Magnesium is almost always found in compound form in nature, with the most abundant source being ocean water. Normally, magnesium is found as magnesite, which is magnesium carbonate, or dolomite. In seawater, magnesium is the third most abundant mineral behind both sodium and chloride.
Magnesium can also be found in some foods and is an important part of a healthy diet. Most humans do not get the amount of magnesium they need from food. The best natural source of magnesium in the diet is green leafy vegetables.
Outside of diet, magnesium is used in a number of applications. It is often combined with aluminum to make a strong metal alloy. Magnesium is a very light metal, the second lightest alkaline earth metal. The element normally forms ionic compounds, like magnesium hydroxide, which is more commonly known by the name milk of magnesia.
Another common household item that contains magnesium is Epsom salts. These are normally used as bath salts. The compound in the salts is officially called magnesium sulfate hepahydrate. This form of the element was discovered by a farmer in 1618 in Epsom, England. His cows refused to drink the water from a specific mineral well on his property, indicating that there was something abnormal in the water. Epsom salts are still used today to help with minor skin abrasions and irritations.