Diamond is hard. It’s the hard man of minerals. It’s the hardest known naturally occurring mineral.
At least on Earth.
Now it looks like diamond may have met its match thanks to a meteorite that landed in Finland almost forty years ago. A team of scientists led by Tristan Ferroir studied a piece of the 1971 Havero meteorite and found something unusual. Their paper, published in the journal Earth and Planetary Science Letters, is called Carbon polymorphism in shocked meteorites: Evidence for new natural ultrahard phases. According to the abstract:
We report here the natural occurrences of one new ultrahard rhombohedral carbon polymorph of the R3m space group which structure is very close to diamond but with a partial occupancy of some of the carbon sites. We also report the natural occurrence of the theoretically predicted 21R diamond polytype with lattice parameters very close to what has been modelized. These findings are of great interests for better understanding the world of carbon polymorphs and diamond polytypes giving new natural materials to investigate. These natural samples demonstrate that the carbon system is even more complex than what is currently thought based on ab initio static lattice calculations and high-pressure experiments since this new ultrahard polymorph has never been predicted nor synthesized.
In other words: move over diamond, there’s a new hard man in town.