Final answer:
The mineral composed entirely of silicon and oxygen is quartz, scientifically known as silicon dioxide or SiO2. It is a significant component of the Earth's crust and comes in various crystalline forms.
Step-by-step explanation:
The common mineral composed entirely of silicon and oxygen is quartz. Quartz is a crystalline form of silicon dioxide (SiO2), which is found in various rock types and is the stable polymorph at the Earth's surface. Silicon dioxide exists in nature in several crystalline forms, with quartz being the most abundant and well-known. The very structure of quartz and other silicates is based on the silica tetrahedron - a geometrical shape with a silicon atom at its center, surrounded by four oxygen atoms. This SiO4 unit can join together in different ways, creating a vast variety of silicate minerals which constitute a large part of the Earth's crust, common rocks, and materials such as ceramics and glasses.