Magnesium sulfate

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Magnesium sulfate
Anhydrous magnesium sulfate
style="background: #F8EABA; text-align: center;" colspan="2" | Identifiers
CAS number 7487-88-9 YesY
14168-73-1 (monohydrate)
24378-31-2 (tetrahydrate)
15553-21-6 (pentahydrate)
13778-97-7 (hexahydrate)
10034-99-8 (heptahydrate)
PubChem 24083
ChemSpider 22515
RTECS number OM4500000
style="background: #F8EABA; text-align: center;" colspan="2" | Properties
Molecular formula MgSO4
Molar mass 120.366 g/mol (anhydrous)
246.47 g/mol (heptahydrate)
Appearance white crystalline solid
Density 2.66 g/cm3 (anhydrous)
2.445 g/cm3 (monohydrate)
1.68 g/cm3 (heptahydrate)
Melting point

1124 °C (anhydrous, decomp)
200 °C (monohydrate, decomp)
150 °C (heptahydrate, decomp)

Solubility in water anhydrous
269 g/L (0 °C)
255 g/L (20 °C)
710 g/L (20 °C)
Solubility 0.116 g/L (18 °C, ether)
slightly soluble in alcohol, glycerol
insoluble in acetone
Refractive index (nD) 1.523 (monohydrate)
1.433 (heptahydrate)
style="background: #F8EABA; text-align: center;" colspan="2" | Structure
Crystal structure monoclinic (hydrate)
style="background: #F8EABA; text-align: center;" colspan="2" | Hazards
MSDS External MSDS
EU Index Not listed
style="background: #F8EABA; text-align: center;" colspan="2" | Related compounds
Other cations Beryllium sulfate
Calcium sulfate
Strontium sulfate
Barium sulfate
 YesY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Magnesium sulfate (or magnesium sulphate) is a chemical compound containing magnesium, sulfur and oxygen, with the formula MgSO4. It is often encountered as the heptahydrate epsomite (MgSO4·7H2O), commonly called "Epsom salt". Another hydrate form is kieserite.

Anhydrous magnesium sulfate is used as a drying agent. Since the anhydrous form is hygroscopic (readily absorbs water from the air) and is therefore difficult to weigh accurately, the hydrate is often preferred when preparing solutions, for example in medical preparations. Epsom salt has been traditionally used as a component of bath salts.


Magnesium sulfate is the primary substance that causes the absorption of sound in seawater.[1] Absorption, in this case, means the conversion of acoustic energy to heat energy. The conversion is a strong function of frequency. Lower frequencies are less affected by the salt, so that the acoustic energy travels much farther in the ocean. Boric acid also contributes to absorption; but the most abundant salt in seawater, sodium chloride, has no known effect on sound absorption.


Almost all known mineralogical forms of MgSO4 occur as hydrates. Epsomite is the natural analogue of "Epsom salt". Another heptahydrate, the copper-containing mineral alpersite (Mg,Cu)SO4·7H2O[2], was also recently recognized. Both are however not the highest known hydrates of MgSO4, due to the recent terrestrial find of meridianiite, MgSO4·11H2O, which is thought to also occur on Mars. Hexahydrite is the next lower (6) hydrate. Three next lower hydrates - pentahydrite (5), starkeyite (4) and especially sanderite (2) are more rarely found. Kieserite is a monohydrate and is common among evaporitic deposits. Anhydrous magnesium sulfate was reported from some burning coal dumps, but never treated as a mineral.

The pH of hydrates is average 6.0 (5.5 to 6.5). Magnesium hydrates have, like Copper(II) sulfate, coordinated water. [3]


Magnesium sulfates are common minerals in geological environments. Their occurrence is mostly connected with supergene processes. Some of them are also important constituents of evaporitic potassium-magnesium (K-Mg) salts deposits.


In agriculture and gardening, magnesium sulfate is used to correct magnesium deficiency in soil, since magnesium is an essential element in the chlorophyll molecule. It is most commonly applied to potted plants, or to magnesium-hungry crops, such as potatoes, roses, tomatoes, peppers and cannabis. The advantage of magnesium sulfate over other magnesium soil amendments (such as dolomitic lime) is its high solubility.

Anhydrous magnesium sulfate is commonly used as a desiccant in organic synthesis due to its affinity for water. During work-up, an organic phase is saturated with magnesium sulfate until it no longer forms clumps. The hydrated solid is then removed with filtration or decantation. Other inorganic sulfate salts such as sodium sulfate and calcium sulfate may also be used in the same way.

Magnesium sulfate is used in bath salts, particularly in flotation therapy where high concentrations raise the bath water's specific gravity, effectively making the body more buoyant. This property is also used to restore some Lava lamps damaged by being shaken by exchanging the water and adding drops of a concentrated solution until sustainable buoyancy is reached. Traditionally, it is also used to prepare foot baths, intended to soothe sore feet. The reason for the inclusion of the salt is partially cosmetic: the increase in ionic strength prevents some of the temporary skin wrinkling ("pruning" – partial maceration) which is caused by prolonged immersion of extremities in pure water. However, magnesium sulfate can also be absorbed into the skin, reducing inflammation. It is also sometimes found in bottled mineral water, and accordingly is sometimes listed in the contents thereof. It may also be used as a coagulant for making tofu.[4]

Magnesium sulfate heptahydrate is also used to maintain the magnesium concentration in marine aquaria which contain large amounts of stony corals as it is slowly depleted in their calcification process. In a magnesium-deficient marine aquarium calcium and alkalinity concentrations are very difficult to control because not enough magnesium is present to stabilize these ions in the saltwater and prevent their spontaneous precipitation into calcium carbonate.[5]

Magnesium sulfate is used as the electrolyte to prepare copper sulfate. A magnesium sulfate solution is electrolyzed with a copper anode to form copper sulfate, magnesium hydroxide, and hydrogen:

Cu + MgSO4 + 2 H2O → H2 + CuSO4 + Mg(OH)2

Medical use

Oral magnesium sulfate is commonly used as a saline laxative. Epsom salt is also available in a gel form for topical application in treating aches and pains.

Indications for its internal use are

Indications for topical use are

  • Magnesium sulfate paste has been used as an agent for dehydrating (drawing) boils, carbuncles, and abscesses.[15]
  • Magnesium sulfate solution has also been shown to be an effective aid in the fight against blemishes and acne when applied directly to problematic areas, usually in poultice form.[16] If combined with water and made into a cream, it can be applied to the face to remove blackheads.
  • Soaking in a warm bath containing Epsom salt (magnesium sulfate) can be beneficial to soothe, relax,and relieve herpes outbreak symptoms, such as itching and lesions relating to genital herpes and shingles.[17][18]

See also


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cs:Síran hořečnatý

de:Magnesiumsulfat et:Magneesiumsulfaat es:Sulfato de magnesio fr:Sulfate de magnésium it:Solfato di magnesio he:מגנזיום גופרתי hu:Magnézium-szulfát nl:Magnesiumsulfaat ja:硫酸マグネシウム no:Magnesiumsulfat pl:Siarczan magnezu pt:Sulfato de magnésio ro:Sulfat de magneziu ru:Сульфат магния (лекарственное средство) ru:Гептагидрат сульфата магния sl:Projekt:Magnezijev sulfat sr:Магнезијум сулфат fi:Magnesiumsulfaatti sv:Magnesiumsulfat th:แมกนีเซียมซัลเฟต

  1. "Underlying physics and mechanisms for the absorption of sound in seawater". Retrieved 2009-07-06. 
  2. Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  3. Lucia Odochian Study of the nature of the crystallization water in some magnesium hydrates by thermal methods J. of Thermal Analysis and Calorimetry ; Volume 45, Number 6 / December, 1995. doi:10.1007/BF02547437
  4. "Process for producing packed tofu". 
  5. "Do-It-Yourself Magnesium Supplements for the Reef Aquarium". Reefkeeping. 2006. Retrieved 2008-03-14. 
  6. "Pharmaceutical Information - MAGNESIUM SULFATE". RxMed. Retrieved 2009-07-06. 
  7. "When clicking citation, it is listed under ''Other medicinal and home uses''". 2007-01-04. Retrieved 2009-07-06. 
  8. 8.0 8.1 Blitz M, Blitz S, Hughes R, Diner B, Beasley R, Knopp J, Rowe BH. Aerosolized magnesium sulfate for acute asthma: a systematic review. Chest 2005;128:337-44. PMID 16002955.
  9. Rosemary Waring Absorption of magnesium sulphate through the skin (republished by the Epsom Salt Council), 2004
  10. jab averts pregnancy danger', BBC News, 30 May 2002
  11. "Magnesium sulfate for preterm labor". 2007-01-19. Retrieved 2009-07-06. 
  12. Lua error in package.lua at line 80: module 'Module:Citation/CS1/Suggestions' not found.
  13. "Epsom salt can prevent cerebral palsy: U.S. study". 2008-01-31. Retrieved 2009-07-06. 
  14. "BARIUM CHLORIDE DIHYDRATE 4. First Aid Measures". Retrieved 2009-07-06. 
  15. "How to Get Rid of Boils". Retrieved 2009-07-06. 
  16. "Acne guide". Retrieved 2009-07-06. 
  17. "Herpes Home Remedies" Herpes and Cold Sores Support Network
  18. "McKinley Health Center - Genital Herpes - University of Illinois" McKinley Health Center, University of Illinois