Patent ID: 7887714

Claim:
An abrasive for polishing a rock crystal, a quartz glass for a photomask, a semiconductor device or a hard disk made of glass, the abrasive comprising a sol, which includes particles dispersed in an aqueous medium, wherein: the particles comprise as a main component crystalline cerium oxide of cubic system and as an additional component a lanthanum compound, neodymium compound or a combination thereof; the additional component is contained in an X/(Ce+X) molar ratio of 0.005 to 0.15 in which X is lanthanum atoms, neodymium atoms or a combination thereof; the particles are present in the abrasive in an amount of 0.1 to 50 wt %; the particles have a particle size of 50 to 150 nm; the particles have a specific surface area of 2 to 200 m 2 /g; and the abrasive has a pH of 3 to 4.6.