A Mössbauer study of the weathering of hornblende

Abstract The behaviour of iron in the natural weathering of hornblende in a sedentary soil profile has been investigated using the Mòssbauer effect. The spectra from samples at different stages of weathering show appreciable differences which can be accounted for if ferrous iron is lost preferentially from M(3) sites where it is coordinated to hydroxyl groups in a trans arrangement. Unlike biotite the proportion of ferric iron does not increase during weathering and this illustrates the difficulty with which the ferrous iron is oxidized in the amphibole structure.