International
Tables for
Crystallography
Volume F
Crystallography of biological macromolecules
Edited by E. Arnold, D. M. Himmel and M. G. Rossmann

International Tables for Crystallography (2012). Vol. F, ch. 2.1, p. 52

Table 2.1.3.4 

J. Drentha*

aLaboratory of Biophysical Chemistry, University of Groningen, Nijenborgh 4, 9747 AG Groningen, The Netherlands
Correspondence e-mail: j.drenth@chem.rug.nl

Table 2.1.3.4| top | pdf |
The seven crystal systems

Crystal systemConditions imposed on cell geometryMinimum point-group symmetry
Triclinic None 1
Monoclinic Unique axis b: [\alpha = \gamma = 90^{\circ}] 2
Orthorhombic [\alpha = \beta = \gamma = 90^{\circ}] 222
Tetragonal [a = b\semi\, \alpha = \beta = \gamma = 90^{\circ}] 4
Trigonal Hexagonal axes: [a = b\semi \,\alpha = \beta = 90^{\circ}\semi\,\gamma = 120^{\circ}] 3
  Rhombohedral axes: [a = b = c\semi\,\alpha = \beta = \gamma]  
Hexagonal [a = b\semi\,\alpha = \beta = 90^{\circ}\semi\,\gamma = 120^{\circ}] 6
Cubic [a = b = c\semi\,\alpha = \beta = \gamma = 90^{\circ}] 23
A rhombohedral unit cell can be regarded as a cube extended or compressed along the body diagonal (the threefold axis) (see Fig. 2.1.3.2).