“I hope this paper prompts more theoretical and modeling studies in this area,” she adds.ĭominik Kraus, a high-energy-density physicist at the University of Rostock in Germany, who was also not involved in the study, feels similarly. “I think the formation method presented here is logical and may be one possible pathway to form this material, but I admit I am not 100 percent convinced,” says Jodie Bradby, who researches high-pressure physics at the Australian National University but was not involved in the study. Outside researchers note that this is only one potential explanation for the presence of lonsdaleite in these meteorites. Plus, the samples contain interlocking layers of lonsdaleite, cubic diamond and graphite in a pattern that points to the fluid-driven transformation Tomkins’s team describes. Looking at particular radioactive signatures of the minerals, the researchers estimated a date for this collision-roughly 4.5 billion years ago. Tomkins explains that the structure of these meteorites’ minerals indicates a rapid cooling process that points to a dramatic collision. The researchers landed on this lonsdaleite origin story through painstaking analysis of their 18 ureilite samples. And much like escape vessels from the planet Krypton, those chunks eventually carried their precious cargo all the way to Earth. This fluid-driven reaction took place in chunks of the dwarf planet as they went flying into space. “It’s called ‘coupled dissolution-reprecipitation’ because it’s kind of dissolving this thing and replacing it at the same time,” Tomkins says. In this particular reaction, graphite crystals would have been essentially torn apart and rebuilt into lonsdaleite. Study co-author Andrew Tomkins, a geologist at Monash University in Australia, says that the rapidly depressurizing mix of chemicals could have interacted with the dwarf planet’s graphite to transform it into lonsdaleite. They claim that a fluid mix of carbon, hydrogen, oxygen and sulfur was heated and pressurized in the dwarf planet’s mantle until an asteroid impact smashed that mantle into pieces. The researchers propose that rather than the rapid impact pressure known to produce tiny lonsdaleite crystals on Earth, these samples instead formed through a rapid release of pressure. But a brief period of extremely intense pressure-such as that of a meteorite impact-can preserve graphite’s original hexagonal arrangement while its layers bond into the strong 3-D lattice of lonsdaleite. On Earth, high heat and pressure can rearrange these carbon atoms into a 3-D lattice of cubes, thereby creating the traditional kind of diamond. These stacked layers are weakly attracted to each other and relatively easy to pull apart. Graphite is made up of flat layers of carbon atoms bonded together as hexagons. This cataclysmic impact tore the dwarf planet apart, sparking a chemical reaction that could have turned pieces of the planet’s graphite into lonsdaleite, he adds. “There was this dwarf planet just after the start of our solar system-so 4.5 billion years ago-and the planet got hit by an asteroid,” says Alan Salek, a graduate student in applied physics at the Royal Melbourne Institute of Technology in Australia and co-author of the new study. If the team’s theory of the crystals’ formation is correct, its findings could offer scientists a better way to manufacture the ultra hard substance on Earth.įor a study published this month in the Proceedings of the National Academy of Sciences USA, the research team, primarily based in Australia, examined 18 different meteorite samples from a family known as “ureilites.” Because ureilites are relatively homogeneous in their chemical composition-which is uniquely rich in carbon- scientists theorize they originate from the same parent body. But now researchers say that they’ve identified lonsdaleite crystals that formed billions of years before the meteorites carrying them ever reached the planet. To date, natural lonsdaleite has been found only in impact craters, where it has formed by the intense pressure of meteorites crashing to Earth. Yet a rare form of diamond known as lonsdaleite-a crystal with carbon atoms arranged in flexing three-dimensional hexagons-may be even harder than its cubic cousin. Diamond, with its tough-to-break carbon lattice of interlocking cubes, is traditionally considered the hardest material on Earth.
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