The present invention relates to sheet silicate lamellae of a 2:1 sheet silicate with a high aspect ratio, to a method for producing these sheet silicate lamellae and to an aqueous dispersion which comprises the sheet silicate lamellae. The present invention further relates to the use of the sheet silicate lamellae of the invention for producing a composite material, and also to a corresponding composite material comprising or obtainable using the sheet silicate lamellae, more particularly for use as a diffusion barrier or as a flame retardant.