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Hollow column snowflake, light micrograph. Snowflakes are ice crystals that form in air that has a temperature near the freezing point of water. If the air is calm, then a symmetrical, hexagonal snowflake can form. The exact shape of each snowflake depends on local climatic conditions within the precise area of the cloud where it is formed. As such, no two snowflakes are identical, with each individual pattern emerging as the crystal grows. Hollow columns are hexagonal column-shaped crystals that form with conical hollow regions in their ends, as seen here. (KEYSTONE/SCIENCE PHOTO LIBRARY/KENNETH LIBBRECHT/SCIENCE PHOTO LIBRARY)