If the various elements of symmetry are distributed theoretically around a single point in space (i.e. passing through this point, it is found that 32 different arrangements are possible. These different arrangements of the elements of symmetry about a single point are called crystal classes or crystallographic groups or point groups. Further many point groups have the same axial ratios and angles, e.g., five point groups out of 32 have and a: b :c =1: 1 :1, i.e., a = b = c and all these five correspond to the cubic shape. Into his way , the 32point groups have been grouped into seven types on the basis of axial ration and angles. Since the external geometry of a crystal depends upon the axial rations and angles, it implies that seven types which are called crystallographic systems.

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