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.     

以碳酸盐为碳源生成金刚石的实验研究

本世纪五十年代初,在金属触媒物质的参与下,由石墨得到金刚石的成功,标志着人工合成超硬材料及高温高压技术两方面的巨大突破。三十年来的科学研究和生产实践推动着这一领域不断地向纵深发展,并提出了建立在不同理论基础上的金刚石生成方法,如爆破法、晶种法、气相生长法、常压高温法、薄膜推移法等等。     

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。     

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.     

湖南砂矿金刚石的颜色

研究表明,湖南砂矿金刚石中存在着两类决定金刚石颜色(主要指黄、褐和绿色)的色心。一类是氮原子中心,有孤氮原子和N3中心。另一类是辐射损伤中心,有GR1、637、595、H3、H4和3H中心。文中还讨论了这些色心的地质意义。     

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.     

Physicochemical formation conditions of natural diamond deduced from experimental study of the eclogite-carbonatite-sulfide-diamond system

A diagram of the syngenesis of diamond, silicate, carbonate, and sulfide minerals and melts is compiled based on experimental data on phase relations in the heterogeneous eclogite-carbonate-sulfidediamond system at P = 7 GPa. Evidence is provided that silicate and carbonate minerals are paragenetic, whereas sulfides are xenogenic with respect to diamond. Diamond and paragenetic phases are formed in completely miscible carbonate-silicate growth melts with dissolved elemental carbon. Coherent data of physicochemical experiment and mineralogy of primary inclusions in natural diamonds allows us to prove the mantle-carbonatite theory of diamond origin. The genetic classification of primary inclusions in natural diamonds is based on this theory. The phase diagrams of syngenesis are applicable to interpretation of diamond and syngenetic minerals formation in natural magma sources. They ascertain physicochemical mechanism of natural diamond formation and conditions of entrapment of paragenetic and xenogenic mineral phases by growing diamonds.     

无色-近无色高温高压合成钻石的谱图特征及其鉴别方法

实验室发现大量小颗粒的无色高温高压(HPHT)合成钻石与天然钻石混杂镶嵌在各种饰品中,前人提出荧光和磷光特征是主要的快速区分特征,然而荧光、磷光特征的差异并不能完全将HPHT合成钻石与天然钻石区分开来。本文将常规的宝石学观察分析与多种高精度谱学测试相结合,对五粒不同的无色-近无色HPHT合成钻石样品进行深入研究。结果表明,五粒钻石在紫外可见吸收光谱无270 nm吸收或是只有极弱的270 nm吸收,随着颜色级别的降低,270 nm吸收越明显。红外光谱测试显示,各粒样品中都含有不等量的硼元素。光致发光光谱测试表明,HPHT合成钻石含有与微量N、Ni、Si等相关的晶格缺陷。超短波紫外光源激发下,所有的HPHT合成钻石都有强磷光,在钻石观察仪下可以观测到清晰的八面体和立方体分区特征。显然,不同的合成钻石的特征略有差异,但综合其荧光及磷光特征以及红外、紫外、光致发光光谱特征,可以准确地将无色HPHT合成钻石与对应的天然钻石区分开来。     

Comparison of enigmatic diamonds from the Tolbachik arc volcano (Kamchatka) and Tibetan ophiolites: Assessing the role of contamination by synthetic materials

The enigmatic appearance of cuboctahedral diamonds in ophiolitic and arc volcanic rocks with morphology and infrared characteristics similar to synthetic diamonds that were grown from metal solvent requires a critical reappraisal. We have studied 15 diamond crystals and fragments from Tolbachik volcano lava flows, using Fourier transform infrared spectrometry (FTIR), transmission electron microscopy (TEM), synchrotron X-ray fluorescence (SRXRF) and laser ablation inductively coupled plasma mass-spectrometry (LA-ICP-MS). FTIR spectra of Tolbachik diamonds correspond to typical type Ib patterns of synthetic diamonds. In TEM films prepared using focused ion beam technique, we find Mn-Ni and Mn-Si inclusions in Tolbachik diamonds. SRXRF spectra indicate the presence of Fe-Ni and Fe-Ni-Mn inclusions with Cr, Ti, Cu, and Zn impurities. LA-ICP-MS data show variable but significantly elevated concentrations of Mn, Fe, Ni, and Cu reaching up to 70 ppm. These transition metal concentration levels are comparable with those determined by LA-ICP-MS for similar diamonds from Tibetan ophiolites. Mn-Ni (+Fe) solvent was widely used to produce industrial synthetic diamonds in the former USSR and Russia with very similar proportions of these metals. Hence, it appears highly probable that the cuboctahedral diamonds recovered from Kamchatka arc volcanic rocks represent contamination and are likely derived from drilling tools or other hard instruments. Kinetic data on diamond dissolution in basaltic magma or in fluid phase demonstrate that diamond does not form under the pressures and temperature conditions prevalent within the magmatic system beneath the modern-day Klyuchevskoy group of arc volcanoes. We also considered reference data for inclusions in ophiolitic diamonds and compared them with the composition of solvent used in industrial diamond synthesis in China. The similar inclusion chemistry close to Ni₇₀Mn₂₅Co₅ for ophiolitic and synthetic Chinese diamonds scrutinized here suggests that most diamonds recovered from Tibetan and other ophiolites are not natural but instead have a synthetic origin. In order to mitigate further dubious reports of diamonds from unconventional tectonic settings and source rocks, we propose a set of discrimination criteria to better distinguish natural cuboctahedral diamonds from those produced synthetically in industrial environments and found as contaminants in mantle- and crust-derived rocks.     

Zonal distribution of impurities in diamond

The zonal distribution of impurities in six diamonds (2 clear. 1 green-skinned, 2 green-bodied and 1 coated) was studied by neutron activation followed by dissolution of the diamond into a number of fractions. High surface concentrations of impurities found here and by other workers were attributed to both laboratory and natural contaminants. No unusual element distributions were found in the outer layer of the green-skinned diamond, the green skin probably being caused by natural radiation damage. The green-bodied diamonds had very different compositions from each other and from the other diamonds and it is suggested that such stones owe their colour to a high general level of impurities. All the diamonds, including the clear core of the coated diamond, contained impurities thought to be submicroscopic inclusions, either silicates, carbonates or immiscible sulphides derived from the parental magma. Variations in the composition of these inclusions in one diamond suggest changes in the host magma composition during growth. Sulphides apparently occurred in very small amounts throughout all the diamonds. Variations in the concentration of impurities are probably related to changes in growth rate or environment during diamond formation, and could explain some of the zonal variations in the physical properties of diamonds.     

The behaviour of platelets in natural diamonds and the development of a new mantle thermometer

Platelets are one of the most common defects occurring in natural diamonds but their behaviour has not previously been well understood. Recent technical advances, and a much improved understanding of the correct interpretation of the main infrared (IR) feature associated with platelets (Speich et al. 2017), facilitated a systematic study of platelets in 40 natural diamonds. Three different types of platelet behaviour were identified here. Regular diamonds show linear correlations between both B-centre concentrations and platelet density and also between platelet size and platelet density. Irregular diamonds display reduced platelet density due to platelet breakdown, anomalously large or small platelets and a larger platelet size distribution. These features are indicative of high mantle storage temperatures. Finally, a previously unreported category of subregular diamonds is defined. These diamonds experienced low mantle residence temperatures and show smaller than expected platelets. Combining the systematic variation in platelet density with temperatures of mantle storage, determined by nitrogen aggregation, we can demonstrate that platelet degradation proceeds at a predictable rate. Thus, in platelet-bearing diamonds where N aggregation is complete, an estimate of annealing temperature can now be made for the first time.     

Crystal forms and surface textures of alluvial diamonds from the Western Region of the Central African Republic

The most common crystal forms of the diamonds from the alluvial deposits in the Western Region of the Central African Republic were examined by scanning electron microscope (SEM) in an attempt to determine their geological history. The marks observed are related to two distinct periods in the geological history of the diamonds: the magmatic episode and their hydraulic transport. The effects of significant magmatic corrosion undergone by the diamonds during their ascent from the upper mantle are shown by the predominance of rhombododecahedral forms over octahedral forms and the frequent occurrence on the crystal faces of pyramidal depressions with triangular (111) or square (100) bases, as well as of V-shaped figures (111) or stepped figures (on the faces around the ternary axes). Some impact marks probably occurred during the explosive episode of kimberlite extrusion. Other impact marks, the marks of general wear, and the high proportion of gemstone-quality diamonds indicate the lengthy transport. They thus also indicate that the diamonds have undergone a prolonged geological history after the erosion of the kimberlite. This suggests that the kimberlite are separated from the Carnot Sandstone Formation by a considerable distance. The diamonds were stored in Albian-Maastrichtian rocks before they become concentrated in the Recent alluvium.     

辽宁天然金刚石晶体缺陷的X射线形貌研究

本文利用透射X射线衍射形貌术研究辽宁天然金刚石晶体缺陷的问题。实验结果表明,金刚石晶体中存在有位错、亚结构及包裹体等缺陷。从这些研究中可以找到辽宁天然金刚石成矿时的某些特点     

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.     

高温高压处理钻石的谱学研究

对高温高压处理钻石进行了显微观察及红外光谱、低温紫外－可见－近红外吸收光谱和光致发光谱等谱学研究，认为钻石的去色是由于高温高压过程引起晶格结构的重组，从而得出天然褐色钻石的致色与位错附近的孤氮－空穴（N－V）的眯缺陷有关的结论。同时也提供了高温高压处理钻石的一些谱学特征，如红外光谱中较弱的3107cm^-1峰，紫外－可见吸收光谱中的325nm宽带，光致发光谱中的575nm与637nm峰。     

金刚石分类、组成特征以及我国金刚石研究展望

金刚石由于其独特的物理化学性质,在经济生产与科学研究中均具有重要价值.金刚石形成于地球大于150 km的深度范围内,是人类可以获得的来自地球深部地幔乃至核幔边界的最直接的样品,因此可以为研究地球深部物质组成和物理化学条件提供重要的素材.金刚石由碳元素组成,还含有微量的杂质元素（如氮、硼、氢、氧等）,其中氮和硼元素对于划分金刚石的晶体结构类型发挥着重要的作用.根据金刚石的产出类型,金刚石可以划分为幔源型、超高压变质型、陨石相关型以及蛇绿岩型金刚石.全球约百分之一的幔源型金刚石含有包裹体,对这些包裹体的研究显示,金刚石主要来源于地球150~200 km深度的岩石圈地幔.这些含有包裹体的金刚石中,仅有1%的金刚石来自于地球深部的软流圈、地幔过渡带、下地幔、甚至核幔边界.我国的金刚石产出类型多样,但是,目前仅山东蒙阴、辽宁复县的金伯利岩矿床以及湖南沅水的砂矿具有经济价值.蛇绿岩型金刚石是近年来金刚石研究领域取得的重要进展,该类型金刚石分布在全球多个造山带不同时代、不同构造属性的蛇绿岩地幔橄榄岩和铬铁矿中,被认为是一种新的金刚石的产出类型.相对于其他国家和地区的金刚石的研究,我国的金刚石领域的研究程度相对较低,缺乏对金刚石结构、化学组成以及包裹体组成的系统研究,制约了对我国金刚石成因的认识,限制了我国的金刚石的找矿工作.因此,亟需结合先进的分析手段对我国的金刚石及其围岩做进一步的研究,以期揭示金刚石的形成过程,为金刚石的找矿提供理论基础.      

金刚石中过渡金属的研究现状

为了揭示金刚石的合成机理与过渡金属杂质离子对金刚石物理性质的影响，国内外展开了对合成金刚石及天然金刚石中镍，钴和铁等过渡金属杂质的实验与理论研究，各种吸收与发光光谱法和电子顺磁共振，被用于金刚石中过渡金属离子赋存状态的研究中，结果表明镍、钴离子可以间隙形式或替代方式进入晶格。     

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。     

A Diamondiferous Lamprophyre Dike,Gibson Lake Area,Northwest Territories

The Akluilak dike is a narrow lamprophyre intrusion of ultrapotassic composition that has yielded a large content of diamonds; it is the first multidiamond occurrence noted from the central Churchill Province. Xenocrysts of apatite containing monazite have been dated at 1832 ± 28 Ma, thus confirming the correlation with Christopher Island Formation volcanic and intrusive rocks. Only 1 or 2 diamonds per 1000 are greater than 0.5 mm, and the majority are less than 0.075 mm. They occur primarily as octahedra and tetrahexahedroids, but cubes, macles, aggregates, and fragments also are present. Their occurrence points to the presence of a “mantleroot-friendly” lithosphere, and confirms the “highly diamond prospective” nature of the area suggested by previous studies.     

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.