Described is a process for the preparation of a crystallised lamellar solid formed by magadiite consisting of implementing in a step (i) mixing of at least one silica source, at least one salt of N,N,N′,N′-tetramethyl-N,N′-dibenzyloctanediammonium, at least one alkali and/or alkaline earth metal M and water and then implementing in a step (ii) hydrothermal treatment of said mixture until said crystallised lamellar solid constituted by magadiite is formed.