Are snowflakes always hexagonal?

Today was a beautiful sunny fall day. Mika and I went to the park and had ice cream. There was a little snowflake on the ice cream cup, which got me thinking. I have noticed that drawings of snowflakes often have six corners. But is this also the case in nature? And if so, why? I asked Arctic scientist Nina Maherndl. After all, Nina has often told me interesting things about clouds, ice crystals and snowflakes.

When I asked her “Are snowflakes always hexagonal?”, Nina replied: “Yes and no. It depends on what exactly you mean by “snowflake”. At cold temperatures, ice crystals can form in the atmosphere by water freezing. These ice crystals are actually hexagonal. This is thanks to the building blocks that make up water: oxygen and hydrogen.” Nina drew me a little sketch. She drew a sphere in the middle (oxygen) and two smaller spheres below it on the left and right (hydrogen). Chemically speaking, water looks triangular. When many so-called water molecules come together to form ice, they prefer to arrange themselves in hexagonal structures.

“The shape of the ice crystals – for example, whether they look like hexagonal plates or have the classic dendrite shape – depends on the temperature and humidity. Every ice crystal is unique,” Nina continued. Hmmm, that sounds like a pretty clear answer. Why was Nina so hesitant before? Could it perhaps be because snowflakes can consist of several ice crystals?

“That’s right. Ice crystals can stick together and form so-called “aggregates”. Aggregate snowflakes are not necessarily hexagonal. Ice crystals can also break apart. Or water droplets can freeze on snowflakes and form spherical-looking graupel.”

Wow, I’ve learned something exciting again! As soon as it snows in winter, I really want to see the shape of snowflakes for myself. But that probably won’t happen for a while. Until then, I’d better take Mika to the park in the fall and eat ice cream more often.

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