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When you think of “variety of ice cream” you probably think of the wide range of ice cream parlors.

But even with pure water ice, i.e. frozen H2O, there is a great variety.

So far, physicists were familiar with 18 different forms of crystalline ice.

Now researchers at the University of Innsbruck have discovered another type of ice: Ice XIX.

The different types of ice differ in the arrangement of their atoms in the crystal.

In the ice crystals of the snowflakes, the oxygen atoms are arranged hexagonally.

In physicists' nomenclature, this type of ice cream is referred to as ice cream number 1 (ice cream I).

It is the only type of ice cream that occurs naturally on earth.

All other types of ice cream have to be laboriously manufactured in the laboratory.

There are, however, two small exceptions.

The types of ice cream VI and VII, whose structures can only develop under high pressure, have been found in the form of small inclusions in diamonds.

They evidently arose under the pressures in the earth's mantle.

These two ice exotics have made it onto the official list of minerals, which is edited by the International Mineralogical Society.

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The different types of ice have very different physical properties - for example, significantly different melting points.

The Innsbruck researchers compare this with the great variety of manifestations of the chemical element carbon.

Materials as diverse as graphite, graphene or diamond all consist exclusively of carbon atoms.

The different arrangement of these atoms leads to the enormous differences in the material properties.

The melting points of the different types of ice are sometimes several hundred degrees Celsius apart.

Ten years ago, the Innsbruck researchers succeeded in producing Ice XV for the first time using a special temperature and pressure treatment.

Three years ago they carried out experiments with Ice XV again.

They cooled it down much more slowly than ten years ago and, at the same time, gradually increased the pressure to up to 20,000 bar.

This apparently created another, previously unknown form of ice - Ice XIX.

Ice crystals on a disc.

This is ice cream number 1

Source: Getty Images

"We were immediately sure that it had to be a new variant," reports Thomas Lörting from the Institute for Physical Chemistry at the University of Innsbruck.

But it is not that easy to determine the exact arrangement of the atoms in a crystal structure of ice.

This requires neutron radiation, which can only be made available in a few special research reactors.

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Now the Innsbruck scientists report in the journal "Nature Communications" that they have succeeded in deciphering the crystal structure of Ice XIX in the Rutherford Appleton Laboratory in England.

And yes, it's a new structure that doesn't match any of the other 18.

However, it is very related to the structure of Ice XV.

Both Ice XIX and Ice XV have the oxygen atoms in exactly the same positions.

Only the hydrogen atoms are arranged differently.

In this sense, these two ice forms are the first “twin pair” among the ice structures.

The basic research of the Lörting team is also of interest to astrophysicists.

If not on earth, then under the special pressure and temperature conditions, exotic ice forms beyond Ice I may well occur on other celestial bodies.

For example, layers of different types of ice can be found on the surface of Jupiter's moon Ganymede.