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Revision of Crystallographic System
Crystals are solid bodies bounded by smooth surfaces usually flat, arranged on a definite plan, which is an outward expression of the internal arrangement of the atoms, these flat surfaces of a crystal are called as faces. The study of crystals is called as crystallography.
SYMMETRY:
When we look at a crystal we find that there is certain regularity in the position of like faces, edges, etc. This regularity constitutes the symmetry of the crystals. Plane of symmetry is an imaginary plane which divides a crystal into two similar and similarly placed halves. In other words, such plane divides the crystal so that one half is the mirror image of the other.
AXIS OF SYMMERY:
It is an imaginary line along which if a crystal is rotated, a similar face or edge or corner occupies a similar position more than once through a complete rotation of 360°. Depending upon the degree of symmetry, a face may occupy the same position two, three, four, or six times in a complete rotation.
CENTRE OF SYMMETRY:
It is an imaginary central point within a crystal from which similar faces, edges or corners are placed at equal distances on opposite side of the central point.
ORTHORHOMBIC SYSTEM
Type: Baryte
CRYSTALLOGRAPHIC AXES:The crystals of orthorhombic system have three crystallographic axes namely a, b, c which are all mutually perpendicular to each other and are of unequal lengths.The c-axes is vertical and a and b axes are horizontal. The a axes is shorter than b axes and it runs from front to back which is known as brachy axes. The b axes runs from right to left and it is also called macro axes.
ELEMENTS OF SYMMETRY:
(1) Planes of Symmetry - 3 (2 vertical, 1 horizontal)
(2) Axes of symmetry - (32)
(3) Centre of Symmetry – Present
CUBIC SYSTEM
Type: Galena
CRYSTALLOGRAPHIC AXESlThere are three crystallographic axes which are mutually perpendicular to each other and all of these axes are equal in length. These axes are generally denoted as a1, a2 and a3.Axes a1 runs from front to back, axes a2 runs from right to left and axes a3 runs from top to bottom.
ELEMENTS OF SYMMETRY:
(1) Planes of symmetry - 9 (3 axial, 6 diagonal)
(2) Axis of symmetry - 13 (34, 43, 62)
(3) Centre of symmetry - Present
TETRAGONAL SYSTEM
Type: Zircon
CRYSTALLOGRAPHIC AXES: There are three crystallographic axes namely a1, a2 and c which are mutually perpendicular to each other. The axes a1 and a2 are horizontal and equal in length, a1 runs from front to back, a2 runs from right to left. c axis is vertical which may be shorter or longer than the horizontal axes.
ELEMENTS OF SYMMETRY:
(1) Planes of symmetry - 5 Planes (3 axial, 2 diagonal)
(2) Axes of symmetry - 5 (14, 42)
(3) Centre of symmetry - Present
MONOCLINIC SYSTEM
Type: Gypsum

CRYSTALLOGRAPHIC AXES:There are 3 crystallographic axes a, b and c which are unequal in length, a axes is inclined to c axes. The b axes running from right to left is known as ortho axis while a axes runs from front to back in upward direction is called as clino axis. The c- axes is vertical.
ELEMENTS OF SYMMETRY:
(1) Planes of symmetry - 1 (1V)
(2) Axis of symmetry - 12 (along b axis)
(3) Centre of symmetry – Present
TRICLINIC SYSTEM
Type: Axinite
CRYSTALLOGRAPHIC AXES:There are 3 crystallographic axes namely a, b & c which are unequal in length. a axes is inclined to c axes and is called as Brachy axes, b axes is also inclined to c axes and is called as Macro axes. The c axes is called as Vertical axes.
ELEMENTS OF SYMMETRY:
(1) Plane of symmetry: Absent
(2) Axis of symmetry: Absent
(3) Centre of symmetry: Present
HEXAGONAL SYSTEM
Type: Beryl

CRYSTALLOGRAPHIC AXES:Unlike other crystallographic systems, Hexagonal system has four crystallographic axes, the c- axes running from top to bottom. It may be longer or shorter than other 3 axes which are horizontal. The three horizontal axes are equal in length and make an angle of 1200 with one another. These axes are denoted as a1, a2 and a3.
ELEMENTS OF SYMMETRY:
(1) Planes of symmetry – 7 (6V, 1H)
(2) Axis of symmetry – 7 (62, 16)
(3) Centre of symmetry – Present
F.Y.B.Sc (Theory &Practical)

Crystallography Elements of Symmetry    • Crystallography - Elements of Symmetry I  ...  
Orthorhombic System Type Baryte    • Orthorhombic System : Type Baryte  
Tetragonal System Zircon Type    • Crystallography -Tetragonal System  Zircon...  
Hexagonal System Beryl Type )    • Crystallography: Hexagonal System Beryl Type  
Cubic System (Type: Galena)    • Crystallography : Cubic System Galena type  
Monoclinic System (Type: Gypsum    • Crystallography : Monoclinic system - Gyps...  
Triclinic System (Type: Axinite)    • Crystallography : Triclinic System Type Ax...