The repeating pattern of a mineral's particles form a solid called a crystal. The particles of a crystal line up in a pattern that repeats. A crystal has flat sides and sharp edges and corners.
Crystal formation is one of the criteria that a substance must have for the substance to be classified as a mineral. The other four criteria are listed below:
- Naturally occurring- Minerals must form from processes within nature (as opposed to biological processes).
- Inorganic- Minerals cannot form from materials that were once living.
- Solid- The particles of minerals cannot flow freely.
- Definite chemical composition- This means that a mineral always has certain elements in a specific proportion.
Additionally, almost all minerals are compounds. Compounds are made of two or more elements that combine in a distinct proportion.