KENNETH LIBBRECHT / SCIENCE PHOTO LIBRARY KENNETH LIBBRECHT / SCIENCE PHOTO LIBRARY
Timelapse microscope view of a growing snowflake. Snowflakes are symmetrical ice crystals that form in moist, freezing cold air. They display hexagonal symmetry as molecules of water form a hexagonal lattice, and the molecular-scale structure dictates the larger scale structure of the ice crystals. Initially the flake forms a hexagonal prism, but as this gets larger spikes appear at its vertices, which branch and form different structures. The growth of a snowflake depends on the conditions within its cloud, and they are extremely sensitive to temperature and humidity. On the scale of the flake these parameters are very similar, giving rise to the symmetry, but each flake follows a very different path through the cloud as it grows, so no two flakes will ever have the exact same structure.
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