Diamonds of Ukraine

Diamonds from Ukraine were studied in terms of their separation into their geological and genetic types, distribution and occurrence, the ages of their host rocks, and their nature in Proterozoic and Neogene age sediments. The placer mantle diamonds are variable in morphology, internal structure, carbon isotopes, concentration and degree of aggregation of nitrogen centers and mineral inclusions. Placer diamonds, primarily from Neogene sands, are anomalous in many respects. They are mostly extremely small, polyhedral, and morphologically diverse showing octahedral, rhombic dodecahedral and cubic forms and they have various colors. In addition to the large heterogeneity in nitrogen concentrations (from 20 to 2000 ppm), many diamonds are characterized by a low degree of aggregation of nitrogen centers, which indicates short mantle residence times. Depending on the nitrogen impurity content, the degree of aggregation of nitrogen centers and the possible temperatures of crystallization, several types of diamonds are distinguished in the studied sedimentary placers. According to new isotope-geochemical data, placer diamonds are characterized by a wide range of carbon isotopic composition (from –33 to +3.3 ‰δ13CVPDB). This may indicate isotopic inhomogeneity of diamond carbon, different modes of formation and chemical variability in their source regions. Impact diamonds from meteorite craters and Neogene sedimentary deposits of Ukraine are paramorphoses from graphite crystals with similar morphological, isotopic and structural characteristics. There are seven meteorite craters and several Neogene placers in the Ukrainian Shield containing impact apographitic diamond. In this work impact diamonds from the Bilylivka meteorite crater and from the Samotkan’ Neogene titanium-zirconium placer were studied in detail. The results of a comprehensive study of impact diamond crystals — morphology, microtopography, microstructure, carbon isotope composition, photoluminescence, optical, infrared, and Raman spectroscopy — are presented. The size of the impact diamonds is up to 0.5mm. Impact diamond crystals are mostly two- or three-phase polycrystalline aggregates (diamond, lonsdaleite, graphite). They show external morphological and internal microstructural features of solid-state phase transition of graphite to diamond during impact shock metamorphism – they are paramorphoses on graphite crystals. Microstructural features of the graphite-diamond transition in the studied crystals of impact diamonds are their polysynthetic (111) twinning and the polycrystalline structure of the twins themselves. The carbon isotopic composition of impact diamonds ranges: for Bilylivka diamonds – from –14.80 to –21.84 ‰ δ13C VPDB, with an average value of –17.21 ‰ δ13C and for Samotkan’ diamonds – from –10.35 to –23.06 ‰ δ13C VPDB, with an average value of –17.64 ‰ δ13C. The photo luminescent and spectroscopic features of the studied diamonds indicate the absence of nitrogen defects in crystals that are characteristic for mantle diamond. The location of the source rocks and potential routes how diamond have been incorporated into the Samotkan’ placer are discussed. The goals of future research of Ukrainian diamonds are discussed. An atlas of diamond crystals of different nature is presented. For a wide range of geologists, mineralogists and crystallographers, as well as for specialists in other fields of science and technology, who study diamonds and artificially obtain them.