A method for preparing a novel hydrogel including silico-metallic mineral particles of the formula (Six(Si-A)1−x)4M3O11.n′H2O, in which: x is a real number in the range [0.75; 1], A denotes a group selected from methyl and hydrocarbon groups including at least one heteroatom, and M is a metal selected from the group consisting of magnesium, cobalt, zinc, copper, manganese, iron, nickel and chromium, wherein a coprecipitation reaction is carried out in an aqueous medium between: at least one metal salt of the metal M, sodium metasilicate, Na2OSiO2, and at least one water-soluble oxysilane of formula (I): in which R1, R2 and R3 are selected from hydrogen and linear alkyl groups including 1 to 3 carbon atoms.