Microsilica, also known as silica fume or condensed silica fume, is an ultra-fine, high-purity amorphous silicon dioxide (SiO₂) powder collected as a by-product from silicon metal and ferrosilicon alloy furnaces. This grayish-white powder features an average particle size of 0.1-0.3 microns with very high specific surface area (15-30 m²/g), high pozzolanic activity, and excellent filling properties.