The first discovery of a large diamond of the “CLIPPIR” group in the alluvial deposit Ebelyakh (Yakutia)

Russia is the leader in the diamond mining industry among all countries of the world but finds of large diamonds over 50 carats of gem quality are very rare for its deposits. For example, the 342.5 carat XXVI Congress of the CPSU diamond was recovered in 1980 from the Mir kimberlite pipe and is still the largest gem-quality diamond mined in Russia. In 2023, a 390.65 carat gem-quality diamond fragment was discovered at the Ebelyakh alluvial deposit (Western Yakutia). The modelled 3D-reconstruction of the whole diamond crystal made it possible to assume that in terms of shape it was a dodecahedroid elongated along the L3 axis, the mass of which was about 1500 carats — this is the largest gem-quality diamond fragment found in the history of diamond mining in Russia. This article is the first to present the results of a comprehensive study of a large diamond fragment weighing 390.65 carats. The research was carried out in the Gokhran of Russia and ALROSA using the methods of optical microscopy, photoluminescence and infrared spectroscopy. The detected inclusion in diamond was studied by Raman scattering. It was determined that the diamond belongs to type IIa according to the physical classification and has a single small inclusion in its composition belonging to the sulfide association. It was established that the studied diamond can be attributed to the CLIPPIR group of diamonds according to the totality of features. The authors tried to establish the regularities of formation of this diamond.