Here's why:

* Quartz is a mineral: Quartz is a naturally occurring mineral composed of silicon and oxygen atoms.

* Chemical composition: The chemical formula for quartz is SiO2, indicating that it consists of one silicon atom bonded to two oxygen atoms.

* Crystal structure: Quartz has a specific crystal structure where the silicon and oxygen atoms are arranged in a three-dimensional lattice. This structure contributes to its hardness and other properties.

While quartz can occur in various colors (due to impurities), the pure form is indeed colorless and hard.