Water in the solid state; specif. the dense substance formed in nature by the freezing of liquid water, by the condensation of water vapor directly into ice crystals, or by the recrystallization or compaction of fallen snow. It is colorless to pale blue or greenish blue, usually white from included gas bubbles. At standard atmospheric pressure, it is formed at and has a melting point of 0 degrees C; in freezing it expands about one eleventh in volume. Ice commonly occurs in hexagonal crystals, and in large masses is classed as a rock.