The invention relates to a crystallized solid, referred to by the name IM-12, which exhibits an x-ray diffraction diagram as provided below. Said solid exhibits a chemical composition that is expressed on an anhydrous base, in terms of oxide moles, by the formula XO.sub.2:m YO.sub.2:p Z.sub.2O.sub.3:q R.sub.2/nO, where R represents one or more cation(s) of valence n, X represents one or more different tetravalent element(s) of germanium, Y represents germanium, and Z represents at least one trivalent element.