Snow, as seen through an electron microscope
Why does water forms such shapes when it freezes you ask?
Our understanding, at least…
Ice, which is the form water droplets take when freezing around small dust particles in the atmosphere, is hexagonal. The whole structure stems from this.
On the small scale, it’s easier for the water molecules to stay in place on a rough surface than a smooth one, so “missing” parts in the edge of the crystal get filled in, before eventually a molecule is forced to start a new row because there are no more gaps, which is why they grow larger, flat sided crystals – on the small scale, you can get perfectly hexagonal flat crystals as snowflakes.
At some point, as they grow and move around, instabilities mean it is more favorable to grow from the tips rather than fill in the faces – this depends on the exact environmental conditions, but as snowflakes are so small but moving up and down in the atmosphere, the same conditions can suddenly apply at all six corners at once.
So the end result is complex, often symmetrical structures.