Mineralogists (scientists who study minerals) use the term "mineral" for a substance that has all four of the following features:
1. It must be found in nature.
2. It must be made up of inorganic substances (substances that were never alive).
3. It must have the same chemical makeup regardless of where it is found.
4. Its atoms must be arranged in a regular pattern and form solid crystals.
"Rocks" are generally defined as an aggregates, or combinations, of two or more minerals. However, some geologists (scientists who specialize in the study of the origin, history, and structure of the Earth) extend the definition of rocks to include clay, sand, and certain types of limestone.