{{Short description|Sulfate mineral}} {{use dmy dates |date = May 2024 }} {{Infobox mineral | name = Epsomite | category = [[Sulfate mineral]] | boxwidth = | boxbgcolor = | image = Epsomita 01.jpg | imagesize = | caption = Epsomite [[Speleothem|formation]] from a [[Calatayud]], [[Spain]] [[cave]] | formula = {{chem2|MgSO4*7H2O}} | IMAsymbol = Esm<ref>{{cite magazine |last=Warr |first=L.N. |year=2021 |title=IMA–CNMNC approved mineral symbols |magazine=Mineralogical Magazine |volume=85 |issue=3 |pages=291–320 |doi=10.1180/mgm.2021.43 |doi-access=free |bibcode=2021MinM...85..291W |s2cid=235729616 }}</ref> | strunz = 7.CB.40 | dana = 29.6.11.1 | system = [[Orthorhombic]] | class = Disphenoidal (222) <br/>[[H-M symbol]]: (2 2 2) | symmetry = ''P''2₁2₁2₁ | unit cell = {{mvar|a}} = 11.86, {{mvar|b}} = 11.99 <br/>{{mvar|c}} = 6.858 [Å]; {{nobr|{{mvar|Z}} {{=}} 4}} | 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 = {{mvar|n}}{{sub|{{mvar|α}}}} = 1.433 {{mvar|n}}{{sub|{{mvar|β}}}} = 1.455 {{mvar|n}}{{sub|{{mvar|γ}}}} = 1.461 | birefringence = {{mvar|δ}} = 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 = <ref name=Webmin>{{cite web |title=Epsomite |website = Web Mineral (webmineral.com) |url=https://webmineral.com/data/Epsomite.shtml }}</ref><ref name=Mindat>{{cite web |title = Epsomite |website = Mindat.org |url = http://www.mindat.org/min-1393.html }}</ref><ref name=HBM>{{cite report |title = Epsomite |series = Handbook of Mineralogy |via = Dept. Geology, [[University of Arizona]] |url = https://rruff.geo.arizona.edu/doclib/hom/epsomite.pdf }}</ref> }}
'''Epsomite''', '''Epsom salt''', or '''magnesium sulfate heptahydrate''', is a [[hydrous]] [[magnesium sulfate]] mineral with formula {{chem2|MgSO4*7H2O}}.
== Physical properties == Epsomite crystallizes in the [[orthorhombic]] system. The normal form is as massive encrustations, while [[Acicular (crystal habit)|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]] {{nobr| of 1.67.}}<ref name=":0">{{cite web |title=Epsomite |url=http://mineral.galleries.com/minerals/sulfates/epsomite/epsomite.htm |url-status=dead <!-- presumed --> |archive-url=https://web.archive.org/web/20060317160728/http://mineral.galleries.com/minerals/sulfates/epsomite/epsomite.htm |archive-date=2006-03-17 |website=Mineral galleries (mineral.galleries.com) |department=Sulfates |df=dmy-all}}</ref>
It is readily [[Solubility|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.<ref name=":0" />
The epsomite group forms a [[solid solution]] series with [[morenosite]] ({{chem|Ni|S|O|4}}·{{chem|7 H|2|O}}) and [[goslarite]] ({{chem|Zn|S|O|4}}·{{chem|7 H|2|O}}). This series' members bear the same structure as either the [[nickel]], [[zinc]], or [[magnesium]] cations occupying similar positions in the lattice. Intermediate compositions containing more than one of these elements are also known.<ref name="Mindat" />
== Etymology == In 1618, a well was dug by a local farmer on [[Epsom]] common, half a mile west of Epsom, [[Surrey]], [[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]]. In 1695 Dr. Nehemiah Grew published his study on the water's composition, establishing Epsom salts as a medical remedy.<ref>{{cite web |title=The Waters of Epsom Spa |url=https://pmc.ncbi.nlm.nih.gov/articles/PMC5377747/ |url-status=live |archive-url=https://web.archive.org/web/20250308110132/https://pmc.ncbi.nlm.nih.gov/articles/PMC5377747/ |archive-date=2025-03-08 |website=National Library of Medicine - PubMed Central}}</ref> It was later systematically described in 1806.<ref name=":0" /> It has been also referred to as "cave cotton" when in its fibrous form.<ref name=":1" />
==Occurrence== Epsomite forms as [[encrustation]]s or [[efflorescence]]s 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.<ref name=":0" /><ref>{{cite book |title=McGraw-Hill Encyclopedia of Science & Technology |edition=10th |year=2007 |place=New York, NY |publisher=McGraw-Hill |isbn=9780071441438 |oclc=84152915}}</ref> It occurs in association with [[melanterite]], [[gypsum]], [[halotrichite]], [[pickeringite]], [[alunogen]], [[rozenite]], and [[mirabilite]].<ref name=HBM/>
Naturally occurring epsomite in caverns can potentially produce [[particulates]] of inhalable size, and may contain significant amounts of toxic impurities.<ref name=":1" /><ref>{{Cite journal |last1=Giordani |first1=Matteo |last2=Meli |first2=Maria Assunta |last3=Roselli |first3=Carla |last4=Betti |first4=Michele |last5=Peruzzi |first5=Fabio |last6=Taussi |first6=Marco |last7=Valentini |first7=Laura |last8=Fagiolino |first8=Ivan |last9=Mattioli |first9=Michele |date=April 2022 |title=Could soluble minerals be hazardous to human health? Evidence from fibrous epsomite |url=https://linkinghub.elsevier.com/retrieve/pii/S0013935121018806 |journal=Environmental Research |language=en |volume=206 |article-number=112579 |doi=10.1016/j.envres.2021.112579|pmid=34968437 |bibcode=2022ER....20612579G |hdl=11576/2693349 |hdl-access=free }}</ref>
==Uses== Epsom salt is commonly sold as the main ingredient in [[Bath salts|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.<ref>{{cite book |last=Browning |first=Marie |year=1999 |title=Natural Soapmaking |edition=1st [[paperback|ppb]] |place=New York, NY |publisher=Sterling |isbn=0-8069-6289-5 |oclc=42598586 }}</ref>
Research on [[Topical medication|topical]] magnesium (for example Epsom salt baths) is very limited.<ref>{{cite web |last1=Rath |first1=Linda |title=Why take an epsom salts bath? |series = A-to-Z guides |website=WebMD (webmd.com) |lang=en-US |url=https://www.webmd.com/a-to-z-guides/epsom-salt-bath }}</ref> The [[trade organization]] 'Epsom Salt Council' recommends bathing 2 or 3 times/week, using {{cvt|500-600|g|oz}} Epsom salts each time.<ref>{{cite report |title = Report on absorption of magnesium sulfate |publisher = Epsom Salt Council |date = October 2015 |type = commercial / promotional |url = https://www.epsomsaltcouncil.org/wp-content/uploads/2015/10/report_on_absorption_of_magnesium_sulfate.pdf |via = epsomsaltcouncil.org }}</ref>
==Gallery== [[File:Epsomite crystal structure.png|thumb|left|350px|The crystal structure of epsomite.]]
[[File:Epsomite cave cotton 2.png|thumb|left|Scanning electron micrograph of epsomite fibers magnified 300 times, from a sample found on a wall of a former limestone quarry cavern in Ohio.<ref name=":1">{{Cite web |first1=Scott E. |last1=Brueck |first2=Duane R. |last2=Hammond |first3=Leonard M. |last3=Zwack |first4=Sarah |last4=Hatcher|date=August 2023 |title=Evaluation of Occupational Exposures and Indoor Environmental Quality in an Underground Cavern Workplace |url=https://www.cdc.gov/niosh/hhe/reports/pdfs/2018-0181-3389.pdf |access-date=2024-05-31 |website=U.S. National Institute for Occupational Safety and Health |type=[[Health Hazard Evaluation Program|Health Hazard Evaluation Report]]}}</ref>]]
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==See also== * [[Magnesium sulfate]]
==References== {{reflist|25em}}{{Authority control}}
[[Category:Magnesium minerals]] [[Category:Sulfate minerals]] [[Category:Heptahydrate minerals]] [[Category:Cave minerals]] [[Category:Orthorhombic minerals]] [[Category:Minerals in space group 19]] [[Category:Evaporite]]