Probing iron redox state in multicomponent glasses by XPS

► XPS proves to be a useful and effective tool in determination of iron redox state in basalt glasses. ► XPS is found to be a suitable tool for determining local fluctuations in the redox state of polyvalent elements. ► It is confirmed that the oxidation state of iron shifts towards the reduced state in basalt glasses when the melting temperature is increased. ► The results imply a similar equilibrium ferric iron fraction exists for any glass system.