Characterization of Hydroxy-Interlayered Vermiculite and Illite/Smectite Interstratified Minerals from the Weathering of Chlorite in a Cryorthod

Dominique Righi1, Sabine Petit1 and Alain Bouchet2
1 UA 721, CNRS, Laboratoires de Pédologie et Pétrologie de la Surface, Faculté des Sciences, 86022 Poitiers-Cedex, France
2 ERM, Mérovée, BP25, 86320 Civaux, France

Abstract: X-ray diffraction, FTIR, and chemical analyses were performed on clay fractions (1–2 µm, <0.1 µm), separated by means of size fractionations and high-gradient magnetic separation techniques, from a Cryorthod developed in a chlorite-mica schist saprolite. Weathering of large phyllosilicates pre-existing in the saprolite involves physical fragmentation and mineralogical transformations. Chloritic minerals in the coarse fractions were the most affected by physical breakdown, while micas were generally preserved. As a consequence, a concentration of mica layers occurred in the coarse clay fraction, while chloritic residues accumulated in the fine clays. These residues exhibited the typical XRD pattern of hydroxy-interlayered intergrade minerals, but the interlayered contaminants were found to be mainly hydroxy-Mg cations. Further mineralogical transformations of the intergrade minerals involved the progressive removal of the hydroxide interlayered sheet and dissolution of chloritic layers. Illite/smectite mixed-layers were formed in the surface horizon of the soil profile. These processes were associated with a strong decrease in Fe and Mg contents in the clay fractions.

Key Words: Chlorite • Hydroxy-interlayered intergrades • Illite/smectite mixed-layers • Soil clays • Spodosol

Clays and Clay Minerals; August 1993 v. 41; no. 4; p. 484-495; DOI: 10.1346/CCMN.1993.0410409
© 1993, The Clay Minerals Society
Clay Minerals Society (www.clays.org)