# Crystal system

### From Online Dictionary of Crystallography

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== Crystal systems in two and three dimensions == | == Crystal systems in two and three dimensions == | ||

In the two-dimensional space there exist four crystal systems: | In the two-dimensional space there exist four crystal systems: | ||

- | * | + | * oblique |

- | * | + | * rectangular |

- | * | + | * square |

* hexagonal | * hexagonal | ||

## Revision as of 07:59, 21 August 2007

Système cristallin (*Fr*); Sistema cristallino (*It*); 晶系 (*Ja*)

## Definition

A crystal-class system, or **crystal system** for short, contains complete geometric crystal classes of space groups. All those geometric crystal classes belong to the the same crystal system which intersect exactly the same set of Bravais flocks.

## Crystal systems in two and three dimensions

In the two-dimensional space there exist four crystal systems:

- oblique
- rectangular
- square
- hexagonal

In the three-dimensional space there exist seven crystal systems:

- triclinic
- monoclinic
- orthorhombic
- tetragonal
- trigonal
- hexagonal
- cubic

Note that the adjective *rhombohedral* refers to a lattice system, not to a crystal system. Rhombohedral crystals belong to the trigonal crystal system, but trigonal crystals may belong to the rhombohedral or to the hexagonal lattice system.

## See also

Section 8.2.8 in of *International Tables of Crystallography, Volume A*