Is Every Snowflake Actually Unique?

As the very first ice crystals come together in a group of fledgling snowflakes, the new flakes often look strikingly similar. That's in large part due to the fact that ice crystals typically take a hexagonal (six-sided) lattice shape because of the way hydrogen atoms bond with oxygen to make water.

Certain edges of the ice crystals are jagged. These ragged, uneven areas attract more water molecules than the smoother and more uniform parts of the hexagon. Each little arm sprouts more of the same, growing into an intricate and uniform snowflake.

If snowflake development stopped within the first few moments of birth, we'd wind up with a lot more flakes that look suspiciously alike. But snowflakes keep gathering more and more crystals, clustering together on top of one another in distinct patterns.

As those clusters of crystals continue their snowflake fiesta, other guests visit the flake-making party. They come in the form of environmental factors, notably humidity and temperature. Both play major roles in whether the snowflake gets bigger and bigger or fizzles out.

You can imagine how critical temperature is to ice crystal formation and structure. Between temperatures of 27 and 32 degrees Fahrenheit (-2.8 and 0 degrees Celsius), crystals take on a plate-like or prism appearance. These are prototypical six-armed snowflakes that lack much visual interest.

Drop the temperature a few degrees and you'll see needle-like structures. Hollow columns develop at even lower temperatures. And when it's crazy cold you'll see stars sprouting fern-like arms.

Lower humidity tends to result in flatter flakes. Higher humidity means more crystal development in edges and on corners. Add some extra moisture at those really frigid temperatures and suddenly snowflakes may become mesmerizingly beautiful. They contain a multitude of intersecting plates and needles and spaces, minute masterpieces falling from the heavens.

Physics and weather conditions determine snowflake shape and size. Math determines that those flakes are unique.

Consider that each snowflake is made up of a huge number of water molecules. By one estimate, a flake may have as many as a quintillion molecules [source: Palmer]. Because each little branch of a snowflake can spawn many others, there are dozens and dozens of ways for various crystalline features to join. There are so many possible arrangements that some scientists say there are twice as many possible crystal combinations as there are atoms in the whole universe [source: Zentile].

Those kinds of numbers are so large that we can't really even comprehend them. But if the math holds, those numbers mean it's awfully unlikely that any two snowflakes have ever been — or will ever be — exactly alike.

Furthermore, there are all kinds of other factors at play in snowflake formation at any given instance. Even the tiniest fluctuation in temperature and humidity alters crystal construction. Minute impurities like flecks of dust change the crystals, too. The angles at which water molecules collide with existing crystals matter as well.

In the swirling atmosphere miles above the Earth's surface, all of these variables ceaselessly change. Conditions that hold in one small space are just a tiny bit different than those inches in any direction, and all of it transforms crystals and their subsequent snowflakes in infinite ways.

Snowflakes smash into each other as they zoom and swoop through the air. Where their branches shatter, new ones form, adding to the uniqueness of every translucent little flake.

So snowflakes really are nearly unlimited in their specialness. They're tiny and ephemeral testaments of the strange and constant change in the world and universe all around us.