Lab-made diamond harder than the natural gem

Diamonds are the hardest minerals known to humankind – with the ability to cut steel and the most impenetrable rock.

However their place at the pinnacle of the Mohs scale – which compares a mineral's hardness by its ability to visibly scratch other minerals – could be in jeopardy according to recent research by scientists at Australian National University.

Using a device called a diamond anvil cell, which squeezes two diamonds together at extremely high pressure, the researchers created a diamond at just over 400 degrees Celsius, according to posts in scientific site Phys.org and science blog Science Alert. The research has been published in Scientific Reports.

The diamond the researchers created is a nano-scale version of lonsdaleite, which occurs naturally at a handful of meteorite impact sites around the world such as Canyon Diablo, Arizona. The heat and stress resulting from the strike transforms graphite into diamonds while retaining graphite’s hexagonal crystal lattice.

"The hexagonal structure of this diamond's atoms makes it much harder than regular diamonds, which have a cubic structure," lead researcher Jodie Bradby told Phys.org. "We've been able to make it at the nanoscale and this is exciting because often with these materials 'smaller is stronger'."

Named after Irish crystallographer Kathleen Lonsdale, lonsdaleite is estimated to be 58 percent harder than natural diamonds. The research team was able to nano-engineer the diamond from scratch using amorphous carbon.

According to Science Alert, researchers have managed to make londaleite in laboratories before, but without much success, considering it normally requires temperatures of about 1,000 degrees Celsius.

In terms of applications, Bradby says the lab-made lonsdaleite is more likely to be used for cutting through super-hard materials at mine sites, rather than in jewellery.