The tepetates of Mexico Highlands are indurated horizons with fragipan pr0perties. Tepetates appear among pyroclastic deposits (T1, T2, T3). A soil profile located near Texcoco, Mexico, including tepetate layers was studied. Mineralogical and microscopical features of this profile were studied using a series of methods. This report the main results of the study. Tepetates were characterized by several features: first, the nature of their parent material; second, a close matrix microstructure and third, their colloidal fraction. The latter is conformed mainly by laminated 1:1 to 2:1 mixed layer minerals made of flaky layers. These features can explain the fragipan properties of tepetates and most of their mechanical behaviour. (Résumé d'auteur)
