22 isotopic determinations of magnesium have been done on minerals, rocks and lavas of very different origins. These measurements do not show any isotopic fractionation for rocks of the major cycle, except may be for minerals formed by hydrothermal processes and for carnallite which shows a definite enrichment in ²⁴Mg.

For the rocks without isotopic fractionation the authors found the mean values of 0,140 ± 0,007 for the ratio 26/24 and 0,127 ± 0,007 for the ratio 25/24.