The chemical combination of silicon and oxygen is called silica. Its chemical formula is SiO₂, meaning each unit contains one silicon atom bonded with two oxygen atoms.
Silica is one of Earth’s most abundant natural materials. It commonly occurs as quartz and is a major ingredient of sand, sandstone, granite, and many other rocks. It also appears in less familiar forms such as opal, diatomaceous earth, aerogel, and silica gel.
A common mix-up is confusing silica with silicone. Silica is an inorganic compound made of silicon and oxygen; silicone is a family of synthetic polymers containing silicon, oxygen, carbon, and hydrogen. Silica is also the main ingredient in most glass and is widely used in ceramics, optical fiber, construction materials, and semiconductor manufacturing.