NWA 16813 (CK6) Records Almost Highest Oxygen Fugacity in Meteorites

Abstract Magnetite-ilmenite pairs in meteorites serve as reliable thermometers and oxygen fugacity (fO 2 ) indicators for constraining both nebular conditions and thermal metamorphic histories. While CK and CV chondrites exhibit nearly identical petrological characteristics and oxygen isotope compositions, our analysis of NWA 16813 reveals it records the highest fO 2 (log fO 2 = −20.51 (589.34°C) − log fO 2 = −14.21 (608.63°C)) yet measured among these meteorites. This finding provides critical evidence that CK and CV chondrites experienced fundamentally different redox conditions during their formation. The fO 2 data from NWA 16813, combined with its distinct petrological and mineralogical features, strongly suggest that CK and CV chondrites originated from chemically separate reservoirs in the protoplanetary disk despite their apparent similarities.