While the possibility of water in some diamonds has been accepted for quite some time, scientists have now discovered a new form of ice that has never been found on Earth – ice-VII.
The findings were published on Thursday in Science, and represent the first time scientists have found ice-VII on Earth. What’s especially surprising, however, is that the discovery of this new form of ice was actually an accident.
Accidental discoveries are by no means a super rare occurrence in science, and it drives home how much there is left to discover about the world around us. The research team behind the discovery didn’t set out to find a new form of ice, but it turns out that at least a few diamonds harbor ice-VII – ice that is around one and a half times as dense as the ice we’re used to, and boasting a different crystalline structure in atoms as well.
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Normal ice is referred to as ice-I, and the oxygen atoms within organize themselves in a hexagonal shape. In this new form of ice, ice-VII, the atoms instead organize themselves in a cubic shape.
There are actually multiple forms of water ice that form under different pressures and temperature conditions, and this new form of ice is far from the only different setup we’ve discovered thus far. It does represent, however, the first and only time we’ve seen such an arrangement in ice on Earth.
When a solid form of matter is subjected to more and more pressure, the space between the chemical bonds generally starts to decrease and the bonds tilt towards each other. This new form of ice, and ice as a whole, is unique in that when pressure increases, the bonds organize themselves in different arrangements rather than squishing together – explains Oliver Tschauner, a professor of geoscience at the University of Nevada, Las Vegas, and a lead author of the study.
Ice-VII represents a new form of ice that forms upon the highest amounts of pressure. Ice-I is the form of ice we’re all familiar with, but as pressure increases, it will turn into ice-II which has a “rhombohedral structure.” Continue to increase this pressure and you’ll see ice-II, IV, V, VI, and now, for the first time, ice-VII.
However, this new form of ice represents a finding greater than the results of a simple increase in pressure. Ice-VII is unique in that it remains fairly stable even as the pressure continues to increase.
While this study documents the first time we’ve seen this new form of ice on Earth, scientists do believe that it may be found in larger deposits in areas such as the interior of ice moons like Enceladus or Europa – or even part of the ocean floor of Titan. The existence of ice-VII was theorized for quite some time, but no one ever thought that we would find it here on Earth.
While we now know that we can find ice-VII on Earth, it’s by no means easy to find. In order to reach the pressures required to form this new form of ice, you’d have to look deep into the mantle where the temperature is too warm for this ice to exist. What does allow ice-VII to form naturally, however, is diamonds.
Diamonds are capable of forming deep in the Earth’s mantle – sometimes as much as 400 miles beneath the crust. As they’re forming, they will occasionally trap pieces of the environment around them in “inclusions.” What is unique about diamonds is that the material trapped inside remains at the same pressure that it originally saw when it was formed into an inclusion, and this allowed us to see a diamond with ice-VII trapped inside as diamonds were pushed up to the surface.
Tschauner elaborated on this process to the LA Times:
“The diamond lattice doesn’t relax much, so the volume of the inclusion remains almost constant whether it’s in the Earth’s mantle or in your hand.”
George Rossman, a mineralogist at Caltech who also worked on the study, explained that “Usually the extremely deep minerals that come up to the surface are not stable once they experience low pressures…They crack and whatever inclusions they had in them are lost. But if a diamond comes up fast enough, it doesn’t change.”
As mentioned above, the mantle is too warm for this new form of ice to exist. However, the authors of the study recently discovered that diamonds are capable of trapping small bubbles of pressurized water when they form deep in the mantle. Then, as they rise towards the surface, the cooling temperatures allows ice-VII to form.
Since the discovery of ice-VII, it has now been recognized as a new mineral by the International Mineralogical Association.
For more information regarding the discovery process and the structure of ice-VII, check out the full study published in Science.