A solid hydrocarbon-insoluble, alpha-olefin polymerization catalyst component with superior activity, stereospecificity and morphology characteristics comprises the product formed by (A) forming a solution of a magnesium-containing species from a magnesium carbonate or a magnesium carboxylate; (B) precipitating solid particles from such magnesium-containing solution by treatment with a transition metal halide and an organosilane; (C) reprecipitating such solid particles from a mixture containing a cyclic ether; and (D) treating the reprecipitated particles with a transition metal compound and an electron donor.