Oxidation State of Iron in Glauconite from Oxidized and Reduced Zones of Soil-Geologic Columns1

D. S. Fanning, M. C. Rabenhorst, Leopold May and D. P. Wagner
Department of Agronomy, University of Maryland, College Park, Maryland 20742
Department of Chemistry, The Catholic University of America, Washington, D.C. 20064
Geo-Sci Consultants, Inc., College Park, Maryland 20740
1 Contribution 7756 and Scientific Article A-4753 of Maryland Agricultural Experiment Station, Department of Agronomy, College Park, Maryland 20742.

Abstract: Glauconite from the oxidized and reduced zones of soil-geologic columns at two Coastal Plain sites, one in Maryland and one in New Jersey, was examined by Mössbauer spectroscopy. The data indicate that glauconite in the reduced zones had a higher proportion of its structural iron in the ferrous, as opposed to the ferric state. The Fe2+/Fe3+ ratio ranged from 0 to 0.2 for the glauconite from the oxidized zone and was about 0.35 for the glauconite in the reduced zones. Despite the presence of pyrite in the reduced zone, which might be expected to make ferric iron unstable because of the presence of sulfide S, about 75% of the Fe in the glauconite in the reduced zone was in the ferric state. Thin section analysis showed some glauconite in the reduced zones to be intimately associated with pyrite and some aggregates of fine pyrite crystals were locally present in cracks in glauconite pellets. In the oxidized zones, pyrite was absent and the glauconite was more yellow under plane-polarized light, as opposed to more green for the glauconite in the reduced zones. These data indicate that reports of studies of glauconite should stipulate whether samples are from the oxidized or reduced zone of soil-geologic columns.

Key Words: Glauconite • Iron • Mössbauer spectroscopy • Oxidized zone • Pyrite • Reduced zone • Soil

Clays and Clay Minerals; February 1989 v. 37; no. 1; p. 59-64; DOI: 10.1346/CCMN.1989.0370107
© 1989, The Clay Minerals Society
Clay Minerals Society (www.clays.org)