Silicon dioxide
Silicon dioxide (SiO2) is the chemical compound of silica, which is a prevalent component of rock, soil and sand. The most common form of silica is quartz, and it can break apart into dust microparticles that become respirable crystalline silica. The respirable crystalline silica are particles less than 10 microns (micrometers), which are small enough to enter the part of the lungs were oxygen and carbon dioxide gases are exchanged.