Twin snowflakes. Snowflakes are ice crystals that form under calm weather conditions when the temperature is near the freezing point of water. Snowflakes have six-fold symmetry, but due to slight differences in the conditions in which they form, no two snowflakes are identical. However, if snowflakes are grown close together (as here), then they can form 'twin snowflakes' that appear identical to the human eye. The two basic patterns, which often combine, are plate crystals (flat) and dendritic crystals (branching tree-like patterns).