A 6-fold symmetric ice crystal grows branch-by-branch from its center, then gently rotates before resetting and regrowing. Real snow crystals form this way because water molecules bond into a hexagonal lattice, forcing 6-fold symmetry as ice accretes fastest at the six corners where curvature (and vapor exposure) is greatest -- a process called the Mullins-Sekerka instability. Wilson Bentley photographed over 5000 snowflakes from 1885 onward and never found two alike, since a crystal's exact branching pattern depends on the fluctuating temperature and humidity it experiences as it falls. Dendritic (fern-like) branching typically forms near -15 degrees C, while flat plates form near 0 to -3 degrees C. Drag to orbit, scroll to zoom.