High‐Mg# Olivine, Clinopyroxene and Orthopyroxene Reference Materials for In Situ Oxygen Isotope Determination

Secondary ion mass spectrometry (SIMS) requires matrix‐matched reference materials to calibrate mass fractionation during oxygen isotope measurement. Over one thousand SIMS oxygen isotope measurements were conducted on eleven natural mineral samples (five olivines, three clinopyroxenes and three orthopyroxenes) in nineteen sessions using CAMECA IMS 1280 SIMS instruments to evaluate their potential as SIMS reference materials. The obtained results reveal oxygen isotope homogeneity of these samples. No matrix effect was measured for the same variety of mineral samples with limited Mg‐number variations (89.6–94.2, 90–91.9 and 90.1–92.1 for olivine, clinopyroxene and orthopyroxene, respectively). The recommended oxygen isotope compositions of these samples were determined using laser fluorination. These samples are therefore suitable to be used as reference materials for in situ oxygen isotope microanalysis. Key Points We suggest five olivine, three clinopyroxene and three orthopyroxene SIMS reference materials for oxygen isotope analysis. Mg‐number variations are 89.6–94.2, 90–91.9 and 90.1–92.1 for olivine, clinopyroxene and orthopyroxene, respectively. The recommended oxygen isotope compositions were determined using the laser fluorination method.