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Clay Minerals; December 2007; v. 42; no. 4; p. 437-451; DOI: 10.1180/claymin.2007.042.4.02
© 2007 Mineralogical Society of Great Britain and Ireland
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Research Paper

Iron oxides in tropical soils on various parent materials

W. WIRIYAKITNATEEKUL1,2, A. SUDDHIPRAKARN2,*, I. KHEORUENROMNE2, M. N. SMIRK3 and R. J. GILKES3

1 Office of Science for Land Development, Land Development Department, Chatuchak, Bangkok 10900, Thailand, 2 Department of Soil Science, Faculty of Agriculture, Kasetsart University, Bangkok 10900, Thailand, and 3 School of Earth and Geographical Sciences, Faculty of Natural and Agricultural Sciences, University of Western Australia, Crawley, WA 6009, Australia

* E-mail: agrals{at}ku.ac.th

(Received 26 May 2007; revised 8 July 2007)

Twenty nine Fe oxide concentrates of Thai soils formed on basalt, sandstone, shale/limestone and granite were investigated. Goethite and hematite are relatively more abundant in granitic and basaltic soils, respectively. Values of Feo/Fed range from 0.01 to 0.28 indicating that free Fe oxides are mostly crystalline.

There are no systematic differences in unit-cell dimensions for goethite and hematite in soils on different parent materials. Mean crystallite dimensions calculated from the 110 reflections are greater for hematite than for goethite. Aluminium substitution varies from 8 to 24 mole% for goethite and from 4 to 17 mole% for hematite. The dehydroxylation temperature for goethite ranges from 285°C to 320°C. The goethite in basaltic soils has a smaller crystal size and Al substitution, as well as a lower dehydroxylation temperature, compared to soils on other parent materials. The dehydroxylation temperature of goethite is positively related to Al substitution (R = +0.58), MCD110 (R = +0.49) and Ald (R = +0.53). The Mn, Ni, Cr, V and P in these soils occur in Fe oxides rather than as discrete minerals.

KEYWORDS: goethite, hematite, iron, aluminium, tropical soil, parent material






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