A method for producing a precipitated silicon dioxide having a new combination of physical and chemical properties is disclosed. The pigments are produced by acidulating a solution of an alkali metal silicate with an acid under controlled precipitation conditions. The aqueous reaction medium comprising the precipitated silica is then post-conditioned by introducing a second silicate solution into the reaction vessel and thereafter adding additional acid to react with the said second silicate solution. By varying the amount of the silicate employed in the post-conditioning step, a product is obtained which has a unique combination of physical and chemical properties including reduced wet cake moisture content, high surface areas and oil absorptions, improved surface activity, friability, wetting characteristics, and the like. The product has particular utility for use as a rubber reinforcing agent because of its increased surface activity and oil absorption, etc. The product, however, may be used in paints, paper, detergents, dentifrice compositions, molecular sieves, and polymeric compositions. An unexpected discovery of the invention involves the production of a rubber reinforcing silica which has a decreased wet cake moisture content. In one particularly advantageous embodiment, an adduct material, such as aluminum, is added to control the refractive index and surface area of the product.