Here's why:

* Minerals are naturally occurring, solid substances with a specific chemical composition and a defined crystal structure. Quartz fits this definition, being made of silicon dioxide (SiO2) and having a specific crystalline structure.

* Rocks are made up of one or more minerals. While quartz can be found in many rocks, it is not a rock itself.

Think of it this way:

* A brick is made of clay. Clay is a mineral, while a brick is a rock-like material.

* Quartz is like clay – a building block for rocks.