Magnesium sulphate (MgSO4), commonly known as Epsom salt.
 
Primarily used as a foliar and irrigated fertiliser in the agriculture sector where it improves soil fertility, creating an environment conducive to growth.
 
Another industry it is commonly used in is the animal nutrition industry, where it is used in animal feed (feed grade) to aid the metabolism of carbohydrates, lipids (fats) and proteins and for nerve activity and muscle contraction.