Here's why:

* Natural: Minerals are formed by natural processes, not man-made.

* Solid: They have a definite shape and volume.

* Crystals: Minerals are made of repeating units of atoms arranged in a highly ordered, three-dimensional pattern. This pattern is what creates the characteristic crystal shapes you often see.

Examples of minerals:

* Quartz (SiO2)

* Diamond (C)

* Halite (NaCl)

* Feldspar (various chemical compositions)

Let me know if you want to learn more about a specific mineral!