Snowflakes pentagonal

Squares, rectangles, parallelograms, rectangular solids, octahedra, and snowflakes have inversion centers tetrahedra, triangles, and pentagons do not (Figure 4-5). 

The combination of symmetries considered in this section is labeled m-n m, and it is characteristic of highly symmetrical objects. Accordingly, their shapes are relatively simple. As seen in Figure 2-26, some fundamental shapes have m-tv.m symmetries. Examples include the square prism, m-4 m, the pentagonal prism, m-5 m, the trigonal bipyramid, m-3 m, the square bipyramid, m-4-.m, and the bicone, the cylinder, and the ellipsoid, all having symmetry. One of the most beautiful and most common examples of this symmetry is the m-6.m symmetry of snowflakes. 

Pentagonal Snowflake. Computer drawing, courtesy of Robert H. Mackay,... 

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