Stable, thick poly(dimethylsiloxane) (PDMS) coatings are formed on iron(III) and aluminum oxide and calcium carbonate particles by impregnating the particles with dimethylsilicone oil and heating at 250-280 degrees C. These coatings are strongly resistant to solvent extraction and to exposure in a water-saturated atmosphere. Coated particles are strongly hydrophobic, as evidenced by their greater stability in apolar solvents. Silicone coating formation on oxide particles is interpreted as a result of two reactions: siloxane chain opening at higher temperatures, followed by the reaction of active chain end-groups with hydroxo groups at the metal oxide or carbonate surfaces and silicone cross-linking by methylene or siloxane bridges. The procedures described in this paper differ from usual silanization or siliconization procedures because it uses stable PDMS and yields thicker coatings. (C) 1996 John Wiley & Sons, Inc.601120012006