Here's why:

* Mineral Definition: A mineral is a naturally occurring, solid, inorganic substance with a defined chemical composition and a specific crystalline structure.

* Quartz Characteristics: Quartz fits this definition. It's found naturally in the Earth's crust, is solid, inorganic, has the chemical formula SiO₂ (silicon dioxide), and has a specific crystalline structure (usually hexagonal).

Therefore, quartz is a prime example of a mineral.