Calculation and Illustration of Uncertainty in Geochemical Analyses

The uncertainty in chemical analyses resulting from precision error should be evaluated and indicated, and error bars should be placed on analytical data when they are plotted in the various diagrams used in geochemistry. The corresponding uncertainty in the sums and quotients that are commonly used (e.g., Na2O + K2O, K/Rb, Fe/(Fe + Mg)) can be readily calculated by use of the superposition-of-errors theorem, allowing error bars to be placed on these concentration variables as well. Knowledge of precision error is particularly important when comparing samples that differ only slightly in chemical composition.