Oxygen Isotopic Compositions of San Carlos Olivine Standard NMNH 111312–42

San Carlos olivine geostandard developed by Gene Jarosewich and co-workers at the Smithsonian Institution, named NMNH 111312–44, was the most widespread olivine geostandard used in olivine oxygen isotopic determination. However, the NMNH 111312–44 olivine grains have run out completely. Another set of San Carlos olivine, whose grains are larger, named NMNH 111312–42, was distributed by the Smithsonian Institution. Whether they have the same oxygen isotopic composition is still unclear. This study analyzed the oxygen isotopic compositions of NMNH 111312–42 and NMNH 111312–44, using a CAMECA IMS–1280 secondary ion mass spectrometer. The results show that NMNH 111312–42 (5.28 ± 0.17‰, 1SD, N = 35) and NMNH 111312–44 (5.22 ± 0.16‰, 1SD, N = 29) olivine grains have indistinguishable δ18O values within analytical error, suggesting that NMNH 111312–42 olivine grains can be taken as the same geostandard as NMNH 111312–44 olivine grains for high-precision oxygen isotope analysis.