 In contrast, basalt and gabbro in non-arc settings typically record oxygen fugacities from about those of the FMQ buffer to a log unit or so more reducing than that buffer.Oxidizing conditions are common in some environments of deposition and diagenesis of sedimentary rocks.The fugacity of oxygen at the MH buffer (magnetite-hematite) is only about 10−70 at 25 °C, but it is about 0.2 atmospheres in the Earth's atmosphere, so some sedimentary environments are far more oxidizing than those in magmas.