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Ice Ih (pronounced: ice one h, also known as ice-phase-one) is the hexagonal crystal form of ordinary ice, or frozen water. Virtually all ice in the biosphere is ice Ih, with the exception only of a small amount of ice Ic that is occasionally present in the upper atmosphere. Ice Ih exhibits many peculiar properties that are relevant to the existence of life and regulation of global climate.〔For a description of these properties, see ''Ice'', which deals primarily with Ice Ih.〕 Ice Ih is stable down to and can exist at pressures up to 0.2 GPa. The crystal structure is characterized by hexagonal symmetry and near tetrahedral bonding angles. ==Physical properties== Ice Ih has a density of 0.917 g/cm³, less than that of liquid water, due to the extremely low density of its crystal lattice. The density of ice Ih increases with decreasing temperature (density of ice at −180 °C is 0.9340 g/cm³). The latent heat of melting is 5987 J/mol, and its latent heat of sublimation is 50,911 J/mol. The high latent heat of sublimation is principally indicative of the strength of the hydrogen bonds in the crystal lattice. The latent heat of melting is much smaller, partly because liquid water near 0 °C also contains a significant number of hydrogen bonds. The refractive index of ice Ih is 1.31. 抄文引用元・出典: フリー百科事典『 ウィキペディア（Wikipedia）』 ■ウィキペディアで「Ice Ih」の詳細全文を読む スポンサード リンク
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