Pyrogenically produced silicon dioxide powder in the form of aggregates of primary particles having a BET surface area of 150.+-.15 m.sup.2/g, wherein the aggregates display an average surface area of 12000 to 20000 nm.sup.2, an average equivalent circle diameter (ECD) of 90 to 120 nm and an average circumference of 1150 to 1700 nm. It is produced by a pyrogenic process in which silicon tetrachloride and a second silicon component comprising H.sub.3SiCl, H.sub.2SiCl.sub.2, HSiCl.sub.3, CH.sub.3SiCl.sub.3, (CH.sub.3).sub.2SiCl.sub.2, (CH.sub.3).sub.3SiCl and/or (n-C.sub.3H.sub.7)SiCl.sub.3 are mixed with primary air and a combustion gas and burnt into a reaction chamber, secondary air also being introduced into the reaction chamber, and the feed materials being chosen such that an adiabatic flame temperature of 1670 to 1730.degree. C. is obtained. Silicone sealing compound containing the pyrogenically produced silicon dioxide powder.