Mössbauer Spectroscopy of Selected Banded Iron Formations

Banded iron formations are rocks of sedimentary origin, formed 2-4 billion years ago. They consist of alternating layers of iron oxides and silicates. In the oxide layers the iron is often in the Fe3+ state while in the silicate layers the iron is mainly in the Fe2+ state. The conditions under which banded iron formations formed are not understood, but the varying oxidation states of iron reflect somehow the evolution of the terrestrial atmosphere. The oxidation state of iron in selected banded iron formations has been determined by Mössbauer spectroscopy. It is found that the youngest rocks are the most oxidized.