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Symmetry Elements
Crystals as well as minerals possess definite internal arrangement of atoms which are ordered in a definite three dimensional network called as lattices. When crystals formed at undisturbed environment, the crystal possess smooth planar surface with fine edges. Such crystal faces reflect the internal arrangement of atoms in the crystal or mineral. Symmetry is the identification of two or more things with respect to rotation, reflection or scaling.
In crystallography, symmetry is used to characterize crystals, identify repeating parts of molecules, and simplify both data collection and nearly all calculations. Symmetry elements are of three types
Rotational Symmetry
Reflectional Symmetry
Inversion Symmetry
Rotational Symmetry
Rotational Symmetry or the Axis of Symmetry is an imaginary line, passing through the crystal such that when the crystal is rotated about this line, it presents the same appearance more than once in one complete revolution i.e., in a rotation through 360°.
The axes of Symmetry are determined by number of folds through 360°. They are
1-fold (repeat itself through 360°)
2-fold (repeat itself through 180°)
3-fold (repeat itself through 120°)
4-fold (repeat itself through 90°)
6-fold (repeat itself through 60°).
Reflectional Symmetry
Reflection Symmetry or Plane of Symmetry is defined an imaginary plane which passes through the center of a crystal can divides it into two equal portions which are exactly the mirror images of each other.
Center of Symmetry
Center of symmetry is a point which is located at equal distance from all the faces or points.
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