Orthorhombic crystal system
The orthorhombic crystal system is one of the seven crystal systems in crystallography . It includes all point groups with three mutually perpendicular twofold rotational or rotational inversion axes. The orthorhombic crystal system is also called the rhombic crystal system. The term rhombic should not be confused with rhombohedral.
Point groups
The orthorhombic crystal system includes the point groups and . They form the orthorhombic crystal family and can be described with the orthorhombic grid system .
Grid system
The orthorhombic grid system has holoedry .
In the orthorhombic grid system, the grid axes lie in the direction of the 3 mutually perpendicular axes of symmetry. There are no further conditions for the length of the grid axes. This results in:
To determine which axis is a, b or c, there is only the condition that a righthanded coordinate system should be created. As a rule, the axes are chosen so that the Hermann Mauguin symbol corresponds to the standard of the International Tables for Crystallography . With the HermannMauguin symbols, however, the room groups can be described with regard to any possible choice of axes. Since this happens more often, there is a tabular overview in the International Tables of all the options for describing a room group with any axis selection. It is therefore generally advisable to use the room group number when specifying the room group, as this makes it easier to find.
Bravais grid
There are four Bravais grids in the orthorhombic crystal system . In the standard setup, the bcentered grid does not appear and the acentered grid only occurs in the point group . This is due to the fact that in this point group the grid system is set up in such a way that the twofold axis lies in the direction of the cgrid axis. Therefore it is not possible in all cases to place the grid axes in such a way that only the ccentered grid is used. The orthorhombic grid system is abbreviated with o.
Point groups in the orthorhombic crystal system and their physical properties
To describe the orthorhombic crystal classes in HermannMauguin symbology , the symmetry operations are given with respect to three given directions (viewing directions) in the grid system. As in the monoclinic, the 3 viewing directions correspond to the a (<100>), b (<010>) and c grid axis (<001>). Since all three grid directions are directions of symmetry here, the HermannMauguin short symbol also consists of three details.
It is characteristic of the orthorhombic space groups that there are no 3, 4 or 6 in the HermannMauguin short symbol.
Point group (crystal class)  Physical Properties  Examples  

No.  Crystal system  Surname  Schoenflies icon  International symbol ( HermannMauguin ) 
Tepid class  Associated room groups ( no.) 
Enantiomorphism  Optical activity  Pyroelectricity  Piezoelectricity ; SHG effect  
Full  Short  
6th  orthorhombic  orthorhombicdisphenoidal  D _{2} ( V )  222  222  mmm  1624  +  +    + 
Austinite epsomite 
7th  orthorhombicpyramidal  C _{2 v}  mm 2  mm 2  2546    +  + [001]  + 
Hemimorphite struvite 

8th  orthorhombicdipyramidal  D _{2 h} ( V _{h} )  2 / m 2 / m 2 / m  mmm  4774         
Topaz anhydrite 


For further orthorhombic crystallizing chemical substances see category: Orthorhombic crystal system .
literature
 Hahn, Theo (Ed.): International Tables for Crystallography Vol. A D. Reidel publishing Company, Dordrecht 1983, ISBN 9027714452
 D. Schwarzenbach Kristallographie Springer Verlag, Berlin 2001, ISBN 3540671145
 Will Kleber , HansJoachim Bautsch , Joachim Bohm , Detlef Klimm: Introduction to crystallography . 19th edition. Oldenbourg Wissenschaftsverlag, 2010, ISBN 9783486590753 .
 Walter BorchardOtt Crystallography 7th edition Springer Verlag, Berlin 2009, ISBN 9783540782704