[3][4] The classification of minerals was based on chemical composition by Dana in the fourth edition (1854, in two volumes) of his book System of Mineralogy.
[5][6] For the 20th century, this classification was completed thanks to scientific progress, particularly in the field of crystallography.
Each mineral has a classification number, made up of four numbers separated by dots, enabling unambiguous identification even when minerals are known by several names (synonymy).
The second number represents the mineral type, in some cases taking into account its atomic structure.
The third number represents a group of minerals of similar structure.