Symmetries in a snow crystal - MathLapse
Snow crystals have many beautiful symmetries.
We can reproduce a snow crystal from a smaller part using a pair of mirrors with angles 180° (that is, a single flat mirror), 120°, 90°, 60° or 30°. No other angle works.
We can also rotate the crystals by multiples of 60° and get a perfect copy which can be superimposed to the original crystal.