Iron Oxides Exhibit Greater Complexity

Researchers have synthesized a new iron oxide, Fe₅O₆, adding to evidence that the two most abundant elements on Earth form a complex chemical system that has been previously unrecognized (Sci. Adv. 2015, DOI: 10.1126/sciadv.1400260). Iron oxides play a major role in the redox chemistry of rocks, particularly deep in the interior of Earth, and possibly other planets. Until recently, scientists believed iron oxides came in three forms: FeO, Fe₂O₃, and Fe₃O₄. In 2011, Barbara Lavina at the University of Nevada, Las Vegas, and Yue Meng at the Carnegie Institution of Washington, Argonne, Ill., upended that belief with their synthesis of Fe₄O₅ (Proc. Natl. Acad. Sci. USA, 2011, DOI: 10.1073/pnas.1107573108). Lavina and Meng have now identified Fe₅O₆ from mixtures of iron and hematite, which they heated and pressurized in the laboratory. “Fe₅O₆ and Fe₄O₅ are plausible new players in Earth’s mantle redox equilibria,” the authors note.