First Determination of δ53CrSRM 979 in Sixteen Geological Reference Materials Using Double Spike Thermal Ionisation Mass Spectrometry after a Two-Column Matrix Separation

We report for the first time δ⁵³Cr_{SRM 979} values in sixteen geological reference materials (RMs) with varied lithological characteristics. The measured values range from -0.24‰ ± 0.05‰ (2s) to -0.08‰ ± 0.02‰ (2s) for igneous rocks, from -0.18 ± 0.04‰ (2s) to 0.08 ± 0.03‰ (2s) for sedimentary rocks and between -0.21‰ ± 0.04‰ (2s) and -0.10‰ ± 0.04‰ (2s) for metamorphic rocks, indicating significant isotopic fractionation across these RMs. Measurements were performed using thermal ionisation mass spectrometry with a ⁵⁰Cr-⁵⁴Cr double-spike technique following a two-column matrix separation. To validate our measurement procedure, we applied it to eighteen additional well-characterised RMs. Our results are in agreement with previously reported values, with precision typically below 0.05‰ (2s). This comprehensive data set provides a valuable reference for quality assurance schemes and inter-laboratory comparisons in Cr isotopic studies.