|Isotope||Atomic mass (Da)||Isotopic abundance (amount fraction)|
|24Mg||23.985 041 70(9)||[0.7888, 0.7905]|
|25Mg||24.985 8370(3)||[0.099 88, 0.100 34]|
|26Mg||25.982 5930(2)||[0.1096, 0.1109]|
In 2011, the Commission has changed the standard atomic weight of magnesium to Ar(Mg) = [24.304, 24.307] based on an evaluation of the effect of variation in isotopic abundances in normal materials upon the atomic weight of magnesium. This change is intended to emphasize the fact that the atomic weight of magnesium is not a constant of nature, but depends upon the source of the material. The standard atomic weight was determined by combining (1) the best calibrated isotope-ratio measurement of magnesium in DSM3 isotopic reference material (a mono-elemental nitric solution of magnesium), and (2) the relative isotope-ratio differences between other magnesium-bearing materials and DSM3. Many of the δ26/24Mg measurements reported herein were made using DSM3 as the standard. However, the Commission does not recommend DSM3 as an international measurement standard for δ26/24Mg measurements because it is not readily available to laboratories worldwide.
Graphical plot (SNIF diagram) of isotopic-abundance variation and atomic-weight variation for magnesium is shown below.
Atomic weights of the elements 2011 by M.E. Wieser et al. Pure Appl. Chem. 2013 (85) 1047-1078
© IUPAC 2003, 2013