Minerals are the building blocks of rocks. If free of any space restrictions when forming, each mineral would exhibit its characteristic crystalline structure. Constrained by the rock, the crystals are smaller, but each discrete mineral is still visible. Rocks may contain a single mineral (such as rock salt, NaCl) or more than one, such as this granite rock that contains three minerals.

THE ROCK CYCLE CONSTANTLY FORMS AND RE-FORMS ROCKS IN EARTH’S CRUST

Rocks form and are transformed when they are subjected to high heat and pressure underground and when they are exposed to wind and water on Earth’s surface.