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of Magnesium Hydroxide


of Magnesium Hydroxide

Chemical formula = Mg(OH)2

Molecular weight = 58.3197 g/mol

Density = 2.345 g/cm³ 

Solubility = 5.61 x 10⁻¹²

CAS number = 1309.42.8

Magnesium hydroxide (Mg(OH)2) decomposes to magnesium oxide at 360°C

Common applications include:

  • Pharmaceutical: in antacids and laxatives

  • Antibacterial: in natural antiperspirants and deodorants

  • Industrial: in neutralizing acidic wastewater; in buffering pH, and as an alkalinity source

  • Industrial: in fire retardants and smoke suppressors

  • Chemical: in producing other Mg compounds

  • Nutritional: in human dietary supplements and animal feed


Magnesium was first discovered in the region or prefecture of Magnesia, Greece. Alchemists were familiar with magnesia alba (white magnesia) in the form of magnesium carbonate (Mg(CO)3; the mineral magnesite) since ancient times and throughout the Middle Ages and associated it with the fourth element of alchemy, Earth. Magnesium compounds had been used for medicinal and spiritual purposes for centuries. Joseph Black discovered elemental magnesium in 1755, adding it to the periodic table. In1808, Sir Humphry Davy was the first to isolate a minimal amount of the element. However, Antoine-Alexandre-Brutus Busy, a French scientist, is regarded as the first to produce a substantial amount, documenting its properties. It is the lightest structural metal and around 75% lighter than steel, 50% lighter than titanium, and 35% lighter than aluminum.


Magnesium is a silvery-gray metal, the 8th most abundant element in the universe, and it constitutes almost 2.5% of the earth's crust as magnesium oxide. Magnesium makes up approximately 0.13% of total seawater weight. Due to its relatively high reactivity, it only occurs naturally combined with other elements.

Magnesium Hydroxide is an inorganic magnesium compound, occurring naturally as brucite. Archibald Bruce, an American mineralogist, first discovered it in the early nineteenth century. Today, magnesium hydroxide or Mg(OH)2 is found in a variety of technical and manufacturing applications, in pharmaceutical goods, and environmental applications.


Most people associate magnesium hydroxide with the popular antacid, Milk of Magnesia. The development of Mg(OH)2 for medicinal remedies has a complicated history:

  • In1818, John Callen, an American inventor, was granted a patent for the chemical compound, magnesium hydroxide.

  • In 1873, another patent was issued for a condensed solution of fluid magnesium hydroxide after first being used in 1829 by Sir James Murray to treat Irish Lords for stomach pain.

  • A year earlier, in 1872, Charles Henry Phillips developed a suspension of magnesium hydroxide with a specific weight per volume and coined it, "Milk of Magnesia."

  • Since 1995, the USPTO lists Bayer as the registered owner of both the formulation and name(s) Milk of Magnesia™ and Phillips Milk of Magnesia™.


fascinating facts.

about Magnesium and Magnesium Hydroxide

  • It takes 770lbs of seawater to produce 1lb of elemental magnesium.

  • The Griesheim Co. first successfully alloyed magnesium in 1908—a mixture of magnesium and aluminum.

  • Magnesium has the highest strength-to-weight ratio of all structural metal alloys.

  • Elemental magnesium is virtually inflammable unless it exceeds its melting point, from then on, maintaining a constant source of heat.

  • Magnesium hydroxide is used to help supply needed nutrients and conditions in wastewater treatment that are favorable for bacterial growth.

  • Magnesium hydroxide aids in creating Biorock™, an artificial reef.

  • The ionic exchange and chemical reaction between soluble magnesium salts and alkali hydroxides create magnesium hydroxide.

  • Magnesium hydroxide is a popular antibacterial ingredient in natural deodorants.

  • Magnesium hydroxide acts as a natural fire retardant—its unique endothermic decomposition postpones ignition, releasing water that dilutes combustible gasses while suppressing oxygen at the same time.


to Magnesium and Magnesium Hydroxide


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