Researchers at the Université de Lyon in France, have discovered what appears to be an unexpected new form of ultrahard diamond and a new ultrahard form that was previously predicted, both harder then commonly found diamond. These forms were found in the Havero meteorite, which fell to earth in Finland in 1971. The meteorite was split up and spread around research facilities around the world, with the Université de Lyon conducting research on the 30µm thick, 4mm by 4mm square piece of meteorite they were given.
The new phase of carbon was uncovered after researchers cut and then polished a thin section of the meteorite, only to find areas rich in carbon to be protruding from the surface. These areas are small but strong as they were able to withstand the polishing from the diamond paste. The conclusion was that since the areas are formed from carbon this would mean a new phase in which ordinary diamond was no match in hardness. These findings were published in Earth and Planetary Science Letters, titled "Carbon Polymorphism in shocked meteorites: Evidence for new natural ultra-hard phases".
The research aim of the team was to investigate shocked meteorites for new phases of the carbon system, as previous research by El Goresy et al., 2003 had discovered new phases previous in similar meteorites. A shocked meteorite is one in which its parent body has undergone a large impact, most likely from another large body. These shocks can generate enough pressure and energy at a high temperature for the meteorites parent body to form veins of diamond and graphite, especially when the size of the bodies involved can be up to 100km in size. However, "it is a debate whether the diamond formed in this meteorite were of shock origin or if they were formed by Chemical Vapor Deposition.” said Tristan Ferroir, the lead author of the research. Chemical Vapor Deposition (CVD) is a chemical process in which diamond can be grown, by ionising chemicals to encourage them to form the desired material.
When the shocked meteorite was studied using optical microscopy the raised areas unpolished by the diamond paste stuck out to heights of 13µm. With chemical mapping through the use of x-ray fluorescence and x-ray diffraction, the scientists were able to discover that the areas were of low density, suggesting the area consisted of mostly carbon.
When Raman spectroscopy was used on this area it was discovered that the area of the meteorite resistant to the polishing composed of diamond graphite, but also of many additional properties. The spectroscopy discovered that the material shared spikes in the bands with other forms for carbon, such as diamond and graphite, but also spikes that are not associated with any other phases of carbon.
Tristan Ferroir told me the area “... is made of either the new phase or the 21R polytype of diamond mixed with graphite and diamond. But some of these peaks are not attributed to any known carbon compounds, which is indicative of a new phase. That's why we followed our investigation by other measurement and confirmed that it was indeed a new phase.”
So far, however, the samples are too small to have their strength tested against harder artificial diamonds, as the crystal size is believed to be only around 1µ, and unfortunately the other samples were already prepared for other experiments. If greater sizes of these diamonds were found, their hardness could be tested by literally impacting them onto ordinary diamond, to see if they cause any indent on the diamonds surface.
When asked the future implications of these new naturally occurring forms of diamond, Tristan Ferroir stated that it depends on the possibility of synthesising the diamond, and how much synthesis would cost, especially since the synthesis of artificial diamonds use high pressures, and are very expensive. Is it possible that many more meteorites contain veins of these naturally occurring ultra-hard diamonds? It's possible future discovery of shocked meteorites could discover even more new forms of the carbon phase.
