In Scandinavian podzols a swelling dioctahedral mineral, probably derived from dioctahedral mica and iron-rich chlorite, has been found in the clay (<2µ) fractions from A2-horizons. This mineral, or group of minerals, is shown by X-ray examination and differential thermal analysis to be of a vermiculite-smectite type, thus making the differentiation between vermiculite and smectite still more problematical. The pretreatment of the samples and choice of interlayer cations is shown to be of great significance for the identification of soil clay minerals.