No two snowflakes are alike, yet every one has exactly six arms, because ice freezes on a hexagonal lattice and all the branches growing from a single seed meet the same conditions. Temperature and supersaturation together set the growth habit: heavy supersaturation throws out ragged dendritic branches, while slow cooling yields fewer crystals that are larger and flat-faced. The underlying lattice changes with the substance: ice packs hexagonally, table salt in a face-centred cubic arrangement, and diamond in a lattice of its own where every carbon atom bonds to four neighbours.
No two snowflakes are alike, yet every one has exactly six arms, because ice freezes on a hexagonal lattice and all the branches growing from a single seed meet the same conditions. Temperature and supersaturation together set the growth habit: heavy supersaturation throws out ragged dendritic branches, while slow cooling yields fewer crystals that are larger and flat-faced. The underlying lattice changes with the substance: ice packs hexagonally, table salt in a face-centred cubic arrangement, and diamond in a lattice of its own where every carbon atom bonds to four neighbours.
Related topics in Matter & Atom