Two New Potential Apatite Reference Materials for <i>In Situ</i> Sr‐Nd Isotope Measurement

Apatite supergroup minerals are common in diverse lithologies and rich in strontium and neodymium making them optimal minerals for in situ Sr‐Nd isotopic tracing in geological studies. We present detailed spectroscopy, major and trace element compositional determinations, and Sr‐Nd isotopic measurement results for two natural apatite samples (MAP‐1 and MAP‐4) to assess their chemical homogeneity and suitability as Sr and Sm‐Nd reference materials (RMs). The results reveal that both samples display remarkably uniform trace element distributions, and nearly consistent major element chemistry and Sr‐Nd isotope ratios. They are particularly characterised by high Sr mass fractions (&gt; 8000 μg g ‐1 ) and relatively high Nd mass fractions (~ 3000 μg g ‐1 ). For MAP‐1, the 87 Sr/ 86 Sr and 143 Nd/ 144 Nd values determined by (ID‐)TIMS are 0.704340 ± 0.000029 (2 s , n = 3) and 0.511978 ± 0.000008 (2 s , n = 3). MAP‐4 yielded 87 Sr/ 86 Sr of 0.704354 ± 0.000010 (2 s , n = 4) and 143 Nd/ 144 Nd of 0.511956 ± 0.000005 (2 s , n = 7). Reproducibility tests using LA‐MC‐ICP‐MS were consistent or nearly consistent with the results of (ID‐)TIMS measurements, demonstrating that both fluorapatites are suitable new RMs for in situ 87 Sr/ 86 Sr and 143 Nd/ 144 Nd isotopic measurements, providing new benchmarks of apatite RMs for laser‐based Sr‐Nd isotopic measurements.