Ice

Ice is water, frozen into a solid state. Depending on the presence of impurities such as particles of soil or bubbles of gas, it can appear transparent or a more or less opaque bluish-white color.

In the Sol System, ice is abundant and occurs naturally from as close to Sol as Mercury to as far as the Oort cloud. Beyond the Solar System, it occurs as interstellar ice, on planets and celestial bodies. It is abundant on Terra's surface – particularly in the polar regions and above the snow line – and, as a common form of precipitation and deposition, plays a key role in Terra's water cycle and climate.

Ice molecules can exhibit up to sixteen different phases (packing geometries) that depend on temperature and pressure. When water is cooled rapidly (quenching), up to three different types of amorphous ice can form depending on the history of its pressure and temperature. When cooled slowly correlated proton tunneling occurs below 20 K giving rise to macroscopic quantum phenomena. Virtually all the ice on Terra's surface and in its atmosphere is of a hexagonal crystalline structure denoted as ice Ih (spoken as "ice one h") with minute traces of cubic ice denoted as ice Ic. The most common phase transition to ice h occurs when liquid water is cooled below 0°C (273.15K, 32°F) at standard atmospheric pressure. It may also be deposited directly by water vapor, as happens in the formation of frost. The transition from ice to water is melting and from ice directly to water vapor is sublimation.

Ice is used Unionwide in a variety of ways, including cooling, winter sports, ice sculpture and the water trade.