Magnesium oxide (MgO), or magnesia, is a white hygroscopic solid mineral that occurs naturally as periclase and is a source of magnesium (see also oxide). It has an empirical formula of MgO and consists of a lattice of Mg2+ ions and O2− ions held together by ionic bonding. Magnesium hydroxide forms in the presence of water (MgO + H2O → Mg(OH)2), but it can be reversed by heating it to remove moisture. Magnesium oxide was historically known as magnesia alba (literally, the white mineral from Magnesia), to differentiate it from magnesia negra, a black mineral containing what is now known as manganese. Related oxides
While "magnesium oxide" normally refers to MgO, magnesium peroxide MgO2 is also known as a compound. According to evolutionary crystal structure prediction, MgO2 is thermodynamically stable at pressures above 116 GPa (gigapascals), and a semiconducting suboxide Mg3O2 is thermodynamically stable above 500 GPa. Because of its stability, MgO is used as a model system for investigating vibrational properties of crystals. Electric properties
Pure MgO is not conductive and has a high resistance to electric current at room temperature. The pure powder of MgO has a relative permettivity inbetween 3.2 to 9.9 
  
    
      
        k
      
    
    {\displaystyle k}
   with an approximate dielectric loss of tan(δ) > 2.16x103 at 1kHz. Production
Magnesium oxide is produced by the calcination of magnesium carbonate or magnesium hydroxide.
Periorbital hyperpigmentation, also known as hereditary dark circles, is characterized by darker skin around the eyes caused by the presence of additional melanin. It is an extremely common hereditary human characteristic and is frequently found on individuals with dark skin. Periorbital hyperpigmentation is most prevalent within the 16–25 age group. See also
Eye shadow
Kohl (cosmetics)
Freckles

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