The invention provides a chemical-mechanical polishing composition comprising: (a) silica particles, (b) about 5×10−3 to about 10 millimoles per kilogram of at least one alkaline earth metal selected from the group consisting of calcium, strontium, barium, and mixtures thereof, based on the total weight of the polishing composition, (c) about 0.1 to about 15 wt. % of an oxidizing agent, and (d) a liquid carrier comprising water. The invention also provides a polishing composition, which optionally comprises an oxidizing agent, comprising about 5×10−3 to about 10 millimoles per kilogram of at least one alkaline earth metal selected from the group consisting of calcium, strontium, and mixtures thereof. The invention further provides methods for polishing a substrate using the aforementioned polishing compositions.