Ice Crystals Trapped in Diamonds Reveal New Form of Water, Ice-VII

We’re used to volcanoes spewing up magma and ash, but sometimes they’ll gush forth diamonds. And sometimes, those diamonds carry with them strange forms of matter from the deepest bowels of the earth, as researchers described in a Science paper on Friday. Their analysis of super-deep diamonds revealed a substance mysteriously named “ice-VII,” a high-pressure version of water that’s been created in labs and thought to exist in space, but has never been found on the surface of the Earth.

The presence of ice-VII, they explain in their paper, is evidence that small pockets of water flow deep underground in a transition zone of the mantle still considered a source of geological mystery.

As solid chunks of carbon arranged in a crystal lattice structure, diamonds are a looking glass for scientists searching for what’s going on deep within the Earth. During the diamond formation process, which happens hundreds of miles below ground, materials from the planet’s innermost layers can become encapsulated within the lattices. These “inclusions” are then preserved within the lattice at the same pressure they experienced at the time of entrapment. That’s why ice-VII is still preserved in these rare diamonds, like a photograph in a locket.

“Water in diamonds is not unknown, but finding this very high pressure form of water ice intact, that was really fortuitous,” co-author Geroge Rossman, Ph.D., told the Los Angeles Times. “That’s what you call a discovery.”

Analysis of the diamonds revealed they formed between 610 and 800 kilometers below the surface. It’s because of these extreme depths that the scientists are confident that they’ve found the first sign that unbonded water flows between Earth’s upper and lower mantle. Knowing that water moves around in this transition layer is important for scientists who study earthquake frequency, though they will have to shift geophysical models to reflect how this water flows through the tectonic plates.

The scientists used x-ray analysis on the diamonds — sourced from volcanic regions in Africa and China — to confirm the presence of ice-VII. Estimated to be one and a half times denser than the sort of ice we plop in a whiskey, the scientists never expected to find ice-VII in the diamonds: Originally, they wanted to find molecular forms of carbon dioxide trapped within the gems.

Instead, they found evidence of deep watery fluids and a form of ice that needs such an intense amount of pressure to exist that scientists never anticipated finding it naturally above the surface. Because of this study, the International Mineralogical Association has declared ice-VII a brand new mineral — a sign that while diamonds may be bling, what really matters is the ice.

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