Abstract: Amorphous, approximately spherical silica particles prepared by the acidic hydrolysis of an approximately spherical synthetic calcium silicate having a uniform microgranular structure on their external surfaces and a structure in the interior thereof which structure only weakly recall the original crystal needle structure of the starting material. The average external particle size is from 15 to 80 .mu.m, the apparent particle volume is from 1.3 to 3 cm.sup.3 /g, and the specific surface area is from 250 to 800 m.sup.2 /g. The silica particles are particularly suitable for use as catalyst supports.