Snowflakes Are Not as Unique as We Thought

December 3, 2015 | Joanne Kennell

A closeup of an intricate snowflake
Photo credit: Alexey Kljatov/Flickr (CC BY-NC 2.0)

Snowflakes can only form 35 different shapes.

Winter is almost here.  Although most of us cringe at the thought of snow and the cold, winter offers some pretty beautiful sights, and one of them is snowflakes.

Now we have been told that all snowflakes are unique — which is true on the molecular level — however, it turns out all snowflakes fall into one of 35 different shapes, according to researchers.  The precise reasons for the formation of various snowflake shapes is not completely understood by scientists, but they have been able to generate a list of eight predominant shapes, with each containing several variations of snowflake structures.  Shapes include: column, plane, combination of column and plane, aggregation, rimed, germs, irregular, and other.

It is important to first understand how a snowflake begins to form before we can appreciate how they take shape.

SEE ALSO: The Science Behind Antifreeze

A snowflake is born when an extremely cold water droplet freezes onto a pollen or dust particle in the air, which creates an ice crystal.  This ice crystal reflects the internal order of the water molecules as they arrange themselves during the process of crystallization, resulting in the formation a hexagonal prism (six faces), with both a top and a bottom.  

Water molecules in the solid state of ice and snow form weak hydrogen bonds to one another, so the water molecules align themselves to maximize the attractive forces and minimize the repulsive ones.  These ordered arrangements result in the symmetrical, hexagonal shape of the snowflake, and as the ice crystal falls towards the ground, water vapor continues to freeze onto the original crystal which builds even more crystals.  The different shapes and patterns of snowflakes occur because of atmospheric conditions of temperature and humidity.

Most important is temperature.  The temperature that each crystal forms determines its basic shape.  For example, simple crystal plate and column structures occur in very cold temperatures, whereas in warmer temperatures snowflakes form beautiful branching patterns.  

Humidity of the air is also important, just not as important as temperature.  Humidity has an effect on the complexity of snowflakes.  More intricate snowflakes form in areas with a lot of moisture in the air, while more simple snowflakes are produced in drier conditions.

These atmospheric conditions are what causes a snowflake’s intricate pattern to form.  A snowflake may be growing one way, and just moments later, if the temperature or humidity changes, it will change its course.  Although the inherent hexagonal symmetry is preserved, the ice crystal may create branches in new directions.  

Since changes in temperature and humidity occur over a large area compared with the size of the snowflake, all parts of the snowflake are similarly affected, adding to its symmetry.

Snowflakes, really they are breathtaking.

Watch this timelapse video of water freezing into intricate snowflakes:


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