The ordered creation of paramagnetic defects at plastic deformation of natural diamonds

The EPR-study showed that natural purple diamonds from kimberlites of Eastern Siberia (Russia) contain well known P1, P2 (in some samples), W7, and N2 centers. The EPR spectra of these centers were typical of plastically deformed diamond single crystals. Besides, several intense additional spectra of di-nitrogen centers were observed in purple diamonds. The angular dependence analysis of these spectra showed that they can be attributed to known M2 centers. Comparison of principal axis directions observed for sites of the M2 center in purple diamond crystals with theoretically predicted directions in the twin crystal revealed that these centers are allocated exclusively to the twinned lamellae. Unusual phenomenon of the ordered distribution of paramagnetic centers in natural purple diamonds confirmed that the plastic deformation in natural diamonds can be induced not only by the slip of dislocations but also by the mechanical twinning.     

Causes of variations in morphology and impurities of diamonds from the Udachnaya Pipe eclogite

A unique xenolith of eclogite, 23×17×11 cm in size and 8 kg in weight, was found in the Udachnaya kimberlite pipe. One hundred twenty-four diamond crystals recovered from it were analyzed by a number of methods. The diamonds differ in morphology, internal structure, color, size, and composition of defects and impurities. The xenolith contains diamonds of octahedral and cubooctahedral habits. In cathodoluminescence, the octahedral crystals have a brightly glowing core with octahedral zones of growth and a weakly glowing rim. In the cores of these crystals the N impurity is mostly present in the B1 form (30 to 60%). At the same time, N in the rim is chiefly in the A form. The cubooctahedral crystals show a weak luminescence. The content of nitrogen and degree of its aggregation are close to those in the rim of octahedral crystals. The diversity of morphology and impurity composition of diamonds from the xenolith can be explained by their formation in two stages. At the first stage, the diamonds formed which became the cores of octahedra. After a long-time interruption, at the second stage of diamond formation crystals of cubooctahedral habit appeared and the octahedral crystals were overgrown. Wide variations in nitrogen contents in the xenolith crystals allowed their use to estimate the kinetics of aggregated nitrogen. The data obtained show that the aggregation of A centers into B1 centers in the diamonds is described by a kinetic reaction of an order of 1.5.     

Structural defects in natural plastically deformed diamonds: Evidence from EPR spectroscopy

Structural defects formed as a result of plastic deformation in natural diamond crystals have been studied by EPR spectroscopy. The spectra of brown, pink-brown, black-brown, pink-purple, and gray plastically deformed diamonds of type Ia from deposits in Yakutia and the Urals were recorded. The results of EPR spectroscopy allowed us to identify various deformation centers in the structure of natural diamonds and to show that nitrogen centers were transformed under epigenetic mechanical loading. Abundant A centers, consisting of two isomorphic nitrogen atoms located in neighboring structural sites, were destroyed as a result of this process to form a series of N1, N4, W7, M2, and M3 nitrogen centers. Such centers are characterized by an anisotropic spatial distribution and a positive charge, related to the mechanism of their formation. In addition, N2 centers (probably, deformation-produced dislocations decorated by nitrogen) were formed in all plastically deformed diamonds and W10 and W35 centers (the models have not been finally ascertained) were formed in some of them. It has been established that diamonds with various types of deformation-induced color contain characteristic associations of these deformation centers. The diversity of associations of deformation centers indicates appreciable variations in conditions of disintegration of deep-seated rocks, transfer of diamonds to the Earth’s surface, and formation of kimberlitic deposits. Depending on the conditions of mechanical loading, the diamond crystals were plastically deformed by either dislocation gliding or mechanical twinning. Characteristic features of plastic deformation by dislocation gliding are the substantial prevalence of the N2 centers over other deformation centers and the occurrence of the high-spin W10 and W35 centers. The attributes of less frequent plastic deformation by mechanical twinning are unusual localization of the M2 centers and, in some cases, the N1 centers in microtwinned lamellae. Numerous data on models of deformation centers in natural diamonds, including the M2 and M3 centers, which were observed in the studied collection for the first time, are discussed.     

New data of typomorphic features of diamonds from placers in North Timan

The morphological and spectral-optical properties of diamond crystals from placers in North Timan rivers have been studied with IR-spectroscopy and cathode luminescence methods. As a result, correlation between external characteristics of diamonds (size and degree of mechanical damage) and number of optically active centers has been revealed. The habit and the type of distribution of structural defects in diamond crystals studied are comparable with those in diamonds from the Archangelsk Region and North Timan’s placers. Based on the obtained data, origin issues and possible primary sources of diamonds from North Timan’s placers are discussed.     

Luminescence in diamonds of the Sao Luiz placer (Brazil)

Plates made of diamonds from the Sao Luiz province (Brazil) were investigated by confocal scanning luminescence microscopy. The samples have many macroinhomogeneities (cracks and inclusions), but there is a quasi-uniform distribution of luminescence centers in the bulk. At all investigated points of the crystals, the same group of centers was observed: N3, H4, 575, and a red band with a maximum at 690-700 nm. The visible nonuniformities in the distribution of luminescence over the area of the plates are determined by relatively small fluctuations in the ratio of the intensities of individual bands in the spectra. Nitrogen centers of different degrees of aggregation (H4, N3, and 575 nm, with four, three, and one nitrogen atom, respectively) coexist in these crystals. In the same zones of the samples, the distribution of blue luminescence (N3 centers) is diffuse (uniform), but the distribution of yellow-green luminescence is characterized by layering on (111). This might be a consequence of the tangential growth of octahedron faces or a result of plastic deformation of the crystals and dislocations along (111).     

HPHT合成钻石在首饰中的鉴别特征

国家黄金钻石制品质量监督检验中心收到待检的百余件群镶钻石首饰中发现混有大量HPHT合成黄色钻石.采用宝石显微镜、红外光谱仪、X射线荧光光谱仪、紫外可见光分光光谱仪、紫外荧光灯、DiamondView^TM等对HPHT合成钻石样品做了详细地测试与分析.结果表明,这些HPHT合成钻石样品具有较为统一的黄色,放大检查可见合成钻石内部含有大量棒状、柱状、细小微粒状的铁镍合金包裹体,且几乎都有磁性,有些磁性甚至较强;样品的红外反射光谱非常特征,均具有明显的1 131 cm^-1处的吸收峰,为Ⅰb型钻石,而Ⅰb型钻石在天然钻石中极少见到;X射线荧光光谱测试显示有强烈的铁峰和镍峰,且在短波紫外线下多数具有绿黄色荧光.HPHT合成钻石在DiamondView^TM下具有不同程度的黄绿色荧光,部分具有黑十字现象.     

Origin of disequilibrium diamond crystals from Karpinsky-1 kimberlite pipe using data from cathode luminescence and infra red spectroscopy

The internal structures of 78 diamond crystals from the Karpinsky-1 pipe in the Arkhangelsk Province and the distributions of structural impurities in them were examined by the methods of cathode luminescence and IR spectroscopy. Three generations of diamonds were found in the pipe. Diamonds of the first and second generations presumably originated in an ultramafic and eclogite mantle medium. Diamonds of the third generation, which are very common in the pipe, show a fibrous internal structure and anomalously high concentrations of nitrogen and hydrogen; they originated under disequilibrium conditions. The third-generation diamonds differ by the set of their typomorphic features from diamonds of kimberlite origin and show some similarity with diamonds from metamorphic rocks. We hypothesize that the third-generation diamonds from Katpinsky-1 pipe could originate in a proto-kimberlitic melt.     

辐射处理金刚石的谱学研究及其意义

利用傅立叶显微红外光谱、紫外-可见-近红外吸收光谱、低温光致发光谱、拉曼光谱等4种谱学方法,对10颗辐照改色（R1-R10）的彩色天然金刚石进行了研究。利用可见吸收光谱和低温光致发光谱研究了金刚石石中的点缺陷产生系列的色心峰,指出在可见吸收光谱中除了有N3心吸收峰外,还可见595和637色心峰;在低温光致发光谱中发现有色心组合峰575,595和637等的出现,此组合峰与近红外区4929cm^-1处的H1b和5156cm^-1处的H1C色心峰共同存时,不仅是辐照处理绿色金刚石的鉴定证据,也是辐照处理各种彩色金刚石的重要的标志之一。本研究为辐射处理金刚石的鉴别和工艺流程提供了新的谱学依据和思路。     

Zoning of diamonds from the Mir kimberlite pipe: Results of Fourier-transformed infrared spectroscopy

Plates prepared of diamonds from the Mir kimberlite pipe were examined with FTIR spectroscopy. It is shown that B1 defects were formed by annealing during crystal growth, whereas B2 centers arose after growth cessation. The development of B2 centers in a natural diamond is the secondary process with respect to the aggregation of the nitrogen admixture. The kinetics of this process is related to the breakdown of an oversaturated solid solution. The results obtained make it possible to estimate the temperature and duration of natural diamond growth.     

Sites of the N1 nitrogen paramagnetic centers in natural diamond crystals: Dissymmetrization of the structure as a result of plastic deformation

Using the method of EPR spectroscopy, it is shown that the N1 nitrogen centers (N–C–N⁺) are unevenly distributed over possible sites in natural brown crystals of plastically deformed diamonds. The influence of deformational dissymmetrization of the structure on the anisotropy of some physical properties of natural diamonds is discussed.     

The transformation features of impurity defects in natural diamonds of various habits under high <Emphasis Type="Italic">P</Emphasis>–<Emphasis Type="Italic">T</Emphasis> conditions

The results of the investigations of the transformation of impurity defects in natural diamonds of various habits at the stage of high-temperature annealing at P = 6 GPa and T = 2200°C are presented. The studies conducted allowed us to ascertain that the transformations of Aand B-defects in diamonds of octahedral and cubic habits follow general regularities. This fact shows that most of the diamonds of cubic habit with low degree of aggregation of nitrogen centers were not really annealed over a long-term interval. Unlike octahedral diamonds, those of cubic habit are characterized by a pronounced increase in the peak of H-containing defects (3107 cm^–1) after annealing.     

The secondary origin of diamonds: multi-modal radiation tomography of diamondiferous mantle eclogites

Three-dimensional neutron and X-ray tomography reveals the textural and spatial relationship of diamonds and associated minerals in situ, in a unique suite of 17 diamondiferous eclogites. We emphasize the reporting of X-ray imaging on mantle xenoliths, which in combination with neutron imaging enables the clear identification of diamonds and interstitial metasomatic secondary minerals. In particular, neutrons are highly sensitive to hydrogen (H), allowing for the identification of OH- and H₂O-bearing metasomatic minerals. The identification of metasomatic minerals allows for the delineation of distinct metasomatic pathways through the eclogite xenoliths. Diamonds are readily identified as the darkest greyscales due to their low attenuation, and are typically surrounded by secondary minerals, never in contact with primary minerals, and always confined within metasomatic pathways. The ubiquitous occurrence of diamonds in association with pathways suggests a potential genetic link. Both octahedral and dodecahedral diamonds are observed within individual xenoliths, suggesting multiple heterogeneous growth and dissolution processes at small scales. The distinct age dichotomy between eclogite xenoliths and metasomatic mineral assemblages implies that the observed textural relationship of diamonds and late-stage metasomatic pathways for this suite of 17 eclogites casts doubt on the theory that eclogitic diamonds formed billions of years ago. Diamonds are interpreted to have formed from multiple growth episodes, with the last of these episodes represented by the metasomatic assemblages observed in this study. This further indicates that eclogitic diamond inclusions may span large time scales from ancient ages (>2 Ga) all the way to the last growth event, perhaps even close to the time of kimberlite emplacement (~360 Ma), which has significant implications for age-dating of diamonds and the study of diamonds as a whole.     

中国3个商业性钻石产地天然钻石的Diamond ViewTM图像及其意义

对采自我国3个商业性产地山东蒙阴、辽宁瓦房店、湖南常德地区的236片/颗天然钻石样品进行了系统的DiamondViewTM(DV)荧光图像分析,结合CL照相和FTIR的定量计算,探讨了钻石样品DV图像发光结构模式和荧光颜色方面的差异性及其原因。结果表明,3个产地钻石的DV图像和CL图像显示的钻石生长结构基本一致;钻石的发光结构模式与钻石内部氮、氢元素的种类和浓度分布趋势没有明显的一致性,DV图像模式并不完全受钻石类型控制,但DV图像的色调与钻石存在的杂质元素及晶体缺陷有关。钻石的DV图像特征受钻石的生长环境、结晶条件、后期熔蚀、辐照损伤等因素综合制约。从统计学的角度看,3个产地钻石的DV发光模式和荧光颜色有一定的差异,这种差异可以作为区分不同产地来源的钻石的宏观的统计学特征。DiamondViewTM技术在揭示天然钻石生长结构方面和CL发光照相技术效果近似,但更加便利。     

First diamonds from placers in Primorie

The paper reports the results obtained by the detailed studying of carbonado (the first find in a gold placer in Primorie) and a collection of diamonds that was confiscated in 1937 from a poaching small digger and was kept safe at the Nezametnyi mine (near the village of Vostretsovo), which had developed this placer deposit. In the concentrate from the placer, carbonado is associated with green corundum, various ilmenite, zircon titanian amphiboles and pyroxenes, rutile, anatase, and fragments of subvolcanic biotite picrites. All of these minerals, native aluminum, and tin occur as inclusions in the diamonds. The carbonado from Primorie was determined to be practically identical to this mineral from Brazil, has a porous structure, is characterized by orange luminescence, contains inclusions of Y, Ce, La, Ba, and Sr phosphates, and has an isotopically light composition of its carbon (¹³C from ?25 to ?32‰). Pores of the carbonado aggregates contain clusters of diamond crystals. The collection of diamonds from an unknown source included six gem-quality transparent crystals, one rounded ballas, two cuboctahedral crystals (one of greenish and the other of silver-gray color, both with outer coats), and one black carbonado grain. The data obtained on the mineralogy of the diamonds have demonstrated that they are completely identical to this mineral from kimberlites and lamproites but bear traces of intense dissolution, fragmentation, multiple recrystallization, and graphitization at defects, which are the most widespread in the ballas. One of the crystals was determined to contain inclusions: aggregates of potassic omphacite (0.50 wt % K₂O) and corundum. Ilmenite (containing up to 8 wt % MgO), titanaugite, kaersutite (4 wt % TiO₂, 0.8 wt % K₂O), and churchite (aqueous phosphate) were obtained from the core of the ballas. The titanaugite, kaersutite, and ilmenite were proven to be compositionally analogous to these minerals from picrites occurring near the placer. The carbon isotopic composition δ¹³C of the cores of the single diamond crystals varies from ?6 to ?11‰. The margins of the grains were proved to be enriched in the light carbon isotope (δ¹³C from ?19 to ?21‰). The gem-quality transparent diamond crystals are characterized by blue luminescence, and the color of luminescence in the carbonado varies from orange red in the bulk of the aggregate to yellowish green in its core. The aforementioned transformations of diamonds were likely caused by their transportation in pipes of micaceous picrites of the Jurassic meymechite complex. The carbonado are thought to correspond to the final stage of the metastable recrystallization (in pores, within the temperature range of the rutile-anatase transition) of the original isotopically heavy diamonds under the effect of various oxidizers (H₂O, CO₂, F, and others) and in the presence of catalytically acting REE, Ti, and P. The primary diamond source (kimberlite or lamproite) can be older and more distant from the study area. The complete geological analogy between the study area in Primorie, Kalimantan Island in Indonesia, and West Australia (where no sources of the placers are known) led us to consider the territory of Primorie as promising for exploration for diamondiferous placers.     

CVD合成钻石的层状生长结构和紫外荧光特征

最近NGTC实验室检测出多批次CVD合成钻石,这些CVD合成钻石均具有明显的鉴定特征,使用钻石观测仪（DiamondViewTM）观察可见蓝色、橙红色荧光和蓝色磷光以及细密层状生长纹理,光致发光光谱中可见737 nm处的特征发光线.这些特征均与其生长结构及生长过程中进入钻石晶体中的杂质有关.笔者以最近检测过程中发现的一颗CVD合成钻石为例,使用高倍率显微技术对其层状结构的微细特征及其在钻石观测仪下的荧光特征的关系进行了详细观察和对比.结果显示,此样品与之前检测到的CVD合成钻石略有差异.此次检测到的样品在钻石观测仪（DiamondViewTM）下观察具有较宽的层状生长分区,层与层之间的分界线十分明显且在高倍显微镜下也可见到细微的生长特征.通过对样品特征的分析,了解了晶体生长过程中多阶段生长条件的变化,更直观的展现了CVD合成钻石的生长过程.     

Carbon isotopic composition of diamonds in Ukraine and their probable polygenetic nature

The paper presents newly obtained data on the mineralogical and geochemical characteristics of Ukrainian endogenic and supergenic diamonds, including pioneering data on the carbon isotopic composition of individual diamond crystals. The endogenic diamonds occur as euhedral microcrystals (their morphology varies from octahedral to rhombododecahedral and cubic) with broadly varying concentrations of the structural nitrogen admixture and with mostly low aggregation of nitrogen centers. According to their carbon isotopic composition, Ukrainian diamonds range from kimberlitic–lamproitic to metamorphic and even carbonado-like, i.e., are polygenetic. Our data confirm the earlier conclusion that the supergenic diamonds are of impact genesis.     

Regional patterns in the paragenesis and age of inclusions in diamond, diamond composition, and the lithospheric seismic structure of Southern Africa

The Archean lithospheric mantle beneath the Kaapvaal–Zimbabwe craton of Southern Africa shows ±1% variations in seismic P-wave velocity at depths within the diamond stability field (150–250 km) that correlate regionally with differences in the composition of diamonds and their syngenetic inclusions. Seismically slower mantle trends from the mantle below Swaziland to that below southeastern Botswana, roughly following the surface outcrop pattern of the Bushveld-Molopo Farms Complex. Seismically slower mantle also is evident under the southwestern side of the Zimbabwe craton below crust metamorphosed around 2 Ga. Individual eclogitic sulfide inclusions in diamonds from the Kimberley area kimberlites, Koffiefontein, Orapa, and Jwaneng have Re–Os isotopic ages that range from circa 2.9 Ga to the Proterozoic and show little correspondence with these lithospheric variations. However, silicate inclusions in diamonds and their host diamond compositions for the above kimberlites, Finsch, Jagersfontein, Roberts Victor, Premier, Venetia, and Letlhakane do show some regional relationship to the seismic velocity of the lithosphere. Mantle lithosphere with slower P-wave velocity correlates with a greater proportion of eclogitic versus peridotitic silicate inclusions in diamond, a greater incidence of younger Sm–Nd ages of silicate inclusions, a greater proportion of diamonds with lighter C isotopic composition, and a lower percentage of low-N diamonds whereas the converse is true for diamonds from higher velocity mantle. The oldest formation ages of diamonds indicate that the mantle keels which became continental nuclei were created by middle Archean (3.2–3.3 Ga) mantle depletion events with high degrees of melting and early harzburgite formation. The predominance of sulfide inclusions that are eclogitic in the 2.9 Ga age population links late Archean (2.9 Ga) subduction-accretion events involving an oceanic lithosphere component to craton stabilization. These events resulted in a widely distributed younger Archean generation of eclogitic diamonds in the lithospheric mantle. Subsequent Proterozoic tectonic and magmatic events altered the composition of the continental lithosphere and added new lherzolitic and eclogitic diamonds to the already extensive Archean diamond suite.     

Aspects of diamond mineralisation and distribution at the Helam Mine, South Africa

The diamonds from the Swartruggens dyke swarm are mainly tetrahexahedra, with subsidiary octahedral and cuboid crystals. They are predominantly colourless, with subordinate yellows, browns, and greens. The existence of discrete cores and oscillatory growth structures within the diamonds, together with the recognition of harzburgite, lherzolite, at least two eclogitic and a websteritic diamond paragenesis, variable nitrogen contents, and both Type IaAB and Type Ib–IaA diamonds provides evidence for episodic diamond growth in at least six different environments. The predominance of plastic deformation in the diamonds, the state of nitrogen aggregation, and the suite of inclusion minerals recovered are all consistent with a xenocrystic origin for the diamonds, with the Type Ib–IaA diamonds being much younger than the rest. Mantle storage at a time-averaged temperature of ±1100 °C is inferred for the Type IaAB diamonds. The distribution of mantle xenocrysts of garnet and chromite within the high-grade Main kimberlite dyke compared to the low-grade Changehouse kimberlite dyke strongly suggests that the difference in diamond content is due to an increased eclogitic component of diamonds in the Main kimberlite dyke.     

Nature of diamonds in Yakutian eclogites: views from eclogite tomography and mineral inclusions in diamonds

We have performed dissections of two diamondiferous eclogites (UX-1 and U33/1) from the Udachnaya kimberlite, Yakutia in order to understand the nature of diamond formation and the relationship between the diamonds, their mineral inclusions, and host eclogite minerals. Diamonds were carefully recovered from each xenolith, based upon high-resolution X-ray tomography images and three-dimensional models. The nature and physical properties of minerals, in direct contact with diamonds, were investigated at the time of diamond extraction. Polished sections of the eclogites were made, containing the mould areas of the diamonds, to further investigate the chemical compositions of the host minerals and the phases that were in contact with diamonds. Major- and minor-element compositions of silicate and sulfide mineral inclusions in diamonds show variations among each other, and from those in the host eclogites. Oxygen isotope compositions of one garnet and five clinopyroxene inclusions in diamonds from another Udachnaya eclogite (U51) span the entire range recorded for eclogite xenoliths from Udachnaya. In addition, the reported compositions of almost all clinopyroxene inclusions in U51 diamonds exhibit positive Eu anomaly. This feature, together with the oxygen isotopic characteristics, is consistent with the well-established hypothesis of subduction origin for Udachnaya eclogite xenoliths. It is intuitive to expect that all eclogite xenoliths in a particular kimberlite should have common heritage, at least with respect to their included diamonds. However, the variation in the composition of multiple inclusions within diamonds, and among diamonds, from the same eclogite indicates the involvement of complex processes in diamond genesis, at least in the eclogite xenoliths from Yakutia that we have studied.     

Laser-induced time-resolved luminescence of tugtupite,sodalite and hackmanite

We have interpreted a number of luminescence centers in natural tugtupite Na₈Al₂Be₂Si₈O₂₄Cl₂, sodalite Na₈Al₆Si₆O₂₄C₂ and hackmanite Na₈Al₆Si₆O₂₄(Cl₂,S) by use of laser-induced time-resolved luminescence spectroscopy. The main new results are the following: Fe³⁺, Mn²⁺, Eu²⁺, Ce³⁺, mercury type (potentially Pb²⁺, Tl⁺, Sn²⁺ and/or Sb³⁺), radiation induced luminescence centers; several types of S₂ ⁻ centers. Spectral shift connected with the presence of luminescence centers, which are detected together with S₂ ⁻ centers and impossible to resolve with continuous wave luminescence spectroscopy, is the possible reason for spectral diversity of S₂ ⁻ luminescence centers presented in different publications.