According to Chemical Dictionary, the chemical formula for Milk of Magnesia is Mg(OH)2. It is also referred to as magnesium hydroxide, magnesium hydrate or magnesia magma.
Milk of Magnesia is most commonly used as a laxative and as an antacid to neutralize stomach acid. This releases much of the body's potassium stores. Failure to replenish the lost potassium often leads to muscle cramping.
Milk of Magnesia can also be used as a bleaching solution to whiten clothes and as a non-antiperspirant deodorant.
Industrially, magnesium hydroxide is used as a non-hazardous alkali to neutralize acidic waste-water. It is also instrumental in growing new reefs called Seacrete or Biorock.