and [mirabilite](/source/Mirabilite).[4]

Naturally occurring epsomite in caverns can potentially produce [particulates](/source/Particulates) of inhalable size, and may contain significant amounts of toxic impurities.[7][9]

## Uses

Epsom salt is commonly sold as the main ingredient in [bath salt](/source/Bath_salts), with additives such as [glycerin](/source/Glycerin) (used as a [humectant](/source/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.[10]

Research on [topical](/source/Topical_medication) magnesium (for example Epsom salt baths) is very limited.[11] The [trade organization](/source/Trade_organization) 'Epsom Salt Council' recommends bathing 2 or 3 times/week, using 500–600 g (18–21 oz) Epsom salts each time.[12]

## Gallery

The crystal structure of epsomite.

Scanning electron micrograph of epsomite fibers magnified 300 times, from a sample found on a wall of a former limestone quarry cavern in Ohio.[7]

## See also

- [Magnesium sulfate](/source/Magnesium_sulfate)

## References

1. **[^](#cite_ref-1)** Warr, L.N. (2021). "IMA–CNMNC approved mineral symbols". *Mineralogical Magazine*. Vol. 85, no. 3. pp. 291–320. [Bibcode](/source/Bibcode_(identifier)):[2021MinM...85..291W](https://ui.adsabs.harvard.edu/abs/2021MinM...85..291W). [doi](/source/Doi_(identifier)):[10.1180/mgm.2021.43](https://doi.org/10.1180%2Fmgm.2021.43). [S2CID](/source/S2CID_(identifier)) [235729616](https://api.semanticscholar.org/CorpusID:235729616).

1. **[^](#cite_ref-Webmin_2-0)** ["Epsomite"](https://webmineral.com/data/Epsomite.shtml). *Web Mineral (webmineral.com)*.

1. ^ [***a***](#cite_ref-Mindat_3-0) [***b***](#cite_ref-Mindat_3-1) ["Epsomite"](http://www.mindat.org/min-1393.html). *Mindat.org*.

1. ^ [***a***](#cite_ref-HBM_4-0) [***b***](#cite_ref-HBM_4-1) [Epsomite](https://rruff.geo.arizona.edu/doclib/hom/epsomite.pdf) (PDF) (Report). Handbook of Mineralogy – via Dept. Geology, [University of Arizona](/source/University_of_Arizona).

1. ^ [***a***](#cite_ref-:0_5-0) [***b***](#cite_ref-:0_5-1) [***c***](#cite_ref-:0_5-2) [***d***](#cite_ref-:0_5-3) ["Epsomite"](https://web.archive.org/web/20060317160728/http://mineral.galleries.com/minerals/sulfates/epsomite/epsomite.htm). Sulfates. *Mineral galleries (mineral.galleries.com)*. Archived from [the original](http://mineral.galleries.com/minerals/sulfates/epsomite/epsomite.htm) on 17 March 2006.

1. **[^](#cite_ref-6)** ["The Waters of Epsom Spa"](https://pmc.ncbi.nlm.nih.gov/articles/PMC5377747/). *National Library of Medicine - PubMed Central*. [Archived](https://web.archive.org/web/20250308110132/https://pmc.ncbi.nlm.nih.gov/articles/PMC5377747/) from the original on 8 March 2025.

1. ^ [***a***](#cite_ref-:1_7-0) [***b***](#cite_ref-:1_7-1) [***c***](#cite_ref-:1_7-2) Brueck, Scott E.; Hammond, Duane R.; Zwack, Leonard M.; Hatcher, Sarah (August 2023). ["Evaluation of Occupational Exposures and Indoor Environmental Quality in an Underground Cavern Workplace"](https://www.cdc.gov/niosh/hhe/reports/pdfs/2018-0181-3389.pdf) (PDF). *U.S. National Institute for Occupational Safety and Health* ([Health Hazard Evaluation Report](/source/Health_Hazard_Evaluation_Program)). Retrieved 31 May 2024.

1. **[^](#cite_ref-8)** *McGraw-Hill Encyclopedia of Science & Technology* (10th ed.). New York, NY: McGraw-Hill. 2007. [ISBN](/source/ISBN_(identifier)) [9780071441438](https://en.wikipedia.org/wiki/Special:BookSources/9780071441438). [OCLC](/source/OCLC_(identifier)) [84152915](https://search.worldcat.org/oclc/84152915).

1. **[^](#cite_ref-9)** Giordani, Matteo; Meli, Maria Assunta; Roselli, Carla; Betti, Michele; Peruzzi, Fabio; Taussi, Marco; Valentini, Laura; Fagiolino, Ivan; Mattioli, Michele (April 2022). ["Could soluble minerals be hazardous to human health? Evidence from fibrous epsomite"](https://linkinghub.elsevier.com/retrieve/pii/S0013935121018806). *Environmental Research*. **206** 112579. [Bibcode](/source/Bibcode_(identifier)):[2022ER....20612579G](https://ui.adsabs.harvard.edu/abs/2022ER....20612579G). [doi](/source/Doi_(identifier)):[10.1016/j.envres.2021.112579](https://doi.org/10.1016%2Fj.envres.2021.112579). [hdl](/source/Hdl_(identifier)):[11576/2693349](https://hdl.handle.net/11576%2F2693349). [PMID](/source/PMID_(identifier)) [34968437](https://pubmed.ncbi.nlm.nih.gov/34968437).

1. **[^](#cite_ref-10)** Browning, Marie (1999). *Natural Soapmaking* (1st [ppb](/source/Paperback) ed.). New York, NY: Sterling. [ISBN](/source/ISBN_(identifier)) [0-8069-6289-5](https://en.wikipedia.org/wiki/Special:BookSources/0-8069-6289-5). [OCLC](/source/OCLC_(identifier)) [42598586](https://search.worldcat.org/oclc/42598586).

1. **[^](#cite_ref-11)** Rath, Linda. ["Why take an epsom salts bath?"](https://www.webmd.com/a-to-z-guides/epsom-salt-bath). *WebMD (webmd.com)*. A-to-Z guides.

1. **[^](#cite_ref-12)** [Report on absorption of magnesium sulfate](https://www.epsomsaltcouncil.org/wp-content/uploads/2015/10/report_on_absorption_of_magnesium_sulfate.pdf) (PDF) (commercial / promotional). Epsom Salt Council. October 2015 – via epsomsaltcouncil.org.

Authority control databases Encyclopedia of Modern Ukraine

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Adapted from the Wikipedia article [Epsomite](https://en.wikipedia.org/wiki/Epsomite) by Wikipedia contributors ([contributor history](https://en.wikipedia.org/wiki/Epsomite?action=history)). Available under [Creative Commons Attribution-ShareAlike 4.0 International](https://creativecommons.org/licenses/by-sa/4.0/). Changes may have been made.