Prospecting for Quasicrystals

Siberian journey nets a mineralogical space oddity

10:24am, October 19, 2012
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The rock came in a box labeled “khatyrkite.” It didn’t look like much, just a chunk less than a centimeter long with a whitish rind and studded with several dark metals. But when Paul Steinhardt got a good look inside, he saw something he’d been waiting years to see.

The quasicrystals nestled within displayed a bizarre symmetry that had never been seen outside the lab, an interlocking structure with no repeats. Steinhardt had been captivated by these almost-crystals since the early 1980s, when they were still a hypothetical form of matter.

But now, there they were.

Where had they come from? And how could Steinhardt get more of them? Those questions launched a three-year quest culminating in an expedition to one of the most remote parts of Siberia — and a scientific discovery that has yet to be fully revealed.

Typical crystals are crafted from repeating units of atoms. These structures, in their 2-D form, are shapes that when fit together could fill a space completely — like squares or hexagons. In contrast, the units in a quasicrystal, short for “quasiperiodic crystal,” are formed from units with symmetries that don’t occur in normal crystals (SN: 1/23/99, p. 60). The shapes can’t completely fill a space. If you were to tile your bathroom floor with, say, pentagonal pieces of just one size, you’d be left with gaps. You would have to use another shape as well. In the end, instead of a grid or honeycomb, your floor would look like the intricate mosaics decorating Islamic mosques and palaces.

It was the early 1980s when Steinhardt, working at the University of Pennsylvania with graduate student Dov Levine, began investigating what would come to be called quasicrystals. At the same time, a few hundred kilo­meters away, Dan Shechtman was actually making quasicrystals, albeit unintentionally. Shechtman would publish a paper describing the first synthetic quasicrystals in 1984, and win a Nobel Prize for them in 2011.

Since Shechtman’s discovery, more than a hundred quasicrystals have been synthesized in labs. Researchers suspected that the quasicrystals could be useful in electronics. But making them required idiosyncratic conditions such as an argon atmosphere, a vacuum and precisely controlled temperatures. No one knew whether the crystals could grow outside the lab, how strong they would be or how long they would remain intact. It seemed unlikely that quasicrystals could exist in nature.

Steinhardt wasn’t satisfied with that. “I wanted to find something that was much older than anything made by humans,” he says. “That would show that quasicrystals, like crystals, can be formed naturally and last a long time.”

Searching through catalogs and pulverizing mineral samples turned up nothing. So in 2001, Steinhardt, now at Princeton, published a plea in Physical Review Letters. He asked curators and scientists to canvass their collections for candidate samples.

Years went by, and Steinhardt had no luck. Then, in 2007, an Italian geologist named Luca Bindi came across Steinhardt’s request while browsing an old issue of PRL — an unlikely reading selection for a geologist. Bindi, who works at the University of Florence, offered to search through the collection of more than 10,000 mineral specimens at the university’s natural history museum.

There they found the khatyrkite. In 2009, Steinhardt, Bindi and colleagues announced in Science that the crumb of rock contained the first naturally produced quasicrystals ever uncovered.

Finding Kryachko

What the Science paper couldn’t say was where exactly the khatyrkite and the quasicrystals within had come from.

While the box pointed to Russia’s Koryak Mountains, the researchers couldn’t be sure. And they wanted to know if they could recover more chunks from the same area. They needed to find the person who found the rock.

That search turned into more than a year of dead-ends and misinformation — an investigation that Steinhardt and Bindi agree is way too complicated for a simple retelling. “It involves looking for missing persons, it involves finding some secret diaries, it involves looking for a strange Romanian smuggler, getting involved with someone who was either KGB or strongly KGB-connected, death threats to some of our people,” Steinhardt recounts. “All kinds of blind alleys.”

Finally the team managed to identify geologist Valery Kryachko, now in his 60s and working for a private company in Russia. Kryachko told them he had plucked the fragment from the Listvenitovyi Stream during an unsuccessful platinum prospecting trip in 1979. He didn’t know until Steinhardt and Bindi tracked him down three decades later that the unusual chunk harbored something even more rare than platinum.

“What is tremendously fascinating for me is that Valery had in his hands the Florence sample, containing the first natural quasicrystal in 1979,” Bindi says.

From there, the rock had gone on its own journey. Smuggled out of Russia in the 1980s, it eventually reached a collector in Amsterdam, who in 1990 sold his entire collection to the Florence museum. There it sat until becoming the inspiration for Bindi and Steinhardt’s Siberian odyssey.

It came from space

While tracking down Kryachko, the pair was also trying to figure out how the mystery rock had formed. Was it of terrestrial origin, or a fragment of a meteorite? Could it be artificial, perhaps the by-product of some industrial process?

When Steinhardt described the rock to Lincoln Hollister, the Princeton petrologist noted that the quasicrystal component of the fragment contained metallic aluminum in an oxygen-free form that is impossible to find naturally on Earth.

“When you say impossible, do you mean really, physically impossible or do you just mean very, very unlikely?” Steinhardt recalls asking Hollister.

Very unlikely, it turns out. Oxygen-free aluminum could live thousands of kilometers beneath the Earth’s crust, near the core-mantle boundary, Hollister said, but getting it to the surface would be problematic.

So Steinhardt looked skyward. At first, an extraterrestrial origin seemed improbable, but analyses conducted in 2010 did point to the stars.

In one part of the sample, the team found a bit of quasicrystal cocooned within a grain of stishovite. A naturally occurring, glassy compound, stishovite forms only under pressures 100,000 times greater than those on the Earth’s surface — during an asteroid-on-asteroid collision, for example. That was the strongest evidence for an extra­terrestrial origin for the quasicrystal, Bindi says.

The forms of oxygen in the sample, described earlier this year in the Proceedings of the National Academy of Sciences, clearly identified the rock fragment as a CV3 carbonaceous chondrite, coming from an asteroid born during the earliest days of the solar system, 4.5 billion years ago. But to prove that the quasicrystal, not just its rocky shell, was extraterrestrial, Steinhardt and Bindi needed Kryachko to take them to the rock’s original resting place. “I decided that a trip to Chukotka was called for,” Steinhardt says.

Panning for meteorites

In July 2011, Steinhardt and Bindi rendezvoused with their team in Anadyr, capital of Siberia’s Chukotka region. Bordered in the north by the Chukchi and East Siberian seas, and by the Bering Sea in the east, the region is the part of Russia nearest to the United States. Getting into a longtime strategic defense zone meant using some creative language to convince the government, and military, to cooperate. “It’s not the usual story of getting a Russian visa,” Steinhardt says.

The plan was to head to the site in the Koryak mountains where the rock had first been found. Striking out overland meant embarking on a 350-kilometer journey atop spongy, shape-shifting tundra that’s tricky to walk on, let alone drive over. Vehicles looking like minivan cabs parked atop tanklike treads carried the 13-person team deep into the mountains, through air thick with mosquitoes, streams packed with salmon and landscapes teeming with grizzly bears.

“I’m used to working in places that have things that try to eat you,” says geologist and team member Chris Andronicos of Purdue University in West Lafayette, Ind. “I think that’s also part of the reason I was recruited.”

After four days, the team left the vehicles behind and backpacked another 1.5 kilometers. Here, Steinhardt would try to dig up his newest targets — sirenlike shards that seem to have been calling to him since he first started studying quasicrystals.

Once near the stream, Kryachko took an afternoon to identify the spot where he’d recovered the original meteorite more than 30 years earlier. “Valery is an amazing person,” Andronicos says. “I would’ve really loved to have been able to talk to him without a translator.”

Andronicos, brought along to survey the region for the unlikely presence of a terrestrial quasicrystal factory, went to work scampering up local peaks. Rising a few hundred meters above the surrounding terrain, the Koryaks, though a popular destination for prospectors, are relatively unmapped. After exploring, Andronicos concluded that the quasicrystal was unlikely to have been produced locally.

Meanwhile, the others were mining the stream for meteorites. Though Listvenitovyi Stream is small, about 3 meters wide and 40 centimeters deep, the task turned out to be more complicated than expected. Clays at the stream’s bottom were so heavy that they broke the team’s shovels in less than 20 minutes, leaving the researchers digging up 1.5 tons of cold sludge mostly by hand.

But the sludge yielded a few potential meteoritic chunks — black and shiny, and only several milli­meters across. “I observed a very promising grain the very first day,” Bindi says. But on the way back home, no one believed there was any higher than about a 1 percent chance that they had found any pieces from the original meteorite, Steinhardt recalls.

“It was a major, major find when … we found our first example of a grain that was clearly meteoritic,” says Steinhardt. “It also had grains of a metallic phase that proved to be another example of quasicrystals. It was identical.”

In all, Steinhardt says, he has nine more meteoritic samples, a find reported in September in Reports on Progress in Physics. Now, the researchers are studying these additional space crumbs, looking for and analyzing quasicrystals within. “This is a very exotic material, indeed,” Bindi says. Though they won’t disclose the newest results, team members promise the tale just gets weirder.

“I am certain this study will produce more than just a description of a mineral sample,” says Robert Downs, a geologist at the University of Arizona who is familiar with the story. Downs notes that, because of their age and composition, there is a tantalizing possibility the meteorite’s quasicrystals were born from a shock wave that swept through the dusty early solar system, the rippling product of a nearby supernova that eventually triggered the formation of the sun and planets. Ongoing analyses of these samples, he says, “will tell us something fundamental about the process that created the material that formed our solar system.”

Though they’re making the world wait a little bit longer to find out more, one thing is clear: Steinhardt and Bindi have shown that quasicrystals aren’t just finicky, lab-grown oddities. The most extreme circumstances in nature can also create them, and they can endure for a long, long time.

“Our goal originally had been to find something fairly old, older than the last century, at least,” Steinhardt says. “We overshot the mark. These are 4.5 billion years old.”

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