Snowflakes Under an Electron Microscope

Water molecules in the solid state, such as in ice and snow, form weak bonds (called hydrogen bonds) with one another. These ordered arrangements result in the symmetrical, hexagonal shape of the snowflake. During crystallization, the water molecules align themselves to maximize attractive forces and minimize repulsive forces. Consequently, water molecules arrange themselves in predetermined spaces and in a specific arrangement. Water molecules simply arrange themselves to fit the spaces and maintain symmetry.

Get some buckyballs, spherical rare earth magnets, you'll find hexagons are a very attractive place for them.

http://emu.arsusda.gov/snowsite/stereo/stereo.html