While it's common to find quartz in many rocks, it's not a rock type itself. It's a crystalline silica with a specific chemical composition (SiO2).

Here's the difference:

* Rock: A solid, naturally occurring aggregate of one or more minerals. Examples include granite, sandstone, limestone.

* Mineral: A naturally occurring solid with a specific chemical composition and crystal structure. Examples include quartz, feldspar, calcite.

So, quartz can be a component of various rocks, but it's not a rock in itself.