Abstract: Randomly interstratified clay in synthesized by:(i) saturating (replacing all the exchangeable cations of) a first clay with alkali metal ions (preferably Na.sup.+ or Li.sup.+), removing any excess alkali metal ions, and forming the saturated clay into a suspension containing no suspended particles exceeding 10.sup.-7 m equivalent spherical diameter,(ii) saturating a second clay with alkali metal ions (preferably Na.sup.+ or Li.sup.+), removing any excess alkali metal ions, and forming the saturated clay into a suspension containing no suspended particles exceeding 10.sup.-7 m equivalent spherical diameter,(iii) mixing the suspensions from (i) and (ii) to form a mixed suspension, and(iv) sedimenting and optionally drying the mixed suspension, the sediment being the synthetic randomly interstratified clay.A wider range of synthetic clay compositions is thereby made available for use as catalysts, sorbents etc.