# Symmetry

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--Doos 06:10, 19 November 2006 (PST) |

## Basic

### Axes of symmetry

Axes of symmetry have to do with balance of shape when rotated around these imaginary axes.

Every crystal belongs to a particular crystal system (cubic, tetragonal, hexagonal, trigonal, orthorhombic, monoclinic or triclinic) and the symmetry for each of these systems is defined by ideal shapes.

Following is an illustration of symmetry axes in the orthorhobic system.

When determining the axes symmetry it is important to rotate (or spin) the crystal around that axis through a 360° rotation and judge how many times the exact image is repeated during the rotation.

As can be seen in the above images there are 3 axes of symmetry in the orthorhombic system and each axis produces the same image twice during a 360° spin around that axis.

When an axis shows the same image twice, we name it a 2-fold axis of symmetry (or better: a "digonal axis of symmetry"). So the orthorhombic system is characterized by 3 2-fold axes of symmetry.

Other crustal systems will have less or more axes of symmetry. A 3-fold axis of symmetry means that the image is repeated 3 times (named a "trigonal axis of symmetry") etc.