Abstract: The present invention provides the amorphous silica particles having a double structure of a core of the dense amorphous silica and a shell of the bulky amorphous silica, having a volume-based median diameter of from 1 to 5 &mgr;m and containing not more than 10% by volume of fine particles having a particle diameter of not larger than 0.5 &mgr;m. The amorphous silica particles of the double structure have constant particle diameters not only in the powdery state but also in a state where they are blended in a coating material or in a resin, without developing fine particles, exhibit excellent delustering action and antiblocking action, exhibit decreased abrading property, and exhibit excellent resistance against scars or abrasion.

Abstract: The present invention provides the amorphous silica particles having a double structure of a core of the dense amorphous silica and a shell of the bulky amorphous silica, having a volume-based median diameter of from 1 to 5 .mu.m and containing not more than 10% by volume of fine particles having a particle diameter of not larger than 0.5 .mu.m. The amorphous silica particles of the double structure have constant particle diameters not only in the powdery state but also in a state where they are blended in a coating material or in a resin, without developing fine particles, exhibit excellent delustering action and antiblocking action, exhibit decreased abrading property, and exhibit excellent resistance against scars or abrasion.

Abstract: A novel olefin polymerization catalyst is obtained by contacting the following components (1) to (5) with one another: (1) a compound represented by the general formula Me.sup.1 R.sup.1.sub.p (OR.sup.2).sub.q X.sup.1.sub.4-p-q, (2) a compound represented by the general formula Me.sup.2 R.sup.3.sub.m (OR.sup.4).sub.n X.sup.2.sub.z-m-n, (3) an organocyclic compound having conjugated double bonds; (4) a modified organoaluminum compound having Al--O--Al bond(s); and (5) a silicon oxide and/or an aluminum oxide both having characteristic average particle diameter, specific surface area, volume of pores ranging in pore radius from 18 to 1,000 Angstroms, apparent specific gravity not lower than 0.32, and proportion of 50 .mu.m or smaller particles.