Abstract: An aqueous slurry according to the invention comprises (a) a crystalline aluminosilicate represented by the empirical formula M2/nO.Al2O3.xSiO2.yH2O wherein M represents a first metal moiety, said first metal having a valency of n, x indicates the ratio of molecules of silica to molecules of alumina and y indicates the ratio of molecules of water to molecules of alumina, (b) a salt of a second metal selected from the group consisting of Group III metals, metallic elements of Group IV, magnesium, titanium, chromium, iron, nickel, copper, zinc, zirconium and silver, said salt of a second metal being present in an amount which is sufficient to replace from about 2.0 to about 40 per cent by weight of the first metal moiety, and (c) particulate silica having a BET surface area greater than 500 m2/g and a pore volume, as measured by nitrogen manometry of less than 2.1 cm3/g. The slurry is stable on storage but has a low viscosity at low shear rate.