Iron oxides, among the many other earth-abundant mineral oxides, have been closely involved in the origin and evolution of life on Earth. Naturally, they occur as polymorphic mineral oxides and can show a rich structural anisotropy. This inherently enables them to demonstrate a wide range of physical and chemical properties. Also, their interaction with broad-spectrum sunlight is of significance to various geochemical and industrial processes. Recently, the hematite (α-Fe₂O₃) and magnetite (Fe₃O₄) are being considered again as a potential catalyst for industrial photocatalysis.