Although ice might seem simple, it is complicated stuff

Sunday, April 11th, 2021

Regular six-sided crystals of ice are actually just one of ice’s many forms, or polymorphs, the form known as ice 1. Now ice 19 has been discovered:

Although ice might seem simple, it is complicated stuff. For instance, only the oxygen atoms in the water molecules of six-sided ice crystals form a hexagonal shape, while their hydrogen atoms are randomly oriented around them. This makes ice I a “disordered” or “frustrated” ice in the terminology of ices. One of the properties of such disordered ices is that they can deform under pressure: “This is the reason why glaciers flow,” Loerting said.

In contrast, the hydrogen atoms in several of the other polymorphs of ice also have their own crystal patterns, and they are called “hydrogen-ordered” or “H-ordered” as a result. Unlike disordered ices, H-ordered ices are very brittle and will shatter, rather than deform, he said.

In those terms, the newly identified 19th form of ice is an H-ordered ice; in fact, it’s an H-ordered form of a disordered ice, called ice VI, which has a random pattern of hydrogen atoms. And ice VI also has yet another H-ordered polymorph, ice XV, in which the hydrogen atoms are aligned in an entirely different pattern.

“Ice VI, ice XV and ice XIX are all very similar in terms of density [because] they share the same kind of network of oxygen atoms,” Loerting said. “But they differ in terms of the positions of hydrogen atoms.” It’s the first time that such a relationship between ice polymorphs has been discovered, and it could allow experiments to study transitions between one form and another, he said.

Naturally this reminded me of ice-nine, from Kurt Vonnegut’s Cat’s Cradle:

Ice-nine is an alternative structure of water that is solid at room temperature and acts as a seed crystal upon contact with ordinary liquid water, causing that liquid water to instantly transform into more ice-nine.


  1. Grasspunk says:

    You wonder if they’d deliberately skip Ice IX.

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