Snowflakes morphology

One of the most beautiful and most common examples of this symmetry is the m-6 m symmetry of snow crystals. The virtually endless variety of their shapes and their natural beauty make them outstanding examples of symmetry. The fascination in the shape and symmetry of snowflakes goes far beyond the scientific interest in their formation, variety, and properties. The morphology of the snowflakes is determined by their internal structures and the external conditions of their formation. The mechanism of snowflake formation has been the subject of considerable research efforts. It is well known that... 

The crystal is a fractal structure and the organization of the primitive unit cells can often be seen in the shape of the macroscopic crystal. A classic example of the fractal repetition of the unit cell is the crystalline structure of a snowflake. The unit cells have the ability to build into a variety of complex shapes, yet each unit cell retains its perfect structure. The primary unit cell structure in the case of a snowflake is hexagonal and undergoes dendritic growth to produce an array of different macro crystals (Figure 2.4). The final shape of the snow crystal will depend on the conditions used in the growth process (temperature, humidity, etc), which leads to a wide variety of observed morphologies. 

The plot in Fig. 2.11 shows the actual crystal size measurements for a variety of temperatures. The plots show a constant growth rate for every temperature. The actual data are listed in the bottom table of Fig. 2.11. The linear increase in crystal size observed in the present example is lost as soon as transport processes become rate-determining. Transport control is observed when crystal growth is so fast that for solution crystallization, as an example, the solvent can not diffuse away from the crystal surface fast enough to maintain constant concentration. In the case of melts, the heat of crystallization may build up on fast crystallization and raise the temperature, and thus slow down crystallization temporarily. One can spot transport control by the dendritic, snowflake-like crystal morphology it produces. 

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