What Is the General Structure of a Snowflake?
Most people don't get more than a passing glance at a snowflake, since the flakes melt or quickly bunch together with other snowflakes, losing their identity. Individual snowflakes really do have a unique properties, however, which are built upon a general six-sided structure of frozen water. Scientists are still studying snowflakes and their characteristics to learn more about how this structure is formed.
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Terminology
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The term snowflake is actually slightly inaccurate in most uses. If you mean a single entity of ice, the proper term is snow crystal. "Snowflake" is often used generally to refer to a single snow crystal or a few snow crystals that are stuck together.
Molecular Structure
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Although you can't see it with the naked eye, a snow crystal's molecular structure looks like latticework. Oxygen atoms are bound together with hydrogen atoms in symmetrical hexagons to form the lattice. The chemical formula for a snow crystal is H2O, since snow is made of water.
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Hexagonal Prism
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Snowflakes all start as hexagonal prisms, which look like a tube but with six flat sides instead of being circular. These prisms can be short and wide (plates), tall and thin (columns) or proportional. As they grow, branches develop, forming what we traditionally picture as a snowflake shape.
Branching Morphology
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The final structure of a snow crystal depends on the temperature and the water saturation of the air. The "normal" structure that most people picture when they think of a snowflake shape is called a dendrite, and these form at two points---when the air is moderately saturated and the temperature is right around freezing or when the air is extremely saturated and the temperature is around zero degrees Fahrenheit. Otherwise, the snow crystals form into more oddly shaped columns or plates. The physics behind why and how snow crystals grow with different shapes is still not understood very well.
Uniqueness
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Many people question whether snowflakes actually are unique. It can't be scientifically proved, because you would have to gather every snow crystal in the world to compare them. But it is extremely unlikely that any two snow crystals are exactly alike. Snow crystals that are still hexagonal prisms without branches might look alike, but when the branches start to grow, the snowflake develops hundreds of features. And since even just 15 features can be arranged in more than a trillion different ways, it is unlikely that 100 features or more would ever be arranged in exactly the same way twice.
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References
- Photo Credit branch in snowflake image by air from Fotolia.com
