Twelve cationic, amine-salt silica-collectors were evaluated on three samples of magnetic iron-ore concentrate. Coco primary amine acetate was used as the standard of comparison. Lauryl primary amine acetate is somewhat more efficient in collecting silica than the standard, and equally selective. Tallow primary amine acetate is equally selective and somewhat less efficient than the the standard. Coco diamine is more selective and somewhat more efficient than the standard. Oleyl and tallow diamines are more selective and somewhat less efficient than the standard. Trimethyl alkyl ammonium chloride compounds are more selective but less efficient than primary amines and diamines. Selectivity, in general, is inversely proportional to efficiency (silica pulling strength). Strong collectors, in other words, tend to float small amounts of iron along with the silica. Finely ground (90% less than 325 mesh or finer) magnetic concentrates with iron and silica almost completely liberated are highly responsive to upgrading. Concentrates of the same fine mesh size but containing unliberated iron-silicate are less responsive.