For decades, lonsdaleite has been something of a philosopher’s stone for geologists. Hard as a diamond (if not harder), the very existence of this “super crystal” had been called into question. Until an international team not only managed to prove its existence but also point out its possible extraterrestrial origin.
A 55-year-old mystery. Lonsdaleite was initially discovered in 1967 in Barringer Crater, a geological structure located in Arizona and formed 50,000 years ago after the impact of a meteorite. In it they found the material which they named in honor of the crystallographer Kathleen Lonsdale, the first female member of the Royal Society of London.
Confirmed. But confirmation of the discovery would take half a century to arrive. The reason is that many believed that lonsdaleite did not exist as such, but was a strange, anomalous form of a known mineral: diamond. Both are allotropes of carbon, that is, elemental carbon intertwined in different structures: diamond in cubes and lonsdaleite in hexagons.
More evidence was needed that these crystals corresponded to a new mineral. Last year, an article published in the journal Proceedings of the National Academy of Science, signed by an international team of scientists from different research centers, shed light on the matter.
Closer to the answer. The work pointed to lonsdaleite as a very real mineral. The enigma was solved thanks to two factors. The first, that the samples we have are much larger than those we knew until now, on the order of 1000 times larger. The second is the technical development in recent decades, which has given us an improvement in microscopy devices.
In the words of Paul Asimow reported by CNN, the professor of geology and geochemistry at CalTech (who was not involved in the recent study) explained that “you really need to take advantage of a number of recent developments in microscopy to do what you want.” [los investigadores] have done and as well as they have done it.
Not unlike a diamond. Despite their structural difference (which makes the new mineral even harder than diamond), the two minerals, diamond and lonsdaleite, would be formed in a similar way, through one of three processes. They can appear when carbon is exposed for long periods of time under high pressure and high temperatures. This is the way diamonds typically form on the Earth’s surface.
These minerals can also form after a blow, a shock, such as the collision of a meteorite. And the third mechanism through which they would be formed would be the vapors released from graphite, whose atoms would “stick” to an existing piece of diamond, making it grow in size.
A dwarf planet in our environment. The authors also pointed out in their study the origin of this mineral. Unlike diamonds, the origin of lonsdaleite would be extraterrestrial and would be derived not from high pressures and temperatures but from an impact. This impact would have destroyed, about 4.5 billion years ago, a dwarf planet in our solar system. This event would have occurred approximately at the time when our planet was formed.
A discovery with applications. The “new” mineral could replace diamond in some of the applications where its hardness is key. Mining would therefore be the sector where the potential of this material could be exploited. To do this it will be necessary to find ways to synthesize it as can already be done with diamond. Hence the importance of this step when it comes to understanding the nature of this mineral and, above all, having managed to decipher its origin.
“Nature has provided us with a process to try to replicate in industry. We believe that lonsdaleite could be used to make small, ultra-hard machinery parts if we can develop an industrial process that promotes the replacement of preformed graphite parts with lonsdaleite,” he noted. Andy Tomkins, one of the team’s researchers.
A rare mineral, some frequent enigmas. It may seem strange to doubt the existence of something tangible, but the truth is that analyzing and cataloging what we find in nature does not have to be an easy task. Geology and materials physics still hold mysteries for us to solve.
We are still discovering minerals, and space exploration has a lot to do with it. Lonsdaleite, for example, is not the only mineral that we theorize about before we can ensure its existence. Only time and technological advancement will be able to determine whether the promises posed by this new mineral materialize.
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Image | RMIT University
*An earlier version of this article was published in September 2022