Abstract: Phyllosilicate minerals which exhibit in their structure, sequentially, octahedral layers containing magnesium, aluminum and/or iron oxides and tetrahedral layers of silica, are superficially etched with dilute acid to remove the outer octahedral layer under controlled conditions which preserve the basic structural integrity of the mineral substance. The acid etch exposes silanol groups on the outer silicate layer of the mineral so that they become available to form silicon-to-oxygen-to-silicon-to-carbon bonds through condensation with organo-silanes. The condensation of the organo-silane with the conditioned mineral surface is accomplished by mixing the acid etched silicate mineral with the organo-silane in a suitable solvent system under mild conditions.The organo-silane may be chosen from either of two classes: those which impart an oleophilic surface to the mineral; or those which enable the mineral surface to form additional chemical bonds with reactive sites within certain polymers and prepolymers.