On this Wikipedia the language links are ice cream cupcakes the top of the page across from the article title. This article is about water ice. For the broader concept of “ices” as used in the planetary sciences, see Volatiles.
The properties of ice vary substantially with temperature, purity and other factors. In the Solar System, ice is abundant and occurs naturally from as close to the Sun as Mercury to as far away as the Oort cloud objects. Beyond the Solar System, it occurs as interstellar ice. It may also be deposited directly by water vapor, as happens in the formation of frost. Ice is used in a variety of ways, including for cooling, for winter sports, and ice sculpting.
As a naturally occurring crystalline inorganic solid with an ordered structure, ice is considered to be a mineral. An unusual property of water is that its solid form—ice frozen at atmospheric pressure—is approximately 8. The density of ice is 0. The effect of expansion during freezing can be dramatic, and ice expansion is a basic cause of freeze-thaw weathering of rock in nature and damage to building foundations and roadways from frost heaving. It has been argued that without this property, natural bodies of water would freeze, in some cases permanently, from the bottom up, resulting in a loss of bottom-dependent animal and plant life in fresh and sea water. Compared with water, this absorption is shifted toward slightly lower energies.
Thus, ice appears blue, with a slightly greener tint than liquid water. Since absorption is cumulative, the color effect intensifies with increasing thickness or if internal reflections cause the light to take a longer path through the ice. Other colors can appear in the presence of light absorbing impurities, where the impurity is dictating the color rather than the ice itself. Because ice in natural environments is usually close to its melting temperature, its hardness shows pronounced temperature variations. Ice may be any one of the 19 known solid crystalline phases of water, or in an amorphous solid state at various densities. Most liquids under increased pressure freeze at higher temperatures because the pressure helps to hold the molecules together.
C, as shown in the phase diagram below. The melting of ice under high pressures is thought to contribute to the movement of glaciers. Ice, water, and water vapour can coexist at the triple point, which is exactly 273. Subjected to higher pressures and varying temperatures, ice can form in 19 separate known crystalline phases. Water in the interstellar medium is dominated by amorphous ice, making it likely the most common form of water in the universe. Ice from a theorized superionic water may possess two crystalline structures.