Editing Magnesium (section)

=== Isotopes ===
{{Main|Isotopes of magnesium}}

Magnesium has three stable [[isotope]]s: {{chem|24|Mg}}, {{chem|25|Mg}} and {{chem|26|Mg}}. All are present in significant amounts in nature (see table of isotopes above). About 79% of Mg is {{chem|24|Mg}}. The isotope {{chem|28|Mg}} is radioactive and in the 1950s to 1970s was produced by several nuclear power plants for use in scientific experiments. This isotope has a relatively short half-life (21 hours) and its use was limited by shipping times.

The nuclide {{chem|26|Mg}} has found application in [[isotope|isotopic]] [[geology]], similar to that of aluminium. {{chem|26|Mg}} is a [[radiogenic]] daughter product of [[aluminium-26|{{chem|26|Al}}]], which has a [[half-life]] of 717,000 years. Excessive quantities of stable {{chem|26|Mg}} have been observed in the [[Ca-Al-rich inclusions]] of some [[carbonaceous chondrite]] [[meteorite]]s. This anomalous abundance is attributed to the decay of its parent {{chem|26|Al}} in the inclusions, and researchers conclude that such meteorites were formed in the [[solar nebula]] before the {{chem|26|Al}} had decayed. These are among the oldest objects in the [[Solar System]] and contain preserved information about its early history.

It is conventional to plot {{chem|26|Mg}}/{{chem|24|Mg}} against an Al/Mg ratio. In an [[isochron dating]] plot, the Al/Mg ratio plotted is {{chem|27|Al}}/{{chem|24|Mg}}. The slope of the isochron has no age significance, but indicates the initial {{chem|26|Al}}/{{chem|27|Al}} ratio in the sample at the time when the systems were separated from a common reservoir.