Magnesium oxide: Wikis


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Magnesium oxide
CAS number 1309-48-4 Yes check.svgY
PubChem 14792
RTECS number OM3850000
ATC code A02AA02
Molecular formula MgO
Molar mass 40.3044 g/mol
Appearance White powder
Odor Odorless
Density 3.58 g/cm3
Melting point

2852 °C, 3125 K, 5166 °F

Boiling point

3600 °C, 3873 K, 6512 °F

Solubility in water 0.086 g/L[2]
Solubility Soluble in acid, ammonia
insoluble in alcohol
Band gap 7.8 eV [1]
Refractive index (nD) 1.736
Crystal structure Halite (cubic), cF8
Space group Fm3m, No. 225
Octahedral (Mg2+); octahedral (O2–)
EU Index Not listed
Main hazards Metal fume fever, irritant
NFPA 704
NFPA 704.svg
Flash point Non-flammable
Related compounds
Other anions Magnesium sulfide
Other cations Beryllium oxide
Calcium oxide
Strontium oxide
Barium oxide
Related compounds Magnesium hydroxide
Magnesium nitride
 Yes check.svgY (what is this?)  (verify)
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Magnesium oxide, or magnesia, is a white solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO. It is formed by an ionic bond between one magnesium and one oxygen atom. Magnesium oxide is hygroscopic in nature and care must be taken to protect it from moisture. Magnesium hydroxide forms in the presence of water (MgO + H2O → Mg(OH)2), but it can be reversed by heating it to separate moisture.




MgO is an efficient moisture absorbent used by many libraries for preserving books. It is also one of the raw materials for making cement in dry process plants; specifically Portland cement. If too much of MgO is added, the cement may become expansive.


In medicine, magnesium oxide is used for relief of heartburn and sore stomach, as an antacid, magnesium supplement, and as a short-term laxative. It is also used to improve symptoms of indigestion. Side effects of magnesium oxide may include nausea and cramping.[3] In quantities sufficient to obtain a laxative effect, side effects of long-term use include enteroliths resulting in bowel obstruction.[4]


  • MgO is used as an insulator in industrial cables, as a basic refractory material for crucibles and as a principal fireproofing ingredient in construction materials. As a construction material, magnesium oxide wallboards have several attractive characteristics: fire resistance, moisture resistance, mold and mildew resistance, and strength.
  • It is used extensively in electrical heating as a component of "CalRod"-styled heating elements. There are several mesh sizes available and most commonly used ones are 40 and 80 mesh per the American Foundry Society. The extensive use is due to its high dielectric strength and average thermal conductivity. MgO is usually crushed and compacted with minimal airgaps or voids. The electrical heating industry also experimented with aluminium oxide, but it is not used anymore.
  • Pressed MgO is used as an optical material. It is transparent from 0.3 to 7 µm. The refractive index is 1.72 at 1 µm and the Abbe number is 53.58. It is sometimes known by the Eastman Kodak trademarked name Irtran-5, although this designation is long since obsolete. Crystalline pure MgO is available commercially and has small use in infrared optics.[6]


Magnesium oxide is easily made by burning magnesium ribbon which oxidizes in a bright white light, resulting in a powder. However, the bright flame is very hard to extinguish and it emits a harmful intensity of UV light. Inhalation of magnesium oxide fumes can cause metal fume fever.[8]


See also


  1. ^ O. E. Taurian et al. (1985). "Self-consistent electronic structures of MgO and SrO". Solid State Communications 55: 351. doi:10.1016/0038-1098(85)90622-2. 
  2. ^ Material Safety Data Sheet. Magnesium oxide
  3. ^ MedlinePlus medicinal use
  4. ^ Tatekawa Y, Nakatani K, Ishii H, et al. (1996). "Small bowel obstruction caused by a medication bezoar: report of a case". Surgery today 26 (1): 68–70. doi:10.1007/BF00311997. PMID 8680127. 
  5. ^ Tellex, Peter A.; Waldron, Jack R. (1955). "Reflectance of Magnesium Oxide". JOSA 45 (1): 19. doi:10.1364/JOSA.45.000019. 
  6. ^ Index of Refraction of Magnesium Oxide Robert E. Stephens and Irving H. Malitson
  7. ^ Waste-handling guide for WIPP
  8. ^ National Pollutant Inventory - Magnesium Oxide Fume Fact Sheet

External links

Simple English

Magnesium oxide, or magnesia, is a white solid mineral, made of one part magnesium and one part oxygen. Its chemical formula is MgO. Magnesium oxide is used by libraries to make books last longer. It is also used as an insulator for some electrical wires, and to help crucibles resist high temperatures. Magnesium oxide is also used to treat heartburn and upset stomachs.

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