Silica (silicon dioxide, SiO2) occurs as the mineral quartz, a major constituent in many igneous and sedimentary rocks, and the most common detrital mineral in sandstone.
As a commodity, the term silica is applied to quartz in all its forms — as vein or reef quartz, quartz pebbles, sandstone, quartzite, or as unconsolidated sand. World consumption approximates 120 Mt/year. Quartzite, sand and gravel used for construction purposes are excluded from this category.
The main use of silica is for flat and container glass manufacture, with ~60% of each glass batch being silica sand. Silica sand is bonded with synthetic resins to make moulds and cores for casting metals in metal foundries. In oil drilling, well-rounded sand is used to prop open fissures in reservoir rocks to improve permeability. In the metallurgical industries, lump silica (quartzite) is used as a flux in metal smelting, and as a raw material for the manufacture of ferrosilicon. Silica is used in a variety of ceramics and specialty glasses, and is the raw material for manufacture of silicon compounds such as silicones, silanes, and high-purity silicon metal for semiconductors.
