 Iron, sulfur, and manganese are three of the relatively abundant elements in the Earth's crust that occur in more than one oxidation state.For instance, iron, the fourth most abundant element in the crust, exists as native iron, ferrous iron (Fe2+), and ferric iron (Fe3+).The redox state of a rock affects the relative proportions of the oxidation states of these elements and hence may determine both the minerals present and their compositions.