Some Smarts for You
DID YOU KNOW THAT SNOWFLAKES ARE HEXAGONAL?
A snowflake always has six lines of symmetry, which arises from the hexagonal crystal structure of ordinary ice (known as ice Ih) along its 'basal' plane. There are, broadly, two possible explanations for the symmetry of snowflakes. Firstly, there could be communication or information transfer between the arms, such that growth in each arm affects the growth in each other arm. Surface tension or phonons are among the ways that such communication could occur. The other explanation, which appears to be the prevalent view, is that the arms of a snowflake grow independently in an environment that is believed to be rapidly varying in temperature, humidity and other atmospherical conditions. This environment is believed to be relatively spatially homogeneous on the scale of a single flake, leading to the arms growing to a high level of visual similarity by responding in identical ways to identical conditions, much in the same way that unrelated trees respond to environmental changes by growing near-identical sets of tree rings.
However, the concept that no two snowflakes are alike is not necessarily true. Strictly speaking, it is extremely unlikely for any two objects in the universe to contain an identical molecular structure; but, there are, nonetheless, no known scientific laws which prevent it. In a more pragmatic sense, it's more likely, albeit not much more, that a pair of snowflakes are visually identical if their environments were similar enough, either because they grew very near one another, or simply by chance.
The American Meteorological Society has reported that matching snow crystals were discovered by Nancy Knight of the National Center for Atmospheric Research. The crystals were not flakes in the usual sense but rather hollow hexagonal prisms.