New deposits of saponite have been described recently in the Madrid Basin (Madrid and Toledo provinces, Central Spain), a zone very rich in Mg silicates, especially in sepiolite. This is the first time that the high surface area saponitic material from Yunclillos deposit (Toledo province) is described. The acid treatment of this material with diluted solutions of HCl (0.62 and 1.25% by weight) at 25 degrees C for 2, 6, 24, and 48 h has been carried out. Although the conditions employed in the leaching are very soft, most of the octahedral sheet of the clay is dissolved, as indicated by the high removal of Mg cations and corroborated by the changes observed in the FT-IR spectra and by the simplification in the profile of the TGA-DTA curves of the solids obtained after the treatments. The destruction of the saponite structure by the treatments results in the generation of free silica. The surface area of natural saponite (161 m(2) g(-1)) is doubled in the leached solids, even under the mild conditions considered, reaching a maximum value of 392 m(2) g(-1). The texture of the free silica generated after the saponite ordered structure affects the properties of the activated solids, as shown by the numerical analyses of the nitrogen adsorption-desorption isotherms of these solids, mainly made by using the "t" and "f" plots.