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Snowflake. Light micrograph of a fernlike stellar dendrite snowflake. Snowflakes are symmetrical ice crystals that form inside clouds when water vapour condenses directly into ice. 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. Dendritic snowflakes are fairly large crystals, typically 2-4 millimetres in diameter, that are easily seen with the naked eye. (KEYSTONE/SCIENCE PHOTO LIBRARY/KENNETH LIBBRECHT/SCIENCE PHOTO LIBRARY)