High‐Precision Iron Isotope Analysis of Geological Reference Materials by High‐Resolution MC‐ICP‐MS

We report high-precision iron isotopic data for twenty-two commercially available geological reference materials, including silicates, carbonatite, shale, carbonate and clay. Accuracy was checked by analyses of synthetic solutions with known Fe isotopic compositions but different matrices ranging from felsic to ultramafic igneous rocks, high Ca and low Fe limestone, to samples enriched in transition group elements (e.g., Cu, Co and Ni). Analyses over a 2-year period of these synthetic samples and pure Fe solutions that were processed through the whole chemistry procedure yielded an average δ56Fe value of −0.001 ± 0.025‰ (2s, n = 74), identical to the expected true value of 0. This demonstrates a long-term reproducibility and accuracy of < 0.03‰ for determination of 56Fe/54Fe ratios. Reproducibility and accuracy were further confirmed by replicate measurements of the twenty-two RMs, which yielded results that perfectly match the mean values of published data within quoted uncertainties. New recommended values and associated uncertainties are presented for interlaboratory calibration in the future.