Why are snowflakes and surface frost flakes symmetrical?
It is hard to imaging how ice can commensurate itself almost exactly, as you can see from these frost photos submitted by Valerie Fogarty of West Penn Township.
Snowflakes and ground frost are symmetrical through the process of crystallization. Ice (primarily wet ice) reflects the internal structure of the water molecules as they arrange themselves to a solid state. Water molecules in this state, such as in ice, surface frost and snow, form fragile  bonds (IE hydrogen bonds) that attach to one another. These arrangements result in the basic symmetrical, hexagonal shape.

SNOWFLAKES:
Snowflake formation is a extremely dynamic process. A snowflake may encounter many different environmental conditions during its growth, while always changing its structure.
In reality, there are many different types of snowflakes. This occurs because each snowflake is itself – a separate crystal that is subject to the specific atmospheric conditions under which it is formed.

The shape of the snowflake an depend on the high of the cloud it was formed in. Six-sided hexagonal crystals are primarily shaped in high clouds. Needles or flat six-sided crystals are shaped in middle height clouds. The wide remaining variety of six-sided shapes are formed in low clouds. Colder temperatures usually produce snowflakes with sharper tips on the sides of the crystals. This leads to branching of the snowflake arms (called dendrites).

Snowflakes that grow under warmer conditions grow more slowly, resulting in smoother, less intricate shapes.

> 32-25° F – Thin hexagonal plates.
> 25-21° F – Needles.
> 21-14° F – Hollow columns.
> 14-10° F – Sector plates (hexagons with indentations).
> 10-3° F – Dendrites (lacy hexagonal shapes).

An average snowflake is made up of about 180 billion molecules of water. Although the snow-water ratio depends on various factors such as temperature, crystal structure and wind speed.
The Guinness Book of World Records states that a giant snowflake was found at Fort Keogh, Montana (on January 28, 1887) with a length of 15 inches and thickness of about 8 inches.

Here is a useful link that helps to explain the process of snow crystallization: http://www.its.caltech.edu/~atomic/snowcrystals/faqs/faqs.htm

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