The evolution of the electron delocalization in the ferrous subspectra in a sample of mixed valence ferrous-ferric freudenbergite has been followed by Mossbauer spectroscopy from 6 K to 650 K. The spectral changes do not involve the ferric component, leading to the conclusion that it is due to a thermally driven delocalization of the sixth d-electron on the ferrous ions. The phenomenon does not occur in samples of pure ferrous freudenbergite.