Quartz has distinctive crystals.
Quartz is one of the most common minerals in the Earth's crust. Most sand is made from small quartz fragments. Quartz's important properties include its composition and crystal structure.
Composition
Quartz is composed of silicon dioxide (SiO2). Silicon sits just below carbon on the periodic table. Because it has a much larger atomic radius than carbon, silicon does not form double bonds with the oxygen atoms in SiO2. It forms single bonds instead. Consequently, each silicon atom in a quartz crystal is at the center of a tetrahedron of oxygen atoms, and each oxygen atom shares two silicon atoms with its neighbors.
Structure
The crystal structure of quartz is complex. The SiO4 units are linked into helical chains that twist around each other. If it's heated to more than 1500 degrees C, however, the structure will change. The quartz will adopt a new structure; each silicon atom will be at the center of a tetrahedron of silicon atoms, but with an oxygen atom in between each pair of silicons.
Features
Pure quartz is colorless and translucent. Impurities in the quartz, however, can add color to the crystal. Popular varieties are amethyst and rose quartz. When compared with other rocks, quartz is highly resistant to weathering.
Tags: atoms with, center tetrahedron, crystal structure, each silicon, each silicon atom, oxygen atom