Iron Oxides

Abstract

Oxygen and iron are the most and the fourth most abundant elements by mass in the earth’s crust, in which their respective proportions amount to 46.6 and 5.0 percent. It is therefore not surprising that compounds made up of these two elements are common in nature. The oxides, oxyhydroxides and a (single) hydroxide of trivalent iron are often grouped together under the general term “iron oxides”, and the occurrence of nine such iron oxides sensu lato has so far been registered in materials formed on the earth’s surface. As Schwertmann and Taylor (1989) put it “The iron oxides ... are present in most soils of the different climatic regions in one or more of their mineral forms and at variable levels of concentration”. The same is true for many sediments, the other major group of materials formed in the weathering environment.