Quartz crystal structure. Molecular model (ball- and-stick) of the crystalline structure of quartz (silicon dioxide). Atoms (balls) are colour-coded: silicon (red) and oxygen (yellow). Quartz is the crystalline form of silicon dioxide, a mineral that can also form other structures. Crystalline structures are regular, consisting of a unit cell that is repeated millions of times. Quartz has a unit cell consisting of three silicon atoms and of six oxygen atoms. In the overall structure, each silicon atom forms bonds (sticks) with four oxygen atoms, and each oxygen atom forms bonds with two silicon atoms. Quartz is a common mineral in the Earth's crust, found in glass and sand.