Crystallography : Cubic System Galena type

CUBIC SYSTEM
Type: Galena
CRYSTALLOGRAPHIC AXES:
There 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. All of these three axes are interchangeable due to the above relations.
DIAGRAM:
ELEMENTS OF SYMMETRY:
(1) Planes of symmetry - 9 (3 axial, 6 diagonal)
(2) Axis of symmetry - 13 (3 axis of four fold,, 4axis of three, six axis of two fold)
(3) Centre of symmetry - Present
FORMS:
(1) Cube :- It consists of 6 similar square shaped faces, index face cutting a1 axes and remaining parallel to the other two axes (100)
(2) Octahedron :- It consists of 8 similar equilateral triangular faces, index face cutting all the three axes at equal length (111)
(3) Trias-octahedron :- It consists of 24 isosceles triangular faces, index face cutting two axes at equal length and the third axes at longer length (hh1)
(4) Rhomb-do-decahedron :- It consists of 12 similar rhomb shaped faces, index face cutting two axes at equal length and remaining parallel to the third axes (110)
(5) Hexa-octahedron :- It consists of 48 similar triangular shaped faces, index face cutting all the three axes at unequal distance (hk1)
(6) Tetra-hexahedron :- It consists of 24 similar faces, index face cutting 2 axes at unequal length and remaining parallel to third axes (hk0)
(7) Trapezohedron :- It consists of 24 similar trapezium shaped faces, index face cutting two axes at equal distance and third at a shorter distance (h11)
RULE FOR HOLDING POSITION
The three axis of four fold symmetry should coincide with the three crystallographic axes.
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