Despite its popularity on Earth and presence throughout the galaxy, there’s still a lot of mystery about diamonds. Now scientists have found new insights about the origin of diamonds in stony meteorites known as ‘ureilites’. They claim the diamonds most likely originated due to rapid shock transformation from graphite.
Graphite is the most common low-pressure form of pure carbon. The shock can be attributed to multiple or (single major) impacts on the parent ureilite asteroid in the early stages of the solar system.
The former belief about ureilite’s diamonds suggested that they formed deep within the mantle, just like they do on Earth. The deep mantle is a highly pressurised ore, so the conditions would be optimum for diamond formation. There, the dense, hard form of pure carbon- diamond- could be created by the weight of overlying rocks. If this theory were true, then the original parent body of ureilites must have been large, a protoplanet of sorts, competing with the size of Mercury or even Mars!
But the new research suggests otherwise. Dr Cyrena Goodrich of Universities Space Research Association at the Lunar and Planetary Institute and Prof. Fabrizio Nestola of University of Padova, Italy, led this study on ureilites. Their evidence suggests that there is no proof of high static pressure or long growth time conditions of a planet’s deep interior, as reported on PRNewswire.
Their research was carried out on three ureilites samples. They used micro X-ray diffraction, electron microscopy and Raman (laser) spectroscopy to analyse the rocks. They discovered large and small grains of diamonds ranging from 100 micrometres to a few nanometres in size. They also revealed graphite and metallic iron in the carbon-rich regions located among the silicate mineral grains in these samples.
Dr Goodrich suggested one of the diamonds observed was the largest single-crystal diamond ever found 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,” she added.
The study gives important implications as it not only refutes that these asteroids had planet-sized bodies but also establishes that the diamonds were formed due to shock-force in a very short span of time. These findings have important implications for models of planetary formation in the early solar system.