In non-tropical countries, the major component of sand is silica, and so the chemical formula for sand is therefore SiO2. In silica, the ratio of the number of silicon atoms to the number of oxygen atoms is 1:2.
In sand, this silica usually exists in the form of quartz. Quartz has a chemical formula of SiO2 and adopts a crystal structure where every silicon atom is attached to four oxygen atoms and every oxygen atom is attached to two silicon atoms. In some countries, sand is also made up of calcium carbonate. The chemical formula for calcium carbonate is CaCO3.