Magnesium sulfate (or magnesium sulphate) is an inorganic salt (chemical compound) containing magnesium, sulfur and oxygen, with the formula MgSO4. It is often encountered as the heptahydrate sulfate mineral epsomite (MgSO4·7H2O), commonly called Epsom salt, taking its name from a bitter saline spring in Epsom in Surrey, England, where the salt was produced from the springs that arise where the porous chalk of the North Downs meets non-porous London clay. The monohydrate, MgSO4·H2O is found as the mineral kieserite. The overall global annual usage in the mid 1970s of the monohydrate was 2.3 million tons, of which the majority was used in agriculture.

The dictionary meaning is not relevant to here

  • Which dictionary meaning? Without knowing which dictionary you checked, and what you found there, it's a little hard to figure out why you came to the wrong conclusion. – J.R. Nov 7 '14 at 9:08

Actually, the definition encountered in the dictionary is relevant here.

Collins English Dictionary defines encounter as:


to come upon or meet casually or unexpectedly

to come into conflict with (an enemy, army, etc) in battle or contest

(transitive) to be faced with; contend with ⇒ he encounters many obstacles in his work

It simply means that even though the chemical formula for magnesium sulphate is MgSO4; it's often found/encountered in nature as MgSO4·7H2O. And it indeed is not the only compound found in nature this way. Borax (sodium borate) is actually found in different ways depending on the amount of water it contains.

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