The rate of acid dissolution in HCl is a common method for differentiating various phases of Fe in clay samples. A readily soluble Fe phase, denoted herein as the RS phase, is often observed in bentonite, but its identity has yet to be established. Seven Czech bentonites were studied by acid dissolution in 6 M HCl and by Mössbauer spectroscopy. A highly-soluble Fe phase was found in the <2-µm fractions of all seven Czech bentonites, ranging from 15 % to 67 % of total Fe. In all seven samples, Mössbauer spectroscopy revealed a goethite phase; in six, the goethite phase correlated well with the amount of RS Fe. In the seventh sample, Hroznetin, Fe(II) identified by both chemical analysis (phenanthroline method) and Mössbauer spectroscopy was the main source of RS Fe.