Pedogenic iron oxides (Fe d) were quantified in 22 hematitic and goethitic soil samples (19 from oxic horizons; one from a plinthic horizon; one from a cambic horizon; one from saprolite) by use of two extraction procedures with sodium dithionite-citrate-bicarbonate (DCB). Approximately ninety percent of the Fe d content was extracted at the first extraction by the DCB80 procedure. This procedure was more effective at extracting Fe d than the DCB20, whose efficiency decreased with increasing Al3+-substitution in goethite. Compared with the DRX analysis, Al3+-substitution in goethite determined by the DCB80 procedure was superestimated. Maghemite masked Al3+-substitution estimates in hematite from hematitic samples.
iron extraction; sodium dithionite; aluminum substitution
