天然金刚石的定向红外光谱研究

本文对天然金刚石在垂直于（100）、（110）和（111）三个方向上定向红外光谱进行了定量比较分析，指出C－H键和C－C键在以上三个方向上的浓度不相同，引起C－C键和C－C键在不同方向上的浓度差异是由于氢具有优先取代垂直于（111）方向上C－C键中碳原子的倾向。     

金刚石中水的研究

根据红外光谱定量分析的原理，利用吸收峰位之间的相关性，判别出金刚石中结构水(-OH)的伸缩振动频率为3760cm^-1；水分子的反对称伸缩与对称伸缩振动频率分别为3630cm^-1和3200cm^-1。在分别垂直于金刚石(100)、(110)及(111)方向上的定向显微红外光谱研究表明：-OH、H2O及C-C键在不同方向上所测得的浓度是不相同的；样品本身存在晶格畸变；-OH和H2O共有的OH基团在金刚石中的取向并不相同；-OH和H2O并没有进入金刚石的晶格，更多的可能是存在于金刚石的空隙中。     

金刚石中分子氢的赋存状态研究

金刚石中分子氢的定向红外光谱研究表明在垂直于(100),(110)和(111)三个方向上所测得分子氢的浓度是不相同的,且不同样品中的变化趋势也不同,即分子氢在金刚石中的定向性不明显;MNDO法计算结果显示分子氢在金刚石中的稳定程度大小关系依次为沿〈111〉定向的键心与反键心组合(a.b+b.c)〉六角体空隙(H)〉四面体空隙(T1)〉菱形中心(C1＝C2)〉四面体空隙(T2).     

金刚石中的成键氢

金刚石中杂质相的研究一直倍受关注,但大多集中在B、N两种杂质的研究上,而对于氢在其中的赋存状态研究则刚刚开始。从振动谱学（IR、Raman）的角度对氢在金刚石中的一种赋存状态--成键氢进行的研究表明,成键氢在金刚石中可以以碳氢键、H2及 O-H键的形式存在。     

硬玉微区显微红外光谱分析

缅甸硬玉的微区显微红外光谱中出现的OH、C—H、C=O基团的定量比较分析表明，在不同颜色硬玉中其浓度差异明显；说明硬玉的颜色与物化环境的局部变异密切相关，是在一个复杂的有机与无机的天然环境中形成；在合成不同颜色硬玉时，需与适当的物化环境相匹配，尤其是绿色硬玉，才有利于硬玉的生长。     

丙烯酸酯类聚合物充填绿松石的红外光谱特征

丙烯酸酯类聚合物是绿松石充填处理常用的高分子聚合物。利用傅里叶变换红外光谱仪测试并研究各种用于绿松石充填处理的丙烯酸酯类聚合物的红外光谱以及经其充填处理后绿松石的红外光谱,寻找并总结出经过丙烯酸酯类聚合物充填处理后绿松石的红外光谱鉴定特征。研究发现,可用红外光谱中νs(CH2、CH3)吸收谱带与ν(C=O)吸收谱带的相对强弱来鉴别丙烯酸酯类聚合物充填处理的绿松石。     

阴极发光和红外光谱技术在金刚石研究中的应用

总结了阴极发光（ＣＬ）及傅立叶变换红外光谱（ＦＴＩＲ）技术在金刚石研究中的应用。ＣＬ图像可以揭示金刚石的内部结构、生长机制、生长阶段及过程,提供塑性变形及是否含有ＣＯ２的信息,验证和解释微区ＦＴＩＲ分析、稳定同位素及地质年代研究的结果,为天然金刚石和合成金刚石的区分提供关键证据。合成金刚石的实验研究表明,氮的不同聚集态丰度值是聚集温度ＴＮＡ、金刚石存留时间ｔＭＲ及氮丰度值的函数,利用地质信息和ＦＴ     

傅立叶红外光谱技术在翡翠研究中的应用

基于透射光谱的差异，用傅立叶红外光谱研究翡翠的矿物组成；分析硬玉、霓石、霓辉石和透辉石等主要矿物，以天然翡翠的特征红外光谱为依据，鉴别市售翡翠的真伪和类别（Ａ、Ｂ货）；利用红外显微镜作微区透射光谱，鉴别通常难以鉴别的有裂缝及裂缝填充物的翡翠（Ｂ货），提出了准确的无损鉴别翡翠的方法。     

挪威西部片麻岩区高级变质岩中的微粒金刚石

从挪威西部片麻岩区的高级片麻岩中回收了３颗粒金刚石。通过拉曼和红外光谱鉴定并测定这３颗微粒金刚石的特征，发现它们的结构中有Ｈ和Ｎ的替代杂质。通过对含金刚石中的石榴石和石英矿物中的原生流体包裹体的研究，证明变质挥发分流体发生了演化，即从变质高峰期间还原的Ｎ２－ＣＯ２成分演化到退变质作用期间含Ｎ２－ＣＨ４±Ｈ２Ｏ成分。     

西藏罗布莎橄榄岩与中国大陆科学钻探主孔(CCSD-MH)榴辉岩中金刚石的红外特征初探

大别苏鲁超高压变质带上的大陆科学钻探主孔(CCSD-MH)中榴辉岩中的金刚石形成于大陆深俯冲作用过程,西藏雅鲁藏布江缝合带罗布莎蛇绿岩铬铁矿中的金刚石来自深部地幔,两者的形成背景和机制可能不同.本文对两地的金刚石样品开展了傅立叶变换红外光谱(FT-IR)定性分析.结果表明,西藏罗布莎金刚石样品为ⅠaA型;而CCSD-MH金刚石为ⅠaAB型,既表明其杂质氮的聚集形式和演化路径上存在着差异.红外光谱特征不仅仅表明两者属天然金刚石常见类型,并且超高压变质带中的金刚石形成时间可能更久远.     

湖南金刚石内部不均一性特征研究

将湖南金刚石加工成片，利用宝石显微镜，偏光镜，阴极发光（CL）仪和傅里叶红外光谱（FTIR）仪对其内部显微特征进行了研究，发现金刚石的颜色深浅不一，内外颜色差异明显，呈带状，斑状分布；金刚石由生长中心至边缘，氮含量也有较大变化，中心与边缘最大相差约50倍，氮的富集类型由中心向边缘表现出B中心所占的比例越来越小，金刚石的类型也相应从I型→II型或I－aAB型→-I-aA型等，这些不均一性特征，反映金刚石在生长过程中环境条件发生了变化，以及生长期后可能受到了改造。     

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.     

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.     

Syngenetic inclusions of yimengite in diamond from Sese kimberlite (Zimbabwe) — evidence for metasomatic conditions of growth

Syngenetic inclusions of yimengite K (Cr, Ti, Mg, Fe, Al)₁₂O₁₉, a potassium member of the magnetoplumbite mineral group, have been recorded in an octahedral macrodiamond from the Sese kimberlite (50 km south of Masvingo, Zimbabwe). One yimengite inclusion carries lamellae of chromite suggesting peridotitic diamond paragenesis. The diamond and inclusions were studied in situ in a plate polished parallel to (011). Cathodoluminescence (CL) imaging has shown blue colour and octahedral zonation of the diamond, lack of cracks and the location of five yimengites in different growth zones. Nitrogen (N) contents (at. ppm) in the diamond determined by Fourier transform infrared spectroscopy (FTIR) steadily decrease from 576 (core) to 146 (rim). N aggregation (%1aB) is correspondingly 40% in the core and 30% in the rim. Hydrogen (H) content is high in the core, moderate in the intermediate and very high in the rim zones. Four yimengites were dated using the laser ⁴⁰Ar/³⁹Ar method. Three inclusions yielded total gas ages that agree with, or are younger than, or within error of, the Sese kimberlite eruption age (538±11 Ma) but may be compromised by gas loss. One inclusion, with the highest tapped interface gas yield, gave a total gas age of 892±21 Ma that is a likely minimum yimengite age. Time–T °C constraints from N aggregation systematics give a range of possible ages from kimberlite eruption date back to Archean and do not resolve the variable results of the ⁴⁰Ar/³⁹Ar dating. Compared with the published chemistry of yimengite from kimberlites, inclusions from the Sese diamond contain higher Al, Mg, and Sr and have lower concentration of Fe³⁺. The chondrite-normalised REE pattern of the yimengite shows enrichment in LREE and depletion in HREE, but LREE/HREE fractionations are lower than for lindsleyite–mathiasite series mantle titanates and rather similar to the REE concentrations in kimberlite and lamproite rocks. It is suggested that Sese yimengite formed in the lithospheric mantle from metasomatism of chrome spinel by a fluid rich in Ti, K, Ba and LREE.     

The first finding of graphite inclusion in diamond from mantle rocks: The result of the study of eclogite xenolith from Udachnaya pipe (Siberian craton)

A xenolith of eclogite from the kimberlite pipe Udachnaya–East, Yakutia Grt+Cpx+Ky + S + Coe/Qtz + Dia + Gr has been studied. Graphite inclusions in diamond have been studied in detail by Confocal Raman (CR) mapping. The graphite inclusion in diamond has a highly ordered structure and is characterized by a substantial shift in the band (about 1580 cm^–1) by 7 cm^–1, indicating a significant residual strain in the inclusion. According to the results of FTIR spectroscopic studies of diamond crystals, a high degree of nitrogen aggregation has been detected: it is present mainly in form A, which means an “ancient” age of the diamonds. In the xenolith studied, the diamond formation occurred about 1 Byr, long before their transport by the kimberlite melt, and the conditions of the final equilibrium were temperatures of 1020 ± 40°C at 4.7 GPa. Thus, these graphite inclusions found in a diamond are the first evidence of crystallization of metastable graphite in a diamond stability field. They were formed in rocks of the upper mantle significantly below (≥20 km) the graphite-diamond equilibrium line.     

Formation of mosaic diamonds from the Zarnitsa kimberlite

Mosaic diamonds from the Zarnitsa kimberlite (Daldyn field, Yakutian diamondiferous province) are morphologicaly and structurally similar to dark gray mosaic diamonds of varieties V and VII found frequently in placers of the northeastern Siberian craton. However, although being similar in microstructure, the two groups of diamonds differ in formation mechanism: splitting of crystals in the case of placer diamonds (V and VII) and growth by geometric selection in the Zarnitsa kimberlite diamonds. Selective growth on originally polycrystalline substrates in the latter has produced radial micro structures with grains coarsening rimward from distinctly polycrystalline cores. Besides the formation mechanisms, diamonds of the two groups differ in origin of mineral inclusions, distribution of defects and nitrogen impurity, and carbon isotope composition. Unlike the placer diamonds of varieties V and VII, the analyzed crystals from the Zarnitsa kimberlite enclose peridotitic minerals (olivines and subcalcic Cr-bearing pyropes) and have total nitrogen contents common to natural kimberlitic diamonds (0 to 1761 ppm) and typical mantle carbon isotope compositions (-1.9 to -6.2%c 5¹³C; -4.2%c on average). The distribution of defect centers in the Zarnitsa diamond samples fits the annealing model implying that nitrogen aggregation decreases from core to rim.     

The relationship between the distribution of nitrogen impurity centres in diamond crystals and their internal structure and mechanism of growth

Fifty diamond crystals of different morphological types (octahedra, dodecahedroids, cubes and single tetrahexahedroid) with differing internal structures were examined using methods of cathodoluminescence (CL), anomalous birefringence and local infrared (IR) analysis. The main objective of the study was to examine the regularities of nitrogen impurity distribution in diamond with differing internal structures. Almost all the analyzed octahedra, as well as dodecahedroids with zonal structures and the blocky dodecahedroids, are characterized either by nearly isothermic growth conditions or by a decrease in formation temperature during the crystallization process. In contrast to zoned octahedra and dodecahedroids, dodecahedroids with zonal–sectorial and sectorial internal structures show a notably different distribution of nitrogen defects, with N_tot generally decreasing from crystal cores to marginal areas, and degree of nitrogen aggregation increasing in the same direction. From this, it would follow that in these crystals, the temperature of diamond formation of the outer crystal zones is approximately 40–50 °C higher than that of the inner zones. The same result (15 to 80 °C) was obtained for diamond crystals with cubic habit, which generally show a fibrous internal structure, reflecting normal mechanisms of growth. The anomalous distribution of nitrogen centres in diamond crystals that grew through the normal mechanism, with a high rate of growth and in an oversaturated medium, might point to non-equilibrium relationships between the concentrations of different nitrogen centres. It is likely that in crystals of this type, the rate of growth is higher than the rate of structural nitrogen aggregation. Thus, it appears that in these peculiar crystals of diamond we deal with non-equilibrium concentrations of nitrogen B centres and, consequently, with anomalous, non-actual diamond formation temperatures.     

Petrology and geochemistry of a diamondiferous lherzolite from the Premier diamond mine, South Africa

This paper reports on the petrology and geochemistry of a diamondiferous peridotite xenolith from the Premier diamond mine in South Africa.

The xenolith is altered with pervasive serpentinisation of olivine and orthopyroxene. Garnets are in an advanced state of kelyphitisation but partly fresh. Electron microprobe analyses of the garnets are consistent with a lherzolitic paragenesis (8.5 wt.% Cr₂O₃ and 6.6 wt.% CaO). The garnets show limited variation in trace element composition, with generally low concentrations of most trace elements, e.g. Y (<11 ppm), Zr (<18 ppm) and Sr (<0.5 ppm). Garnet rare earth element concentrations, when normalised against the C1 chondrite of McDonough and Sun (Chem. Geol. 120 (1995) 223), are characterised by a rare earth element pattern similar to garnet from fertile lherzolite.

All diamonds recovered are colourless. Most crystals are sharp-edged octahedra, some with minor development of the dodecahedral form. A number of crystals are twinned octahedral macles, while aggregates of two or more octahedra are also common. Mineral inclusions are rare. Where present they are predominantly small black rosettes believed to consist of sulfide. In one instance a polymineralic (presumably lherzolitic) assemblage of reddish garnet, green clinopyroxene and a colourless mineral is recognised.

Infrared analysis of the xenolith diamonds show nitrogen contents generally lower than 500 ppm and variable nitrogen aggregation state, from 20% to 80% of the ‘B’ form. When plotted on a nitrogen aggregation diagram a well defined trend of increasing nitrogen aggregation state with increasing nitrogen content is observed. Carbon isotopic compositions range from −3.6 ‰ to −1.3 ‰. These are broadly correlated with diamond nitrogen content as determined by infrared spectroscopy, with the most negative C-isotopic compositions correlating with the lowest nitrogen contents.

Xenolith mantle equilibration temperatures, calculated from nitrogen aggregation systematics as well as the Ni in garnet thermometer are on the order of 1100 to 1200 °C.

It is concluded that the xenolith is a fertile lherzolite, and that the lherzolitic character may have resulted from the total metasomatic overprinting of pre-existing harzburgite. Metasomatism occurred prior to, or accompanied, diamond growth.     

An infrared investigation of inclusion-bearing diamonds from the Venetia kimberlite,Northern Province,South Africa : implications for diamonds from craton-margin settings

The Venetia kimberlites in the Northern Province of South Africa sampled diamonds from the lithosphere underlying the Central Zone of the Limpopo Belt. Given the general correlation of diamond-bearing kimberlites with old stable cratons, this tectonic setting is somewhat anomalous and, therefore, it is desirable to characterise the diamonds in terms of their infrared characteristics. A suite of diamonds of known paragenesis from the Venetia mine spans a large range of nitrogen concentrations from less than the detection limit to 1,355 ppm. Diamond nitrogen contents are, on average, higher in the eclogitic diamond population relative to the websteritic and peridotitic diamonds. Nitrogen aggregation states are variable, ranging from almost pure type IaA diamond (poorly aggregated nitrogen) to pure type IaB diamond (highly aggregated nitrogen). On a nitrogen aggregation diagram two distinct groups can be identified based on nitrogen content and nitrogen aggregation state. These are a minor population of diamonds with nitrogen contents generally higher than 500 ppm and nitrogen aggregation states of less than 40% IaB, and another, dominant population that is characterised by higher and more variable nitrogen aggregation. The unusually aggregated nature of the majority of the diamonds analysed is unique to Venetia relative to other intrusives on the Kaapvaal-Kalahari craton, but is similar to aggregation states observed for diamonds from other craton margin or adjacent mobile belt settings such as the Argyle lamproite and the George Creek kimberlite. This could be a consequence of diamond mantle residence at mantle temperatures higher than the norm for other kimberlites from the interior of cratons. Deformation of the mantle, associated with dynamic processes such as orogenesis or subduction, might also be responsible for accelerating the rate of nitrogen aggregation in these diamonds. Low numbers of diamonds with degradation of platelets at the Venetia kimberlite, relative to diamonds from the Argyle lamproite, indicate that deformation was at a significantly lower level. The comparatively low value of diamonds from Argyle (at approximately US8/carat) as opposed to Venetia (US8/carat) as opposed to Venetia (US90/carat) is in large part because of the very high abundance of brown diamonds at Argyle. Therefore, it is apparent that deformational history of the mantle in which the diamonds were resident prior to or during sampling by the host may have an important role to play in the profitability of a primary diamond deposit. The apparently consistent association of diamonds with unusually aggregated nitrogen with kimberlites, or lamproites intruded into craton margin or mobile belt settings suggests that it may be possible to recognise such contributory sources in alluvial diamond deposits, through the study of the infrared characteristics of the diamonds. Electronic supplementary material to this paper can be obtained by using the Springer Link server located at http://dx.doi.org/10.1007/s00410-002-0385-2     

Manifestation of nitrogen interstitials in synthetic diamonds obtained using a temperature gradient technique (Fe–Ni–C system)

The IR-peak 1450 cm^–1 (H1a-center) associated with nitrogen interstitials have been studied in nitrogen-bearing diamonds synthesized at high P-T parameters in the Fe–Ni–C system. FTIR study shows that manifestation of this nitrogen form is restricted to the regions of active transformation of C-defects into A-defects, which confirms the connection of its formation with C => A aggregation process. An examination of the dependence of the 1450 cm^–1 peak on the degree of nitrogen aggregation indicates that H1a-centers are not only formed during C/A aggregation but also disappear simultaneously with the end of C => A transformation. Established facts suggest direct involving of nitrogen as interstitials in the C => A aggregation and serve as strong experimental argument in support of the “interstitial” mechanism of nitrogen migration during aggregation in diamonds containing transition metals.