Silica can be a main component of sand. It can also be in soil, mortar, plaster, and shingles. The cutting, breaking, crushing, drilling, grinding, or abrasive blasting of these materials may produce fine to ultra fine airborne silica dust. Silica occurs in 3 forms: crystalline, microcrystalline (or cryptocrystalline) and amorphous (noncrystalline). "Free" silica is composed of pure silicon ...