First Determination of <scp>δ⁵³Cr_SRM</scp>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 δ 53 Cr SRM 979 values in sixteen geological reference materials (RMs) with varied lithological characteristics. The measured values range from ‐0.24‰ ± 0.05‰ (2 s ) to ‐0.08‰ ± 0.02‰ (2 s ) for igneous rocks, from ‐0.18 ± 0.04‰ (2 s ) to 0.08 ± 0.03‰ (2 s ) for sedimentary rocks and between ‐0.21‰ ± 0.04‰ (2 s ) and ‐0.10‰ ± 0.04‰ (2 s ) for metamorphic rocks, indicating significant isotopic fractionation across these RMs. Measurements were performed using thermal ionisation mass spectrometry with a 50 Cr‐ 54 Cr 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‰ (2 s ). This comprehensive data set provides a valuable reference for quality assurance schemes and inter‐laboratory comparisons in Cr isotopic studies.