” When a meteorite containing graphite crashes into Earth, the heat and pressure of impact can turn this carbon formation into a rare and extremely hard type of diamond ” said to hespress.fr, the Moroccan meteorite expert, the doctor in mineralogical petrology (Pierre and Marie Curie University, Paris) and professor at the Faculty of Sciences, Agadir, Abderrahmane Ibhi.
Moroccan researchers from the University Museum of Meteorites, Ibn Zohr University, including Professor Ibhi and their Italian counterparts from the Institute of Crystallography and the Institute of Plasma Science and Technology, looked at a rare family of meteorites ( primitive achondrites; 0.6% of all falls) which are called Ureilites. Well they took it, since at the end of their experience the discovery was of size… of a diamond one would dare to say.
Fragment of Ureilite, NWA 12606 (polished section) © UMU.
They are quite unusual stony meteorites compared to other known stony meteorites. They take their name from the village of Urey, Republic of Mordovia in Russia, where a meteorite of this type fell on September 4, 1886. Until recently, it was completely unknown what type of parent body they could be associated with. For Moroccan-Italian researchers, this eliminates the fact that these diamonds are synthesized inside a large asteroid. Further scientific research on this topic and analysis by other techniques is needed to further study the sample to reveal the nucleation and growth history of these valuable phases.
It should also be mentioned that this meteorite was exhibited for more than two years at the University Museum of Meteorites of the Ibn Zohr University. The latter currently contains about 120 meteorites, noting that the number of Moroccan meteorites in international museums is estimated at 1,700 samples (includes more than 37 meteorites from Mars and a large number of lunar and carbon meteorites). The objective of the creation of this meteorite museum is to provide extraterrestrial material to Moroccan and foreign scientists and also to preserve this heritage for future generations. Unfortunately in most countries of the Arab world, the common culture does not appreciate the scientific value of such rocks, and some try to profit from them by offering them for sale abroad, whereas it is natural that ‘they are placed in a museum and / or in a scientific research laboratory.
Microphotograph of Ureilite NWA 12606 showing areas of graphite and diamond surrounded by silicates (Olivine and pyroxene). © MUM.
Meteorites are “messengers” of the Solar System, not only they bring us distant samples, but also ancient samples. In this respect, the meteorite “NWA 12606” is particularly important. This 197 gram alien rock, found in 2018 about 30 km southeast of Midelt, in the Draa Tafilalet region (Morocco, approximate coordinates of 32 ° 39′08.7 ″ N, 4 ° 41′42.6 ″ W), is considered among the oldest objects in the Solar System. It would have formed almost four billion six hundred million years ago, at the same time as the planets and the Sun itself. This rock was recently classified in the Ureilite group. Initial petrography for classification noted an approximate modal abundance of 90% olivine, 5% pyroxene, and 5% graphite. Two polished thin sections of this meteorite were prepared, one to analyze the petrographic and mineralogical characteristics of the silicate and carbon phases by light microscopy and the second thin section is prepared for the scanning electron microscope (SEM) analysis of the Faculty of Sciences of Agadir. The latter has been subjected to a gold metallization process to avoid any carbon contamination.
Micrograph of Ureilite NWA 12606 showing areas of graphite and diamond. © MUM.
Carbon was typically present between millimeter-sized olivine and pyroxene crystals, sometimes even inside these silicate minerals. The detailed petrology-mineralogical study of ureilites shows that the impact mechanism is dominant for the formation of diamonds, which is confirmed in this study by the presence of undulatory extinction of olivine and shock veins (showing violent impacts of small celestial bodies). High pressures and temperatures (above 30 GPa and 2000 ° C) are required for the shock wave (propagating from the place of impact) to transform the solid phases of graphite into diamond. Therefore, during a shock event, graphite can turn into large diamonds if metals (Fe-Ni) are present and if the shock event is long enough to allow the diamond to grow (a few seconds as shown for the shock event that destroyed the parent body of ureilitis).
In conclusion of this study published in a journal of the scientific academy founded since 1603 and which brought together certain scientists who have contributed to the history of Sciences in the world, in particular Galileo Galilei, Charles Darwin, Albert Einstein and Louis Pasteur, suggests that the meteorite collected in the region of Midelt (Morocco) underwent an intense shock metamorphism, and the graphite assumed to be the original carbonaceous material, could be partially transformed into diamond by the shock impact caused by a collision of the body parent in space.
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