The first discovery of hydrated magnesium carbonates, dypingite and nesquehonite, in the kimberlite pipe Obnazhennaya of the Kuoyka field, the Yakutian kimberlite province is described. The pipe is composed of kimberlite breccia with abundant diverse xenoliths of practically intact mantle rocks. Olivine in phenocrysts and mantle rock is generally intact. The main body of the rock is carbonate-serpentine. Nesquehonite and dypingite are rare minerals and have first been observed in relation to kimberlites. The minerals were found in the bedrock outcrop of the Obnazhennaya pipe as white crusts up to 5 mm thick scattered over an area of a few tens of square meters. To identify and study the crusts we used the following methods: powder X-ray diffraction, electron microscopy, and Raman scattering spectroscopy. A comprehensive study suggests that the main minerals of these epigenetic formations are hydrated carbonates: nesquehonite MgCO₃3H₂O and dypingite Mg₅(CO₃)₄(OH)₂5H₂O. Also, Raman scattering spectroscopy revealed a small proportion of hydromagnesite Mg₅(CO₃)₄(OH)₂4H₂O. Hydrated magnesium carbonate minerals we found make a significant contribution to the collection of kimberlites. They are epigenetic in nature, with their origin being related to weathering of silicates, in particular serpentine. Mechanisms of carbonate formation appear to be close to that suggested by Wilson et. al., 2009, with CO₂ being trapped from the atmosphere to form nesquehonite. In the case of the Obnazhennaya pipe, mineral solutions form when rainwater filters through the talus at the top of the outcrop. They are enriched in Mg from minerals and trap CO₂ from the atmosphere. After filtering, solutions reach the vertical wall of kimberlite breccia where modern precipitation of nesquehonite upon evaporation occurs. Further, dypingite and hydromagnesite form via decomposition of nesquehonite. A lip extending over the rock wall significantly contributes to the development and stability of nesquehonite and dypingite aggregates. Crusts of nesquehonite and dypingite are not found on rock outcrops without lips at the top. Thus, despite the fact that intrusion of the kimberlite pipe occurred during the Jurassic (Zaitsev, Smelov, 2010), formation of nesquehonite and dypingite in association with kimberlite rocks continues in the modern time due to favorable environmental factors, first of all, a unique natural outcrop of kimberlite.

The result of a complex mineralogical study of the first discovery of the rare hydrated magnesium carbonate minerals of Nesquehonite and Dypingite in the Obnazhennaya kimberlite pipe (of the Yakutian kimberlite province) is presented. The methods of X-ray phase analysis, electronic microscopy, and Raman spectroscopy have established that the main minerals of the samples found in the form of white crust on a small area of rock outcrop of kimberlite breccia are hydrated carbonates: Nesquehonite is MgCO₃•3H₂O, Dypingite is Mg₅(CO₃)₄(OH)₂•5H₂O. The formation of Dypingite over Nesquehonite was shown using Raman imaging for the first time. Nesquehonite is represented as aggregates consisting of chaotically oriented prismatic crystals or kidney-shaped formations. Dypingite in the examined samples appears less frequently as rose-shaped aggregates formed from lamellar crystals. It is assumed that the formation of rare carbonates of the Obnazhennaya kimberlite pipe is mainly the result of the weathering of silicates, formation of mineralized solutions, and their subsequent crystallization, including the capture of CO₂ from the air.

Carbonado is a specific variety of diamonds, typical representatives of which are distributed in the diamond placers of Central Africa, Brazil, and Venezuela. Carbonado consists of the microcrystalline aggregates of diamonds, with inclusions of mineral matter. These aggregates appear as fragments that are rounded to varying degrees. Carbonado has been known for a long time, but its primary sources have not been found and its genesis remains unclear. We have substantiated the hypothesis that the most probable precursor of carbonado is shungite. Shungite is a specific form of non-crystalline, non-graphitic, fullerene-like carbon. Shungite rocks, currently known in Karelia (Russia), are natural microdispersed composite materials containing shungite—carbonaceous matter and mineral components of different compositions. The content of carbonaceous matter in shungite rocks is from less than 10% to 98%. The carbon isotopic composition of shungite is light ẟ¹³C from −25‰ to −40‰. The age of shungite rock is more than 2 billion years old, but earlier shungite was probably much more widespread. Known shungite rocks are more than 2 billion years old, but earlier shungite was probably much more widespread. Shungite rocks could recrystallize into diamond rock upon subduction to high pressure and temperature. The diamond rocks could then be exhumed to the Earth’s surface, where they could undergo disruption and reworking with formation of those very fragments that are known as “carbonado”.

New data on the study of residual pressure in mineral inclusions in diamonds from kimberlite pipes and placers of Yakutia obtained using Raman Spectroscopy are presented. Calculated values of residual pressure in olivine and coesite inclusions in kimberlite diamonds according to works of Israeli et al [1] and Sobolev et al [2] indicate that the host crystal crystallized at the depth not less than 165 km, at pressure of 4.8-5.0 GPa and temperature T=1200 °C. Comparative analysis of Raman spectra of olivine inclusions in diamonds from placers of Ebelyakh river on inclusions, contained in diamond and then brought to the surface, showed that olivine inclusions are less stressed. The structural orientation of olivine inclusions in diamonds from placers of Ebelyakh river possibly plays a role in these differences of Raman spectra.

Yakutites (polycrystalline diamonds with lonsdaleite admixture) from the Ebelyakh placer (Yakutia, Russia) have been studied by optical microscopy, Raman spectroscopy, and neutron diffraction in order to reveal their difference from tagamite-hosted diamonds of the Popigai impact crater. The yakutite aggregates are 2.0 mm to 13.0 mm in size and have a shapeless morphology or sometimes preserve hexagonal contours of primary graphite. Raman spectra are characterized by a broadened line in the region of cubic 3C diamond, which is interpreted as the sum of spectra from cubic 3C diamond and three peaks related to Lonsdaleite: 1338 (E1g), 1280 (A1g) and 1224 (E2g). On the surface of yakutites revealed the presence of a silicate glass film. The main elements are iron, silicon from the surrounding silicate matter. Neutron stress diffractometry showed the content of diamond and Lonsdaleite in the sample of yakutite by 50%, two cases of preferential orientation of two phases were recorded: (110) diamond // (110) Lonsdaleite; (111) diamond // (001) Lonsdaleite. Both yakutites and tagamite-hosted diamonds are of impact origin and share similarity in the phase composition consisting of more abundant diamond and subordinate amounts of lonsdaleite. Differences between them depend on the place of their formation. Yakutites were formed in the epicenter of the explosion and were thrown out of the crater at a distance of more than 550 km in radial directions, and from the vertical ejection - they got back to the crater. In tagamites, impact diamonds were formed simultaneously with the rock melting due to the shock wave that came from the epicenter. The presence of a silicate glass film on the surface of yakutites indicates that they were hardened after ejection from the crater. Yakutites represent distinct mineral fraction outside the crater. They are found as placers along with common diamonds and other detritus. Within the crater they are genetically related to suevites – tuffaceous component of the impactites and enter the crater placers due to the physical weathering of suevites. Tagamite diamonds practically do not occur in the crater placers, because tagamite is a very hard rock and in the absence of chemical weathering these diamonds can’t be released. Thus, diamonds from tagamites and yakutites, having a common impact nature, differ in some properties determined by the place of formation and post-impact history.