Finely divided hydrophobic silica and silicates are prepared by precipitating of alkali silicate solutions with mineral acids or metal salt solutions and treated with organohalosilanes. To the acid precipitation suspension recovered in known manner there is added as a hydrophobizing agent an organohalosilane, preferably at about 50.degree. to 90.degree. C., the precipitated product filtered, washed and dried and there subjected to a temperature of 300.degree. to 400.degree. C. There is used as the organohalosilane a prepolycondensed organohalosilane or a mixture of prepolycondensed organohalosilanes.