Optical microscope photographs of snow crystals.1 Their characteristic 6-fold symmetry is related to the molecular structure of water, which stabilizes in hexagonal lattices at earth temperature and pressure.2 Each crystal has about 1018 molecules of water, and its very specific shape is due to a complex dependence on temperature and humidity change, and to nonlinear diffusion leading to structural branching instabilities and dendritic patterns. Each snowflake registers an history of interactions with the environment, like “a hyeroglyph sent from the sky”.3
- © Kenneth G. Libbrecht (Caltech) [↩]
- Water has several other possible solid phases, depending on pressure and temperature, with different crystal symmetry. Eg. ice-Ic forming at earth pressure and temperature lower than -80°C has cubic symmetry. [↩]
- U. Nakaya, “Snow Crystals: Natural and Artificial”, Harvard University Press (1954) [↩]
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