A team of Chinese scientists may have cracked the secret behind the strange Canyon Diablo diamonds. Hexagonal in form rather than cubic, the process behind how these diamonds formed has, until now, remained elusive.
Diamonds are usually made of carbon atoms in a cubic arrangement (like stacked Lego blocks in a cube pattern). But there is a rarer form, the hexagonal diamond (atoms stacked in a honeycomb-like pattern), that seems to originate when meteorites smash into Earth, producing extreme heat and pressure.
The very first hexagonal-structured diamond was found within the ‘Diablo Canyon’ meteorite which is believed to have hit the Earth about 50,000 years ago and landed in what is present-day Arizona.
Now, a joint team of experts from the Centre for High Pressure Science and Technology Advanced Research and the Chinese Academy of Sciences’ Xian Institute of Optics and Precision Mechanics have claimed to have recreated the enigmatic ‘meteorite diamond’ in a laboratory.
Cracking the meteorite’s secrets
Most diamonds are forged nearly 90 miles (150 kilometers) below the Earth’s surface, where temperatures can reach more than 2,000 degrees Fahrenheit (1,093 degrees Celsius). The temperature and pressure at this depth causes carbon atoms to arrange themselves into cubic shapes.
In contrast, the Diablo Canyon meteorite contains a series of strange, alien diamonds formed during its violent path to Earth. The diamonds found inside the meteorite have a hexagonal crystal structure called lonsdaleite. This crystal structure makes the diamonds even harder than ‘traditional’ ones, perhaps by as much as 60%.
Since their discovery, there has been a decades-long debate about whether meteorite diamonds actually exist in pure form, or if these tiny crystals are just mixed phases of cubic diamond and graphite.
Earlier attempts at finding answers usually ended up making ordinary cubic diamonds or messy mixtures. For example, a team was partially successful in synthesizing them using gunpowder and compressed air on graphite disks. However, the Chinese team’s success appears to have now settled a 60-year scientific argument.
Synthesizing alien diamonds
According to reports, the team managed to make pure hexagonal diamond crystals which are 100 micrometres in width, or about the thickness of a strand of human hair. This was achieved by using extremely pure, single-crystal graphite with the idea that fewer impurities would mean less chance of ‘defaulting’ to the cubic structure.
Using this, the scientists applied controllable high pressure and temperature, plus quasi-hydrostatic conditions (meaning the pressure is uniform in all directions). They also used in-situ X-ray techniques during the process to observe the transformation real time and adjust conditions to favor hexagonal diamond growth.
The breakthrough is being touted as the first macroscopic proof that hexagonal diamond really exists as a distinct, stable structure. It also pushes the limits of what ‘superhard’ means, beyond the properties of a traditional cubic diamond.
Considering that the new synthetic hexagonal diamond promises superior hardness and thermal resistance, its could be used in manufacturing cutting tools, wear-resistant coatings, and possibly high-end electronics (diamonds are excellent thermal conductors and can handle extreme conditions).
“This synthesized hexagonal diamond is expected to pave new pathways for the development of superhard materials and high-end electronic devices,” stated Ho-kwang Mao from the Chinese Academy of Sciences.
The study has been published in the journal Nature.
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