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Periodic Table--Magnesium

Magnesium-26 is a stable isotope that has found application in isotopic geology, similar to that of aluminum. 26Mg is a radiogenic daughter product of 26Al (t1/2 = 0.72x106 yr). Large enrichments of stable 26Mg have been observed in the Ca-Al-rich inclusions of the carbonaceous chondrite meteorite Allende (Hutcheon, 1982; Huneke et al., 1983). The anomalous abundance of 26Mg is attributed to the decay of its parent 26Al in the inclusions. Therefore, the meteorite must have formed in the solar nebula before the 26Al had decayed. Hence, these fragments are among the oldest objects in the solar system and have preserved information about its earliest history.

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

Source of text: This review was assembled by Eric Caldwell, primarily from Faure (1986) and Dicken (1995).

Dicken, A.P. (1995). Radiogenic Isotope Geology. Cambridge University Press, New York, 452 p.
Faure, G. (1986). Principles of Isotope Geology, Second Edition. John Wiley and Sons, New York. 589 p.
Huneke, J.C., Armstrong, J.T. and Wasserburg, G.J. (1983). "FUN with PANURGE: High mass resolution ion microprobe measurements of Mg in Allende inclusions." Geochim. et Cosmochim. Acta, 47: 1635-1650.
Hutcheon, I.D. (1982). "Ion probe magnesium isotopic measurements of Allende inclusions." In: L.A. Currie (Ed.), Nuclear and chemical dating techniques: Interpreting the environmental record, 96-128. Amer. Chem. Soc. Symposium Series, No. 176, 516 p.
Lee, T., Papanastassiou, D.A. and Wasserburg, G.J. (1976). "Demonstration of 26Mg excess in Allende and evidence for 26Al." Geophys. Res. Lett., 3: 109-113.
Steele, I.M. and Hutcheon, I.D. (1979). "Anatomy of Allende inclusions: mineralogy and Mg isotopes in two Ca-Al-rich inclusions." In: Lunar Planet. Sci., X: Lunar Planet. Inst., 1166-1168 (abstract).
Wasserburg, G.J., Lee, T. and Papanastassiou, D.A. (1977). "Correlated O and Mg isotopic anomalies in Allende inclusions: II magnesium." Geophys. Res. Lett., 4: 299-302.
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Fundamentals of Stable Isotope Geochemistry
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