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Mineralogy and Iron Characterization of Plinthitic Soils on Alluvial Landforms in Venezuela
Author(s) -
Daugherty L. A.,
Arnold R. W.
Publication year - 1982
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/sssaj1982.03615995004600060025x
Subject(s) - ammonium oxalate , soil water , kaolinite , silt , clay minerals , goethite , hematite , gibbsite , geology , mineralogy , cation exchange capacity , eluvium , iron oxide , illite , chemistry , montmorillonite , environmental chemistry , soil science , inorganic chemistry , geomorphology , organic chemistry , adsorption
The iron oxides and clay mineralogy were characterized for several soils of Venezuela which contain plinthite and pseudo‐plinthite. Molar ratios of SiO 2 /Al 2 O 3 (Ki ratios) of the plinthite and pseudo‐plinthite zones range from below 2 to above 4 suggesting a wide range in mineral composition. Cation exchange capacity for these zones ranged from 14.6 to 65.6 meq/100 g of clay suggesting that these mottled zones are not always associated with low activity clays. Kaolinite dominated the clay minerals. Montmorillonite was identified in a few pedons. Goethite was the dominant iron oxide present in the plinthite. The percentage of iron was determined by extracting the soil with citrate‐bicarbonate‐dithionite and by extracting with ammonium oxalate. These two extractions were ratioed (OX/CBD) yielding values of >0.05 for pseudo‐plinthite and values of <0.05 for plinthite in most cases. Soils with plinthite contained most of the iron in the sand‐ and silt‐size fraction following one drying cycle while soils with pseudo‐plinthite contained most of the iron in the clay‐size fraction.