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Roger Weller, geology instructor

epsom salts
by Barry  Eastman
Physical Geology
Spring 2011


Epsom Salt


     Before Epsom Salt was officially documented as a discovery, people for centuries ventured to these mineral springs with miraculous healing properties.  By the 1600’s the Epsom mineral springs became even more popular with the establishment of spas, although today there is little to be seen apart from from a water pump.  One such individual that profited on the Epsom springs was the naturalist, Nehemiah Grew (1628-1711).



                   Nehemiah Grew, younger days. 



             The term Epsom salt was coined by Grew who in 1695 named the mineral found in the bitter saline spring waters after the nearest town to its vicinity, Epsom, in Surrey, England.  He also had acquired a royal patented for the collection and sale of the mineral compound.  In addition, the name of the town was also derived from Ebba’s ham, Ebba was a Saxon landowner.

So, what is Epsom salt?

Epsom’s salt, or its mineral name, Epsomite, which occurs naturally as heptahydrous magnesium sulfate mineral, a hydrated form of Magnesium Sulfate (MgSO4).  Its chemical compound is magnesium, sulfur, oxygen, with seven water molecules, and the chemical formula is (MgSO4 7H2O).


                   Epsom Salt


     Magnesium sulfate in its unaltered state is called anhydrous magnesium sulfate, which means having no water. 

Its physical appearance is that of a white powdery material.





                                                Magnesium sulfate                         anhydrous magnesium sulfate   

     One of its properties is it readily absorbs water, and so will Epsom salt.  Furthermore, if an anhydrous magnesium sulfate compound accepts water molecules it becomes hydrated, and thus it becomes a hydrated magnesium sulfate compound, which is the basis for other hydrated mineral forms like Epsomite.

The following is a list of other hydrated magnesium sulfates.

Notice the number of water molecules (H2O) in their chemical formula.  

Related minerals:

 among evaporate deposits.


 contains copper.

§  Meridianiite, (MgSO4 * 11H2O), It is the most recent terrestrial find and believed to also occur on the planet Mars.




Starkeyite                                Kiesert   

What environment does it form?

     Epsom Salt, or Bitter salts, forms as a powdery, fibrous or globular crust growing as efflorescence, (flowering out), on cave walls, sulfide, coal, and metal mines from saline springs, or depositions of sulfur and magnesium-rich water due to mining operations.  Salt deposits also occur among hot springs. Epsomite formations are mostly found in arid regions located in dry caves and alike which inhibits the dissolution of the mineral due to its hydrophilic personality, i.e., water soluble.


     It also been noticed among volcanoes’ fumaroles such as Mt. Vesuvius in Italy.  Epsomite also occurs in South Africa as unusual marine salt deposits that form in sedimentary beds.





     The forming of Epsom salt crystals is a straightforward process.  A source of water is needed like a hot springs.

The springs needs to be hot enough to fully dissolve the magnesium sulfate, that is, an increase of temperature also increases the amount of space between each molecule.  This will create a condition of saturation is when all available space between molecules has been filled.  Later as the water cools the space decreases forcing the molecules together at which time it causes the crystals to form and separate from the water.

     To reference this topic along with an experiment in the process of how crystals grow view the following:                                            

H:\GEOLOGY\How Do Epsom Salt Crystals Form  eHow_com.mht

How is Epsom Salt obtained?

     Originally, Epsom salt was obtained by boiling down the mineral waters at Epsom, England; afterwards the mineral was acquired from sea water using the same methods.  Ironically this method has not changed except for the material from which Epsom salt is prepared.  Besides the usual sources that Epsom salt is obtained it is also prepared from other sources such as Kieserite mineral and Dolomite.  Magnesium Sulfate, Epsom salt, is obtained by dissolving the mineral in water at 200oF (90oC) then allow the solution to cool thereby the process of filtration the crystals are removed.  Another source is dolomite.  Since Dolomite belongs to a group known as Salts, and consists of the elements calcium, magnesium, carbon, and oxygen in which it takes the form of carbonate of calcium and magnesium.  Dolomite is a suitable source to obtain Epsom salt because it consists of magnesium, sulfur, and oxygen. The process of extraction is similar. 



     Epsomite was found as crusts produced by thermal springs in Epsom, Surrey, England, which is the locality it is named after. It occurs in certain areas in the Sahara Desert of Africa, the desert of Central Australia, and the Atacama Desert of Chile, where it sometimes forms thick beds.
     In the U.S., it occurs in the saline lake beds on Kruger Mountain, near Oroville, Okanogan Co, Washington, and in the Carlsbad Caverns of New Mexico. Other occurrences are the Kalkar quarry, Santa Cruz Co., California; the White Caps mine in Manhattan, Nye Co., Nevada; Majuba Hill mine, Pershing Co., Nevada; and Bisbee, Cochise Co., Arizona.


           Prismatic     Modified Prismatic








     The areas that Epsom salt can be used is astonishing and just too numerous to list them all, and the secret to its value?  Is that Epsom salt is artificially made salt of magnesium and is forever trying to rid itself of the sulfur and join with its original partner, carbon.  Because of this affinity for carbon it readily exchanges sulfur for carbon when possible.  Hence this is the human body’s cure-all because since the body takes in forms of carbons in the forms of food stuffs and breathable air it then becomes a crude form of carbon.  The magnesium dumps the sulfur and connects with the carbon units thus facilitating excretion of waste products from the body’s systems.

Epsom salt truly is a Miracle Mineral.




     H:\GEOLOGY\How Do Epsom Salt Crystals Form eHow_com.mht


     ...Take what you say with a crystal  of Epsom Salt!  Ep-som good Salt! Yo!