All the crystals whose faces can be reffered to two equal horizontal axes and a third vertical axis which is either longer or shorter than the other two. All the three axes are at right angles. The two horizontal axes are inter changeable and are denoted by a1(running from front to back) and a2( running from right to left). The vertical axis is C. The values of angle alpha, beta and gamma is 90 degree.
The symetry class which belong to this system is :
Zircon Type or Ditetragonal-bipyramidal Class
The symmetry of this class can be deduced from the typical form cube.
Planes 5 - 3 Axial (1 horizontal and 2 vertical) and 2 diagonal vertical.
Axes 5 - 4 of two fold, 1 of four fold.
A centre of symmetry.
1)Basal Pinacoid - It is an open form consisting of two faces. Each face cuts onlt the vertical axis and is parallel to the horizontal axis. The Miller symbol is (001).
2)Tetragonal prisam of Second order - It is an open form consisting of 4 vertical faces, each face cuts only one horizontal axis and is parallel to other two axes. It's Miller symbol is (100).
3)Tetragonal prism of First order - It is an open form consisting of 4 vertical faces, each face cuts two horizontal axes at equall distance and is parallel to the vertical axis. It's Miller symbol is (110).
4)Ditetragonal Prism - It is an open form having 8 vertical faces , each face cuts horizontal axes at unequall distance. It's Miller symbol is (210).
5)Tetragonal Bipyramid of Second order - It's a solid having 8 triangular faces, each face cuts vertical axis and one horizontal axis.It's Miller symbol is (101).
6)Tetragonal Bipyramid of First order - It's a solid having 8 isosceles triangular faces. Each face cuts all the three axes. It's Miller symbol is (111).
7)Ditetragonal Bipyramid - It's a solid having 16 scalene faces. Each face cuts all the three axes at different lengths. It's Miller symbol is (211).
Zircon - Combination of
Rutile -
Cassiterite -
Anatase Idocrase, Apophyllite.