Snow crystals are almost flat and show a particular structure:
* reflecting a small piece in mirrors you can reconstruct the whole crystal - check out which angles between the mirrors work!
* you can superimpose the original crystal with a rotated one - check out which angles of rotation work!
To summarize these properties in mathematical terms, you can says that the symmetry group of a snow crystal is dihedral of order 12.
This video is a draft version of a video that I realised for the MuSe, the new science museum of Trento (muse.it).