A polishing slurry, useful in optical or CMP applications, comprises a ceria with a BET surface area of at least 10 m2/gm. The slurry may be made by subjecting a commercial ceria slurry comprising agglomerates to a mechano-chemical treatment at a pH of from 9 to 11 using media that are low purity alpha alumina or zirconia. Preferred slurries maintain a positive surface charge at all pH values. CMP slurries preferably comprise in addition an anionic surfactant to aid in removal of surface residues.