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Iron Oxide Mineralogy of Well‐drained Ultisols and Oxisols: II. Influence on Color, Surface Area, and Phosphate Retention
Author(s) -
Bigham J. M.,
Golden D. C.,
Buol S. W.,
Weed S. B.,
Bowen L. H.
Publication year - 1978
Publication title -
soil science society of america journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.836
H-Index - 168
eISSN - 1435-0661
pISSN - 0361-5995
DOI - 10.2136/sssaj1978.03615995004200050034x
Subject(s) - hematite , goethite , ultisol , oxisol , maghemite , iron oxide , mineralogy , subsoil , soil water , chemistry , kaolinite , clay minerals , magnetite , geology , soil science , paleontology , organic chemistry , adsorption
Subsoil samples from selected North Carolina Ultisols and Brazilian Oxisols were analyzed to determine how the colors of these materials were influenced by the nature and distribution of their constituent iron oxides. The effects of extraneous variables, i.e., other than the iron oxides, were minimized by utilizing pairs of red and yellow soils that were otherwise similar in their physical, morphological, and mineralogical properties. The iron oxides were found to be concentrated in the <0.2‐µm fractions, and the colors of these clays were the same as or similar to those of the parent soils. The spectral properties of the <0.2‐µm clays were primarily influenced by iron mineralogy. Goethite or mixtures of goethite and hematite were identified in all of the clays; however, Mössbauer analyses indicated that the red members of all sample pairs contained larger proportions of hematite than did their yellow counterparts. In addition, as the clays became redder in hue, the ratio of hematite to goethite generally increased. Calculated surface areas for the iron oxides ranged from 60 to 200 m 2 /g; values from the yellow clays were consistently higher than those obtained from their red counterparts. The yellow clays were also more efficient adsorbers of phosphate.