Identical snowflakes

The widespread claim that no two snowflakes are alike is not in practice true. It is however the case that as a result of turbulent air currents a collection of snowflakes that fall to the ground in a particular region will often have come from very different regions of a cloud, and therefore will have grown in different environments. Note that the reason that the six arms of a single snowflake usually look the same is that all of them have grown in essentially the same environment. Deviations are usually the result of collisions between falling snowflakes.