A natural shockwave event led to the formation of a new crystalline polymorph of carbon in gneisses from the Popigai crater, Russia. The new species occupies the interior of a multiphase assemblage and is entirely enveloped by lonsdaleite and graphite. Polishing hardness of this new phase is greater than that of lonsdaleite. Micro-beam synchrotron X-ray diffraction, imaging and fluorescence studies revealed a pure transparent carbon phase. The diffraction pattern is indexed in terms of a cubic cell ( a =14.697 Å, space group Pm3m .). This species was neither encountered in static or dynamic high-pressure experiment nor predicted by theoretical calculations.
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Goresy et al. (2003) studied this question.
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