An international team of researchers say they’ve discovered the largest crystals to date of a rare type of diamond called lonsdaleite.

The diamonds have an unusual hexagonal atomic structure (compared with the more common cubic structure) and were found in a meteorite that may have originated from a dwarf planet that experienced a catastrophic collision with an asteroid billions of years ago. 

“This study proves categorically that lonsdaleite exists in nature,” Dougal McCulloch, director of the RMIT Microscopy and Microanalysis Facility in Australia, said in a statement.

The unusual hexagonal structure of the diamond could make it harder than most diamonds originating from Earth. Lonsdaleite has been found in a certain type of meteorite, called a ureilite, and it has even been manufactured in a lab by shooting graphite disks at a wall at speeds comparable with those of an asteroid impacting a planet. 

The research team looked at 18 ureilites, mostly from northwest Africa, and one discovered by Monash University geology professor Andy Tomkins on the Nullarbor, a vast, arid plain in southern Australia. The strange diamonds were found in just four samples, all from northwest Africa.

But the details of how these super-diamonds formed in space have remained somewhat mysterious. 

McCulloch and colleagues used advanced electron microscopy techniques to look at slices from the meteorites and think they may have discovered a new formation process for both lonsdaleite and regular diamonds. 

That process “is like a supercritical chemical vapor deposition process that has taken place in these space rocks, probably in the dwarf planet shortly after a catastrophic collision,” McCulloch said.