Cuboid Diamonds Research Articles

Regeneration Growth as One of the Principal Stages of Diamond Crystallogenesis

Revealing the internal structure of diamonds is key to understanding the general regularities of crystal growth and dissolution. This paper presents and summarizes data on the internal structure of diamonds of different morphological types, colors and defect-impurity composition. In order to provide a comprehensive explanation of the stages of diamond growth, crystals and plates were observed, and panchromatic cathodoluminescence and photoluminescence techniques were applied. This article considers the mechanism of tangential growth from existing surfaces (regeneration growth) as an intermediate stage between normal and tangential crystal growth. The regeneration growth is very fast due to the absence of the limiting stage-nucleation of a new atomic layer. Cuboid diamonds were refaceted to stepped octahedrons by the regeneration growth mechanism. A schematic model of crystal habit transformation due to regeneration growth explains the internal structure of crystals in connection with their morphology and thermal history. The main variants of regeneration stage and its morphological manifestations were demonstrated. Most diamonds pass through the regeneration stage, and in many cases, it was a stage of growth termination.

Specific spectroscopic features of yellow cuboid diamonds from placers in the north-eastern Siberian Platform

Specific spectroscopic features of yellow cuboid diamonds from placers in the north-eastern Siberian Platform

The Defect-Impurity Composition of Diamond Crystals with 〈100〉 Growth Pyramids from Placers of the Krasnovishersk District, the Urals

Abstract—The internal structure and spectroscopic features of cuboid diamonds from recent alluvial placers of the Krasnovishersk District (the Urals) have been investigated. Crystals were divided into four groups by their anatomy and spectroscopy: cuboids of the II group (according to the Yu.L. Orlov classification): cuboids with a transparent core and peripheral zone saturated with inclusions; crystals with mixed habit growth of 〈100〉 and 〈111〉 pyramids, and crystals with the sequential growth of 〈100〉 and 〈111〉 pyramids. In all studied crystals, the regenerative formation of the {111} face steps together with the formation of tetragonal pits on the cuboid surface was the last stage of growth. Local photoluminescence investigations have been carried out for all cubic diamond crystals of the Urals for the first time. It was established that luminescence bands at 926 and 933 nm are related to growth pyramids of 〈100〉 and 〈111〉, respectively. Bands with peaks at 800, 820.5, 840, 860, and 869 nm were revealed in the luminescence systems of the cuboids of II group. We note that the cuboid diamonds from different regions of the world have similar internal structures and spectroscopic features.

Structure and Defects in Natural Ballas-Type Diamonds: a Case Study

Structure, defects and inclusions in natural polycrystalline ballas-type diamonds are studied by complementary techniques: Scanning Electron microscopy, cathodo- and photoluminescence, X-ray diffraction, radiography and fluorescence, infra-red spectroscopy and carbon isotope analyses. Peculiarities of internal structure of some of the samples are explained by growth of the diamonds as volume-filling dendrites. Similarities of structure and mineralogy of trapped inclusions between ballas-type diamonds with fibrous and cuboid diamonds are established. However, significant differences between growth mechanisms of all these varieties exist and are possibly explained by variations in carbon supersaturation and diamond wettability by growth medium.

Diamond-forming HDFs tracking episodic mantle metasomatism beneath Nyurbinskaya kimberlite pipe (Siberian craton)

We present a new dataset on the composition of high-density fluids (HDFs) in cloudy (n = 25), coated (n = 10) and cuboid (n = 10) diamonds from the Nyurbinskaya kimberlite pipe. These diamonds represent different populations each showing distinct growth histories. The cores of coated diamonds display multiple growth stages and contrasting sources of carbon. Fibrous coats and cuboid diamonds have similar carbon isotopes and nitrogen systematics, suggesting their formation in the last metasomatic events related to kimberlite magmatism, as is common for most such diamonds worldwide. The HDFs in most of these diamonds span a wide range from low-Mg carbonatitic to hydrous silicic compositions. The major- and trace-element variations suggest that the sources for such HDFs range in composition between the depleted mantle and more fertile mantle reservoirs. Hydrous-silicic HDFs could originate from a 13C-enriched source, which originates through subduction of crustal metasedimentary material. Percolation of such HDFs through carbonated eclogites and peridotites facilitates the formation of cuboid diamonds and fibrous coats in the mantle section beneath the corresponding area of the Siberian craton. Cloudy diamonds represent an apparently older population, reflecting continuous diamond formation predominantly from high-Mg carbonatitic HDFs that caused discrete episodes of diamond precipitation. Their high Mg# and enrichment in incompatible elements support a metasomatized peridotitic source for these HDFs.

The enigma of cuboid diamonds: the causes of inverse distribution of optical centers within the growth zones

The enigma of cuboid diamonds: the causes of inverse distribution of optical centers within the growth zones

Effects of Pitch of Array Punch on the Nanoimprinting

In this study, molecular dynamics (MD) are used to simulate the nanoimprinting behaviors of (001) Ni thin films using 3×3 array cuboid diamond punch. Different pitch of the punches was used to investigate the effect of the interaction among the forming pattern and the quality of the formed holes. Forming force was evaluated including normal and tractional force of the punch during pressing process. The dislocation behavior was also monitoring during the holes forming. The result showed that the pitch of the punch was 2w could get the best forming pattern.

Specific Multiphase Assemblages of Carbonatitic and Al-Rich Silicic Diamond-Forming Fluids/Melts: TEM Observation of Microinclusions in Cuboid Diamonds from the Placers of Northeastern Siberian Craton

The microinclusions in cuboid diamonds from Ebelyakh River deposits (northeastern Siberian craton) have been investigated by FIB/TEM techniques. It was found that these microinclusions have multiphase associations, containing silicates, oxides, carbonates, halides, sulfides, graphite, and fluid phases. The bulk chemical composition of the microinclusions indicates two contrasting growth media: Mg-rich carbonatitic and Al-rich silicic. Each media has their own specific set of daughter phases. Carbonatitic microinclusions are characterized by the presence of dolomite, phlogopite, apatite, Mg, Fe-oxide, KCl, rutile, magnetite, Fe-sulfides, and hydrous fluid phases. Silicic microinclusions are composed mainly of free SiO2 phase (quartz), high-Si mica (phengite), Al-silicate (paragonite), F-apatite, Ca-carbonates enriched with Sr and Ba, Fe-sulfides, and hydrous fluid phases. These associations resulted from the cooling of diamond-forming carbonatitic and silicic fluids/melts preserved in microinclusions in cuboid diamonds during their ascent to the surface. The observed compositional variations indicate different origins and evolutions of these fluids/melts.

Особенности дефектно-примесного состава кристаллов алмаза с пирамидами роста <100> из россыпей Красновишерского района, Урал

The internal structure of cuboid diamonds from contemporary alluvial placers of the Krasnovishersky district at the Urals was investigated with analyzing their spectroscopic characteristics. Crystals were divided into four groups by their anatomy and spectroscopic features: cuboids of the II variety in the Yu. L. Orlov classification; cuboids with transparent core and outer part saturated with inclusions; crystals with simultaneous growth of and pyramids, and crystals with their consecutive growth. The local photoluminescence investigations have been carried out for all different growth zones and pyramids. There was revealed localization of luminescence bands 926 and 933 nm to growth pyramids and . In all studied crystals, the last stage of growth was the regenerative formation of {111} face steps together with square pits forming on the surface. Some cuboids with C centres have specific luminescence systems, such as 575, 635.1, 636.8 nm, broad band with maximum at 700 nm, and intense lines at 800, 820.5, 840, 860, 869 nm. Different thermal history of mixed-habit diamonds was shown. It is noted that the cuboid diamonds from different regions of the world have the similar internal structure and spectroscopic features.

Crystal morphological evolution of growth and dissolution of curve-faced cubic diamonds from placers of the Anabar diamondiferous region

In this paper, we consider an ontogenic model for the formation of morphological types of growth and dissolution of cubic diamonds of variety II by Yu.L. Orlov from placers of the Anabar diamondiferous region. The following ontogenic domains of crystals and corresponding evolutionary stages of growth accompanying a general decrease in supersaturation in the crystallization medium were distinguished: microblock mosaic cuboids with defects produced by the mechanism of rotational plastic deformation–cuboids with linear translation deformations–cuboids and antiskeletal growth forms of cuboids composed of octahedral growth layers–pseudocubic growth forms of a flat-faced octahedron. The crystal morphological evolution of cuboids during the bulk dissolution of individuals in fluid-bearing melt transporting them to the surface was traced. The investigation of transitional forms of cuboid diamond dissolution showed that the final form of diamond dissolution is a rounded tetrahexahedroid independent of the combination of cuboid faces with subordinate faces of octahedron, rhombododecahedron, and tetrahexahedron observed on resorbed crystals of cubic habit. It was found that the final stages of cuboid dissolution produced disk-shaped microrelief features on the diamond surface in the form of randomly distributed ideal rounded etch pits resulting from interaction with microscopic cavitation gas bubbles released during the decompression of ascending kimberlite melt.

The Carbon and Nitrogen Isotope Characteristics of Type Ib-IaA Cuboid Diamonds from Alluvial Placers in the Northeastern Siberian Platform

Cuboid diamonds are particularly common in the placers of the northeastern Siberian platform, but their origin remains unclear. These crystals usually range in color from dark yellow to orange and, more interestingly, are characterized by unusual low aggregated nitrogen impurities (non-aggregated C-center), suggesting a short residence time and/or low temperatures at which they have been stored in the mantle. In order to track possible isotopic signature that could help deciphering cuboid diamond’s crystallization processes, δ13C values, δ15N values, and nitrogen concentrations have been determined in situ in three samples using secondary ion mass spectrometry (SIMS), whereas nitrogen aggregation states have been determined by FTIR spectroscopy. The samples fall out of the δ13C vs. δ15N field of canonical mantle composition. Different scales of carbon and nitrogen fractionation may produce the observed variations. Alternatively, mixing mantle and crustal material would obscure initial co-variations of δ13C values with δ15N or nitrogen content.

The Internal Structure of Yellow Cuboid Diamonds from Alluvial Placers of the Northeastern Siberian Platform

Yellow cuboid diamonds are commonly found in diamondiferous alluvial placers of the Northeastern Siberian platform. The internal structure of these diamonds have been studied by optical microscopy, X-Ray topography (XRT) and electron backscatter diffraction (EBSD) techniques. Most of these crystals have typical resorption features and do not preserve primary growth morphology. The resorption leads to an evolution from an originally cubic shape to a rounded tetrahexahedroid. Specific fibrous or columnar internal structure of yellow cuboid diamonds has been revealed. Most of them are strongly deformed. Misorientations of the crystal lattice, found in the samples, may be caused by strains from their fibrous growth or/and post-growth plastic deformation.

Nitrogen and hydrogen aggregation in natural octahedral and cuboid diamonds

Nitrogen and hydrogen aggregation in natural octahedral and cuboid diamonds

Composition of diamond-forming media in cuboid diamonds from the V. Grib kimberlite pipe (Arkhangelsk province, Russia)

Composition of diamond-forming media in cuboid diamonds from the V. Grib kimberlite pipe (Arkhangelsk province, Russia)

Regular cuboid diamonds from placers on the northeastern Siberian platform

Alluvial placers of the northeastern Siberian Platform are characterized by a specific diamond population: regular cuboids, forming a continuous color series from yellowish-green to yellow and dark orange. This is the first comprehensive study of a large number of cuboid diamonds focusing on their morphology, N content and aggregation state, photoluminescence, C isotopic composition and inclusions.The cuboids are cubic (i.e. nearly flat faced) to subrounded crystals; most of them are resorbed. The cathodolominescence images and the birefringence patterns show that many cuboid diamonds record deformation. The cuboid diamonds are characterized by unusual FTIR spectra with the presence of C- (single nitrogen atom) and A- (pair of neighbour nitrogen atoms) centers, and two centers of unknown origin, termed X and Y. The presence of single substitutional nitrogen defects (C centers) in all cuboid diamonds testifies either storage in the mantle at relatively cool conditions or formation just prior to eruption of their host kimberlites. The studied diamonds are also characterized by the presence of specific set of luminescence centers: N3, H3, S1, NVo and NV−, some of which are suggested to have formed during deformation subsequent to diamond growth. The cuboid diamonds show a wide range of carbon isotope compositions from mantle-like values towards strongly 13C depleted compositions (−6.1 to −20.2‰ δ13C). Combined with the finding of an eclogitic sulfide inclusion, the light carbon isotope compositions link the formation of the studied cuboids to deeply subducted basic protoliths, i.e. former oceanic crust.

Trace element partitioning in mixed-habit diamonds

Mixed-habit diamonds are a special type of crystal that form by simultaneous growth by two different mechanisms; octahedral and cuboid growth. This type of crystal growth is known to preferentially partition nitrogen into the octahedral growth sectors during growth. To identify if this fractionation occurs for any other trace element, this study applies in situ laser ablation mass spectrometry to a well-studied collection of mixed-habit diamonds. The results show high concentrations of nickel (3.6–36.4ppm) and cobalt (0.108–1.25ppm) in the cuboid sectors, whereas the octahedral sectors contain only <0.05–0.35ppm nickel and <0.014–0.03ppm cobalt. The relative enrichment of nickel in the cuboid sectors varies between 10 and 460 times. For cobalt, where the concentrations in the octahedral sector are commonly below the limit of quantification, the enrichment is estimated to be in the range of 10–100 times. There appears to be a rough linear relationship between the concentrations of the two elements in the cuboid sectors, with nickel concentrations approximately 27 times that of cobalt. This finding of nickel fractionation into the cuboid sectors is the opposite of what is seen in synthetic diamonds grown from FeNi solvents, where Ni is only found in the octahedral growth sectors. We propose that this is because the inherent lattice strain in the rough cuboid diamond growth of natural mixed-habit diamonds is greater than that in the smooth octahedral growth, making it easier to fit the large Ni and Co ions into a divacancy. In diamonds grown from metal solvents (i.e. industrial synthetic diamonds), the cube face is a smooth one, therefore the partitioning of trace elements is simply a result of the octahedral surface offering more bonding opportunities than the cube surface.Due to the extremely low concentrations of trace elements in these gem quality diamonds, many of the elements are commonly below the limit of quantification (LOQ). While we are confident that Pr, Sr, Pb, Zr, V, Cr and Zn are not fractionated by the crystal growth mechanisms of mixed-habit diamonds that affect Ni and Co, this remains to be proven for the remaining trace elements analysed. Data on the fractionation of copper are inconclusive, with 75% of data from the cuboid sectors above the LOQ and all data from the octahedral sectors below the LOQ. However, the values of the LOQ for the octahedral data are often higher than those of the cuboid data, so further investigation of Cu is necessary to confirm its behaviour.

Platelet development in cuboid diamonds: insights from micro-FTIR mapping

Fourier transform infrared mapping of diamonds can reveal detailed information on impurities, with a spatial context. We apply this technique, combined with in situ isotopic analysis of carbon, to the study of cuboid diamond growth in a sample that exhibits some mixed-habit growth. While there has been some uncertainty in the literature regarding sectoral differences in nitrogen aggregation and subsequent platelet development, the data from this study appear far more conclusive. We show that despite nitrogen being concentrated in octahedral sectors, there is no detectable difference in the concentration-adjusted rate of nitrogen aggregation within octahedral and cuboid sectors. However, the resultant platelet development is significantly reduced in cuboid sectors compared to contemporaneously formed octahedral sectors. This finding has significant implications for the classification of diamonds using the relationship between their platelet intensity and the absorption caused by B centres. It means that cuboid diamonds naturally fall below the linear relationship that has been termed regular, which would lead to them being incorrectly interpreted as having experienced heating or deformation. The data also support earlier suggestions that large hydrogen concentrations in the diamond-forming fluid may be required for cuboid growth. We further suggest that high nitrogen and hydrogen concentrations are required for mixed-habit diamond growth, which might be the product of specific fluid chemistries that occur in reducing mantle environments.

Diamonds through Time

Diamonds form in the upper mantle during episodic events and have been transported to the Earth’s surface from at least the Archean to the Phanerozoic. Small diamonds occur as inclusions in robust minerals in tectonically activated, ultrahigh-pressure metamorphosed crustal rock, establishing an association with subduction processes and recycled carbon, but providing no economic deposits. Diamonds in economic deposits are estimated to be mainly (99%) derived from subcontinental lithospheric mantle and rarely (approx. 1%) from the asthenosphere. Harzburgite and eclogite are of roughly equal importance as source rocks, followed by lherzolite and websterite. Diamonds which provide evidence of extensive residence time in the mantle are, with minimal exceptions, smooth-surfaced crystalline diamonds (SCD) with potential commercial value. The oldest prolific SCD formation event documented on the world’s major diamond producing cratons occurs in Archean lithospheric mantle harzburgite, metasomatized by likely subduction-related potassic carbonatitic fluids. Disaggregation of the diamondiferous carbonated peridotite on decompression during volcanic transit gives rise to the association between diamonds, G10 garnets, and diamond inclusion-type chromites, well used in diamond exploration. Within the mantle domains of diamond stability, there have been repeated episodes of further diamond crystallization and/or growth. These are associated with old, often Proterozoic, subduction-related melt generation, metasomatic fluid migration, and reaction with preexisting mantle eclogite, websterite, and peridotite. Using improved methods of isotope analysis, diamond formation ages can be correlated with specific major processes such as craton accretion, craton edge subduction, and magmatic mantle refertilization. Fibrous cuboid diamond and fibrous coats on SCD are rough-surfaced diamonds with abundant fluid inclusions. They have low mantle residence time, forming rapidly from late stage metasomatic fluids in diamond stable domains that may already contain SCD. The symbiotic relationship between formation of fibrous diamond and magmatic sampling and transport of diamonds into the crust suggest that the associated fluids contribute diamond-friendly volatile loading of the deep lithospheric mantle shortly before the triggering of a volcanic eruption, continuing a process of volatile enrichment in the lithospheric mantle already identified in the Archean harzburgite diamond event. Mantle-derived SCD commonly shows evidence of resorption, illustrating that diamond-unfriendly processes, including lamproite and kimberlite generation, are also active and may have a substantial negative effect in extreme cases on SCD crystal size. Exposure of SCD to a long period of changing conditions during mantle residence contributes to the difficulty of assigning specific parageneses and ages to individual inclusion-free diamonds with our current state of knowledge.

Mg and Fe-rich carbonate–silicate high-density fluids in cuboid diamonds from the Internationalnaya kimberlite pipe (Yakutia)

Microinclusions in 44 cuboid diamonds from the Internationalnaya kimberlite pipe (Yakutia) show wide compositional variations. In comparison with the available worldwide database most microinclusions in diamonds from Internationalnaya define a continuous range of compositions from carbonatitic to hydrous-silicic high-density fluids (HDFs). The hydrous-silicic compositional range is reported here for the first time in Yakutian diamond-forming fluids. The hydrous-silicic end-members are rich in water, SiO 2, Al 2O 3, K 2O and P 2O 5. Carbonatitic end-members are rich in carbonate, CaO, MgO, Na 2O and FeO. Microinclusions in diamonds from Internationalnaya show a range from magnesian to extremely iron-rich compositions. There are two compositional arrays of microinclusions: (i) carbonate-rich with SiO 2 < 10 wt.% where FeO decreases without any correlation with sulfur, water, carbonate or chlorine and (ii) carbonatitic to hydrous-silicic where FeO generally decreases as SiO 2 contents increase. The trace-element patterns of the microinclusions are generally similar to those of kimberlites and carbonatites, but there are significant differences in the major elements. The relative abundance of K in the microinclusions is significantly higher. The microinclusions have smooth patterns for the LILE, normalized to a primitive mantle composition. HFSE patterns in the microinclusions show some depletion in Ti, Zr and Hf relative to Ta, Nb and Mo. Primitive mantle normalized REE patterns reveal low abundances of the heavy REE and high concentrations of light REE. The La/Dy ratio of microinclusions varies widely, decreasing from carbonatitic to hydrous-silicic compositions. A general correlation of δ 13C of diamonds with the relative abundance of carbonates in the microinclusions suggests that carbon isotope compositions are related to the evolution of the parental media. The carbonate–silicate range of high-density fluids observed in diamonds from Internationalnaya may be explained by fractional crystallization of mantle fluids/melts, or mixing between liquids with different compositions.

Composition of trapped fluids in cuboid fibrous diamonds from the Udachnaya kimberlite: LAM-ICPMS analysis

The bulk major- and trace-element compositions of micro-inclusions in 24 cuboid diamonds from the Udachnaya kimberlite pipe (Siberia, Russia) have been quantitatively analyzed by Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LAM-ICPMS). Micro-inclusions in the studied diamonds represent a bulk sample of the fluids from which the diamonds crystallized; they define a continuous range between magnesian and calcic carbonate-rich compositions at relatively constant Fe contents (Ca/(Ca + Mg) = 0.31–0.68; Mg/(Mg + Fe) = 0.66–0.78). In general the major- and trace-element patterns of the trapped fluids in Udachnaya cuboid diamonds are similar to those of kimberlites and carbonatites. However, some important differences are observed: (1) the fluids in diamonds are enriched in K, Na, Fe and depleted in Al relative to the host kimberlite; (2) the REE patterns of the fluids are steeper than those of kimberlites; (3) many of the fluids show strong depletion in Ti, Zr and Y. The observed geochemical features are consistent with a genetic link between the diamond-forming fluids and ephemeral carbonatitic fluids/melts which may be precursors of the host kimberlite. These fluids/melts may originate either from the metasomatic and influx of carbonatitic agents or from partial melting of previously carbonated eclogites and peridotites. Some elemental variations may be explained by fractional crystallization of such fluid/melts, or mixing between fluids with different compositions.