Column Descriptions Relative Isotopic Standard Isotope Atomic Mass Composition Atomic Weight Notes _________________________________________________________________________ 12 Mg 24 23.985041697(14) 0.7899(4) [24.304,24.307] 25 24.985836976(50) 0.1000(1) 26 25.982592968(31) 0.1101(3) _________________________________________________________________________NIST | Physical Measurement Laboratory | Physical Reference Data | Atomic Weights and Isotopic Compositions Main Page