If a substance contracts when it freezes?

The vast majority of substances contract upon freezing. The notable exception is water for which the expansion upon freezing has an enormous impact on the nature of the Earth.

Most substances contract and become denser upon freezing, but water expands and becomes less dense below about 4 ºC. It is this expansion that causes pipes and bottles to crack when their contents freeze, and rocks to split open when water freezes in their crevices. Icebergs and blocks of ice float in water because they are less dense than the water from which they were frozen.

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