Pop quiz: what is the world’s hardest material?

Answer: it’s diamond, of course.

Thanks to the crystal structure of diamonds, with carbon atoms arranged into a lattice-like structure, diamond is top of the hardness scale, which is why it is used to cutting and drilling, as well as in research and medical devices.

The incomparable qualities of diamond make them precious for many more reasons than just the centre stone on your engagement ring.

For a long time, we fully believed that of all the substances on our planet, diamond was the hardest.

And that’s still partly true – however, thanks to scientists from China, a new material even harder than diamond has been created.

To the untrained eye, this alternative material – known as lonsdaleite – would look just like a diamond. However this substance, whose only previous presence on Earth was in meteorite debris in Arizona, actually differs from diamond in several ways.

Primarily, the bonds between carbon atoms form a hexagonal structure, with more bonds meaning an even stronger and harder substance.

Thanks to the massive impact of the meteorite, sufficient force caused lonsdaleite to form, instead of the diamonds that might previously have been expected.

And with the knowledge of lonsdaleite formation in mind, scientists in China recently decided to try to synthesise lonsdaleite. While this has been done in the lab before, the process was inefficient.

In their paper, recently published in the journal Nature Materials, the research team determined to prove once and for all whether human processes were sufficient for the creation of those all-important hexagonal carbon bonds, without the surplus production of additional carbon-based materials like graphite and diamonds too, as they explained in the paper.

“With potentially superior mechanical properties and an intriguing structure, lonsdaleite has also received intense research interest in materials science. Theoretical calculations suggest that HD [hexagonal diamond] may even surpass cubic diamond (CD), the hardest and least compressible material known in nature today.

Theoretical calculations suggest that the total energy of CD is a little lower than that of HD, and that, when starting from the graphite precursor, the energy barrier of the direct graphite-to-CD transition is slightly lower than that for the graphite-to-HD transformation, and thus CD has usually been the dominant product.”

With understanding of the conditions required to form lonsdaleite, the team recreated the material’s optimal temperature and pressure requirements, as they continued:

“To overcome such unfavourable factors for HD growth, we synthesized HD from graphite via intermediate post-graphite phases in which interlayer bonding may lock a near-AB stacking in the compressed graphite and hinder the further sliding of layers during high-temperature stimulation, favouring the formation of HD. Both our experiments and simulations indicate that, besides the formation of the post-graphite phase, the presence of a temperature gradient is also critical for HD synthesis.”

The result? An impressive haul of lonsdaleite (here known as hexagonal diamonds).

Why is this important? Well, even though diamond (or, cubic diamond) is an incredibly useful substance, it does still have its limits.

And in terms of its hardness and pressure resistance, lonsdaleite surpasses the qualities of its cubic cousin; thanks to its hexagonal carbon bonds, lonsdaleite can take significantly higher pressures than diamond before it breaks, with its hardness 58% more than even diamond, leading to the possibility of better tools and implements.

While lonsdaleite is rare – unlike diamond, which can be mined or lab-grown, until now lonsdaleite has only been discovered in craters – the possibility of lab-made lonsdaleite launches research, science, industry and medicine into the future.

Because, thanks to the Chinese research teams, it is clear that under the right conditions, this super-hard material can be formed right here on Earth.

If you thought that was interesting, you might like to read about why we should be worried about the leak in the bottom of the ocean.