Clay mineral assemblages present within the coals and coal-bearing strata of the Wabamun area of the central Alberta Plains are a product of the original peat-accumulating and adjacent fluvial depositional environments. In the Highvale area, acidic conditions promoted by the accumulation and humification of thick peats were conducive to the diagenetic mineralization of kaolinite from parent volcanic ash. Detrital minerals are few, and the presence of cristobalite is evidence that dissolution processes were active. Volcanic ash horizons from adjacent environments at Whitewood and Genesee, which were under a greater influence of fluvial activity and fresh water, are composed predominantly of smectite and display a diversity of detrital minerals.