Disclosed are flocced mineral materials which may be utilized to prepare high temperature resistant, water resistant articles. These materials are prepared by utilizing, as a starting material, a gellable layered swelled silicate that has an average charge per structural unit that ranges from about -0.5 to -1 and which contains interstitial cations which promote swelling with a source of at least one species of an exchange cation that is derived from guanidine or compounds closely related thereto.