Here's why:

* Minerals: Rocks are primarily composed of minerals, which are naturally occurring, solid substances with a defined chemical composition and crystal structure.

* Other Substances: Rocks can also contain other substances, like:

* Organic matter: Fossil remains, plant material, etc.

* Glass: Volcanic glass, for example.

* Water: In some cases, rocks can contain trapped water.

* Air: Pores within the rock can contain air.

Let me know if you'd like to explore different types of rocks!