This work studies and compares the main morphological, structural, and mineralogical features of 350 diamond crystals from the Karpinsky-I and 300 crystals of the Arkhangelskaya kimberlite pipes. The share of crystals of octahedral habit together with individual crystals of transitional forms with sheaf-like and splintery striation is higher in the Arkhangelskaya pipe and makes 15 %. The share of cuboids and tetrahexahedroids is higher in the Karpinsky-I pipe and stands at 14 %. The share of dodecahedroids in the Arkhangelskaya and Karpinsky-I pipes are 60 % and 50 %, respectively. The indicator role of the nitrogen-vacancy N3 center active in absorption and luminescence is shown. Crystals with the N3 absorption system have predominantly octahedral habit or dissolution forms derived from the octahedra. Their thermal history is the most complex. Absorption bands of the lowest-temperature hydrogen-containing defects (3050, 3144, 3154, 3188, 3310 cm −1 , 1388, 1407, 1432, 1456, 1465, 1503, 1551, 1563 cm −1 ), are typical for crystals without N3 system, where in the absorption spectra nitrogen is in the form of low-temperature A and C defects. The above mentioned bands are registered in the spectra of 16 % and 42 % of crystals from the Arkhangelskaya and Karpinsky-I pipes, respectively. The diamond of the studied deposits is unique in the minimum temperature (duration) of natural annealing. Based on a set of features, three populations of crystals were distinguished, differing in growth conditions, post-growth, and thermal histories. The established regularities prove the multi-stage formation of diamond deposits in the north of the East European Platform and significant differences from the diamonds of the Western Cisurals. The results suggest the possibility of the existence of primary deposits dominated by diamonds from one of the identified populations.
There is shown the possibility of recording the visible and infrared absorption spectra in the faceted gems, including those in jewels. Investigation was carried out with the infrared/visible range spectrometer, equipped with a microscope working in the reflection mode. It is demonstrated the possibility to detect signs of treatment, synthetic origin of diamonds of the main shapes without any sample preparation or removing from jewels.
Results of investigation of large diamond samples from main primary and some placer deposits of Yakutia by FTIR is given. Comparison of various characteristics indicates that maximal difference for samples of diamonds from different sources and minimal diversity for different samples from one source have average values of absorption coefficient and maximum positions of B2 absorption band. The revealed parameters are proposed to be used during comparative analysis of diamonds of different kimberlite pipes, determination of the initial source of placer diamonds, forecasting of new sources.
In the following article, we have studied the variations of natural irradiation of diamond crystals. The natural diamonds in some cases show homogeneous green colour, caused by irradiation of the entire crystals volume. Radiation damage effects, produced by the low-radiation doses, are detected by the luminescence of the GR1 system. The high-radiation doses cause bluish hue, turning into a greenish colour, while the maximum level of volume irradiation produces the black crystals. The crystals with homogeneous volumetric black colour distribution were also studied. The major source of radiation in such cases may represent a local stream containing water rich in 222 Rn and its decay products. There is a review of the geological environment in which diamonds could be irradiated due to the decay of the 222 Rn containing in water.
The article presents the results of a study of the internal structure of highly elongated diamond crystals from placers in the Krasnovishersky district of the Urals. Very elongated crystals are found within diamond-bearing placer with unrevealed primary sources. Determining the conditions of such crystals formation can help one to determine the primary deposits type. There are three hypotheses for the formation of the elongated shape of such crystals: 1) crys- tals initially elongated along the <100> (strongly distorted octahedra); 2) individual crystals of columnar aggregates; 3) elongated crystals fragments. To study the internal structure, we selected three most elongated individuals of the 155 crystals samples. The study of the internal structure of selected crystals with the usage of photoluminescent (PL) tomography, cathodoluminescence (CL), and optical microscopy has shown that these samples are fragments of lar- ger single crystals. CL imaging allowed to determine slip lines within the crystal's volume. The recorded PL spectra show the 912, 946, and 986 nm peaks, which are characteristic of crystals with plastic deformation. The revealed fea- tures are indicators of plastic deformation accompanying the destruction of the crystals. The significant dissolution following the destruction of the crystals led to the rounding of the vertices and edges of their fragments. Apparently, most of the very elongated crystals from placers with unknown sources are also highly dissolved isometric crystal fragments. The obtained results have shown that the deformation and dissolution of diamond crystals are related events characteristic of diamonds from hitherto undetected, but highly productive primary deposits.
