When water is cooled below its normal freezing point, it normally freezes to form hexagonal ice, or Ice I. If it is very pure and cooled carefully, it may be supercooled to about -42°C. If water is cooled very rapidly then it forms an amorphoric glass.
Hyperquenched glassy water (HGW) is formed by the rapid spraying of a fine jet of micrometre-sized water droplets into very cold liquefied gas, usually propane, at around or under 80 K, involving cooling rates greater than 105 K per second.
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