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Clay Minerals; June 2008; v. 43; no. 2; p. 185-193; DOI: 10.1180/claymin.2008.043.2.03
© 2008 Mineralogical Society of Great Britain and Ireland
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Research Paper

Vermiculite, with hydroxy-aluminium interlayer, and kaolinite formation in a subtropical sandy soil from south Brazil

E. C. Bortoluzzi1, B. Velde2, M. Pernes3, J. C. Dur3 and D. Tessier3,*

1 Faculdade de Agronomia e Medicina Veterinária, Fundação Universidade de Passo Fundo (FAMV-FUPF), 611, 99051-000 Passo Fundo, Rio Grande do Sul, Brazil, 2 Département de Géologie, Ecole Normale Supérieure, 24 rue Lhomond, 75231 Paris – Cedex 05, France, and 3 Institut National de la Recherche Agronomique (INRA), Unité PESSAC, Route de Saint-Cyr, 78026 Versailles Cedex, France

* E-mail: daniel.tessier{at}wanadoo.fr

(Received 19 March 2007; revised 6 November 2007)

The purpose of this study was to investigate the clay mineral phases in a Rhodic Acrisol soil and to discuss their evolution in subtropical conditions. Prairie and forest soil profiles were sampled and clay fractions of the parent material and soil horizons analysed by X-ray diffraction (XRD) at the Federal University of Santa Maria, Rio Grande do Sul-Brazil. The XRD results show the presence of interstratified kaolinite-smectite and illite-smectite as well as illite in the parent material. These minerals were also found in the soil samples but with two new phases: hydroxy-aluminium interlayered vermiculite (HIV), which showed incomplete collapse with treatment at 550°C, and a newly formed kaolinite (d = 7.17 Å). Under a subtropical climate and a sandy lithology, HIV and kaolinite appear to be a result of a specific pedogenic clay formation, related to the natural vegetation. Originally, under the prairie area, the intensity of the weathering processes was weak (within 2:1 clay minerals), as only small quantities of kaolinite and Fe oxides, and no evidence of gibbsite, were found.

KEYWORDS: hydroxy-Al interlayer, soil genesis, particle-size distribution, sandy soils, XRD, Brazil






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