A mössbauer spectroscopic study of New Zealand soils and soil concretions

Abstract

The occurrence of iron in twenty four natural samples was studied using Mössbauer spectroscopy. The samples included whole soils, soil concretions, the soils surrounding the concretions and a ferric gel. Identification of the iron minerals was made, attention being concentrated on the secondary oxides and oxyhydroxides. The use of Mössbauer spectroscopy also enabled these minerals to be quantitatively determined. Akaganeite (β-iron(III) oxide hydroxide), present in significant quantities, was found to be of widespread occurrence. Goethite (α-FeOOH), of particle size less than ~100°A, was found to be the other major iron mineral in New Zealand soils; with little goethite of sufficient crystallinity to exhibit magnetic hyperfine splitting, being detected. Hematite (α-Fe2O3) occurrence was found to be limited. The occurrence of these secondary iron oxides and oxyhydroxides is discussed with reference to weathering processes. Mössbauer spectroscopy has been shown to provide detailed information on naturally occurring iron minerals. Identification and a quantitative measure can be made of these often amorphous soil constituents. Some of the results arising from this research have been published (see Appendix 6).