The < 2 µm fraction separated from Stebno (near Usti nad Labem, Czecho-Slovakia) bentonite contains 17.59 % Fe₂0₃. A mineralogical and crystallochemical study using X-ray diffraction, thermal analysis, infrared and Mössbauer spectroscopies and acid dissolution showed that the main mineral is an iron-rich beidellite (Fe-beidellite) with an unusually low dehydroxylation temperature (510 °C),having about equal amounts of aluminium and iron in the octahedral sites. Minor amounts of anatase and kaolinite (both below 3 %) were also identified in this fraction. About 79 % of total iron present in the sample is bound in smectite and the remaining 21 % is in goethite.