I
water and water vapour.
Below 32 kF (0 kC), liquid water forms a hard solid and water vapour forms frost on surfaces and snowflakes (see snow ) in clouds. Unlike most liquids, water expands on freezing, so ice is less dense than liquid water and therefore floats. It consists of compact aggregates of many crystal s (with hexagonal symmetry), although ice formed from the bulk liquid does not normally have crystal faces. Molecules in the crystal are held together by hydrogen bonds (see hydrogen bonding ). With a very high dielectric constant, ice conducts electricity much better than most nonmetallic crystals. At very high pressures, at least five other crystal forms of ice occur.
II
[c mediumvioletred] (as used in expressions)
dry ice
Greenland Ice Sheet
ice age
ice cream
ice dancing
ice formation
ice hockey
Larsen Ice Shelf
Laurentide Ice Sheet
Ross Ice Shelf
sea ice