Morphology snow crystals

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... 

Figure 2.4 Examples of several different morphological types of snow crystals found in nature. Reproduced from reference 5.

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. 

Kobayashi, T. and Kuroda, T. (1987) Snow crystals, in Morphology of Crystals-Part B, Terra Scientific Publishing Company, Tokyo. 

The snow and frost described are almost assuredly of different morphology, particle size, and size distribution than the starting material Hannay and Hogarth studied salts such as cobalt chloride and potassium iodide. Incidentally, the reference to the precipitation of the solid is not an Isolated report of nucleation from a supercritical fluid. For example, many other references to snow, fog, fumes, and crystals formed during depressurization of a solution of a solute in a supercritical fluid have been made by researchers studying supercritical fluid solubility phenomena. 

Cabanes, A., Legagneux, L., Domine, R 2002. Evolution of specific surface area and of crystal morphology of arctic fresh snow during the ALERT 2000 campaign. Atmospheric Environment 36, 2767-2777. 

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