Mossbauer studies of subfossil oak

Subfossil oak wood found in a dried-up bog in Bavaria, Germany, was studied by Mossbauer spectroscopy. The bog oaks contain substantial amounts of iron taken up from the bog waters and presumably forming complexes with the tanning agents in the oak wood. The iron is mainly Fe3+ and much of this exhibits an uncommonly large quadrupole splitting of up to 1.6 mm/s that can tentatively be explained by the formation of oxo-bridged iron dimers. Only rarely, mainly in the dense wood of the roots of bog oaks, was divalent iron found. When the wood was ground to a powder the divalent iron oxidized to Fe3+ within hours. This suggests that iron is taken up from the bog water as Fe2+ and oxidizes only when the wood emerges from the water and comes into contact with air.