Otherworldly ice found in diamonds

Trapped in the rigid structure of diamonds formed deep in the Earth’s crust, scientists have discovered a form of water ice that was not previously known to occur naturally on Earth.

The finding, published Thursday in Science, represents the first detection of naturally occurring ice-VII found on Earth.

Ice-VII is about one and a half times as dense as the ice we put in drinks and skate on, and the crystalline structure of its atoms is different as well. In normal ice, known as ice-I, the oxygen atoms arrange themselves in a hexagonal shape. In ice-VII these atoms are arranged in a cubic shape.

Oliver Tschauner, a professor of geoscience at the University of Nevada, Las Vegas, explained several phases of water ice form under different pressure and temperature conditions. Generally, when you subject a solid phase of matter to increasing amounts of pressure, the space between the chemical bonds will decrease, and the bonds will tilt toward each other, said Tschauner, who led the new work. That’s called compressibility.

But water ice has low compressibility and when it’s subjected to too much pressure, the atoms don’t scooch together. Instead, they rearrange themselves into different patterns.

Scientists believe that ice-VII may be found in great abundance in the solar system. But they did not think it could naturally occur on Earth. The pressures ice-VII requires to form can be found only deep in the mantle where the temperature is too warm for this form of ice to be stable.

The new study revealed small amounts of ice-VII can form naturally on Earth, thanks to the peculiar properties of diamonds.