On Earth, diamonds form deep underground, under immense pressure. And scientists thought the same was true for a particular type of meteorite – ureilites.

Of course, for this formation process to be true, these meteorites would have had to come from pieces of a much larger body in order to create the amount of pressure needed to compress carbon into diamonds. Think of a protoplanet the size of Mercury or Mars.

Now, however, researchers from the University of Padova and the Lunar and Planetary Institute (LPI) examined various ureilite samples and found evidence for a different origin. Dr. Cyrena Goodrich explains: We discovered the largest single-crystal diamond ever observed in a ureilite. Importantly, the ureilites that we investigated have all been highly shocked, based on the evidence from their silicate minerals, which strongly suggests that both large and small diamonds in these rocks formed from original graphite via shock processes.

Shock processes like an impact. This means that the prevailing theory of protoplanet formation on a Moon- to Mars-like scale is not required for these meteorites and their parent asteroids. And that, once again, changes how we create our formation models.

More Information

LPI press release 

“Impact Shock Origin of Diamonds in Ureilite Meteorites,” F. Nestola, C. A.
Goodrich et al., 2020 Sep. 28, Proceedings of the National Academy of
Sciences