There are many ways to classify minerals but the most widely used method today is by chemical composition and crystal structure.

The system divides minerals into Class, (sub-class), Group (sub-group) and Species (sub-species).

(1) Class: Minerals with the same anion. Generally minerals are divided into fifteen major classes:

(2) Sub-class: Some mineral classes may have differences in the structure of the anion group so these are broken down into sub-classes. The very large Silicate class for example can be divided into six sub-classes:

(3) Group: Within a class or sub-class, minerals with similar chemical composition and the same crystalline structure are placed in the same group. Examples include the Feldspar group in the Tectosilicates sub-class or the Pyroxene group and Amphibole group in the Inosilicates sub-class.

(4) Sub-group: If there are two many minerals in a particular group, the cation type and crystal system of the minerals used to define sub-groups. The Feldspar group for example is divided into the two sub-groups of Plagioclase and Alkali feldspar.

(5) Species: Within a family or sub-family, minerals with the same chemical composition and crystalline structure are defined as belonging to the same mineral species, an example being Albite.

(6) Sub-species: Within a mineral species, if physical properties or differences in the amount of trace elements lead to significant differences then sub-species can be defined. Amethyst, Smoky Quartz, Citrine and Rose Quartz are all sub-species of Quartz for example. Sub-species of Beryl include Emerald, Aquamarine, Pezzottaite, Heliodor, Red Beryl and Goshenite.