((Infobox element
|name   =magnesium
|symbol =Mg
|Z      =12
|number =12
|abundance=
|abundance in earth's crust=
|abundance in oceans=
|abundance in solar system=
|left=[[sodium]]
|right=[[aluminium]]
|above=[[beryllium|Be]]
|below=[[calcium|Ca]]
|appearance=shiny grey solid
|image name=CSIRO ScienceImage 2893 Crystalised magnesium.jpg
|electrons per shell=2, 8, 2
|phase=
|phase comment=
|density gplstp=
|density gpcm3nrt=1.738
|density gpcm3nrt 2=
|density gpcm3mp=1.584
|melting point K=923
|melting point C=650
|melting point F=1202
|boiling point K=1363
|boiling point C=1091
|boiling point F=1994
|triple point K=
|triple point kPa=
|critical point K=
|critical point MPa=
|heat fusion=8.48
|heat fusion 2=
|heat vaporization=128
|heat capacity=24.869<ref>Rumble, p. 4.61</ref>
|vapor pressure 1=701
|vapor pressure 10=773
|vapor pressure 100=861
|vapor pressure 1 k=971
|vapor pressure 10 k=1132
|vapor pressure 100 k=1361
|vapor pressure comment=
|crystal structure=hexagonal close packed
|electronegativity=1.31
|number of ionization energies=4
|ionization energy 1=737.7
|ionization energy 2=1450.7
|ionization energy 3=7732.7
|atomic radius=160
|covalent radius=141±7
|Van der Waals radius=173
|magnetic ordering=[[paramagnetism|paramagnetic]]
|electrical resistivity=
|electrical resistivity unit prefix=n
|electrical resistivity at 0=
|electrical resistivity at 20=43.9<ref>Rumble, p. 12.28</ref>
|thermal conductivity=156<ref>Rumble, p. 12.137</ref>
|thermal conductivity 2=
|thermal diffusivity=
|thermal expansion=
|thermal expansion at 25=24.8<ref>Rumble, p. 12.135</ref>
|speed of sound=
|speed of sound rod at 20=
|speed of sound rod at r.t.=4940
|speed of sound rod at r.t. comment=(annealed)
|magnetic susceptibility= ((val|+13.1|e=−6))
|magnetic susceptibility ref=&#x20;(298&nbsp;K)<ref>Rumble, p. 4.70</ref>
|Young's modulus=45
|Shear modulus=17
|Bulk modulus=35.4<ref>((cite book|author=Gschneider, K. A. |title=Physical Properties and Interrelationships of Metallic and Semimetallic Elements|volume=16|doi=10.1016/S0081-1947(08)60518-4|page=308|series=Solid State Physics|year=1964|isbn=9780126077162))</ref>
|Poisson ratio=0.290
|Mohs hardness=1–2.5
|Vickers hardness=
|Brinell hardness=44–260
|CAS number=7439-95-4
|naming=after [[Magnesia (regional unit)|Magnesia]], Greece<ref name=r1/>
|predicted by=
|prediction date=
|discovered by=[[Joseph Black]]
|discovery date=1755<ref name=r1>Rumble, p. 4.19</ref>
|first isolation by=[[Humphry Davy]]
|first isolation date=1808<ref name=r1/>
|named by=
|named date=
|history comment label=
|history comment=
|QID=Q660
))<!--

--><noinclude>
((Infobox element/element navigation|symbol=Mg))
((Template reference list))
((documentation|1=Template:Infobox element/doc))
</noinclude>