Well-crystallized Graphite Research Articles

New, 3D binder-jetted carbons with minimal periodic surface structures

This study focuses on the design, additive manufacturing, and characterization of porous carbon-based structures in the form of a triply periodic minimal surface (TPMS) with outstanding mechanical properties and oxidation resistance, combined with good electrical and thermal conductivity. Binder jetting (BJ) of graphite-carbon black powders was used to 3D print computational models of three TPMS with different topologies and geometric porosities. Infiltration and pyrolysis (PIP) with furan resin was then performed to densify the parts. Composite materials, comprising a highly disordered carbon matrix binding well-crystallized graphite grains, were obtained. The printed and pyrolyzed samples are highly porous TPMS cylinders with diameter, height and a surface thickness of ∼19 mm, ∼33 mm and 0.76 mm, respectively. The samples have a skeleton intrinsic porosity of 20%, of which 8% is open, meaning that the material could potentially be further infiltrated and densified. Nevertheless, the samples have better mechanical properties than compressed carbon-graphite composites, as well as 3D-printed carbon produced by direct ink writing and stereolithography. High-temperature tests showed that, although the amorphous carbon matrix is more prone to oxidation than the graphite grains, the overall oxidation resistance remains exceptionally high. These properties allow for applications as Joule resistors and in seasonal thermal storage.

XRD-based crystallinity degrees and formation temperature of graphite in some regional-metamorphic rocks from the Central and Eastern Rhodopes, Bulgaria: a test of the new graphitization degree GD(0–30) scale

Graphitization degrees and temperatures of the regional metamorphism in the Central and Eastern Rhododpes have been determined by the values of the structural parameter d002 (Å) of graphite in graphite-bearing marbles and shists, from Vacha and Madan-Erma Reka areas (Madan lithotectonic unit), Ardino–Nedelino area (Startsevo lithotectonic unit), and Chernichevo–Boturche area (Byala Reka lithotectonic unit). Equations of different authors, formulated between 1951 and 2021, were used. They are integrated in one system, allowing a conversion of the results and deriving new quantitative correlations between the temperature of metamorphism, the structural parameter d002 (Å) and the degree of crystallinity order of semi-graphite and graphite. The comparison of the data allows the creation of a new scheme, GD(0–30), based on the values of the parameter d002 (Å) of the natural carbon matter. The validity range of this geothermometer is large, from 84 °C to 804 °C (from zeolite to granulite facies of the regional metamorphism). The temperature peak of metamorphism in the studied areas is 660 °C (i.e., the upper limit of the amphibolite facies), and the lowest temperature is 468 °C, which is characteristic for the lower part of the greenschist facies P-T field. The temperature range and graphitization degrees of the regressive metamorphism in the Central and Eastern Rhodopes are: 660 °C (GD(0–30) = 24, well-crystallized graphite); 588 °C (GD(0–30) = 21, graphite); 564 °C (GD(0–30) = 20, graphite); 516 °C (GD(0–30) = 18, graphite); 492 °C (GD(0–30) = 17, graphite); and 468 °C (GD(0–30) = 16, graphite). The calculated temperatures of metamorphism in the Central and Eastern Rhodopes, by equations of all authors, correspond to the conditions of metamorphism established by other methods without using of the structural parameter d002 (Å) of the graphite. The GD(0–30) system for determination of graphitization degree of the natural carbon is simple, informative and functional. It is more convenient than earlier schemes showing correlation: metamorphic temperature − d002 (Å) − graphitization degree. In addition to the influence of the temperature, the values of the degrees of graphitization also include the effect of all secondary factors on the graphitization processes.

Catalytic graphitization of single-crystal diamond

Diamond and graphene are carbon allotropes with starkly different physical characteristics. Their combination into graphene-on-diamond heterostructures could benefit from the complementary properties of both components. Graphitization of single-crystalline diamond surfaces is a promising synthesis route, but a clear understanding of the growth of graphene or graphite from solid carbon sources is so far missing. Using aberration-corrected transmission electron microscopy, Raman spectroscopy, and electrical transport measurements, we provide detailed insight in the mechanisms of structural changes of nickel-catalyzed graphitization of diamond. We propose competing atomistic processes occurring at contact sites of diamond and Ni, depending on diamond surface terminations. One-dimensional etching process dominates on (111) diamond surfaces that remain almost atomically flat during graphitization. Two-dimensional etching of (110) and (100) diamond surfaces results in Ni drilling into the diamond substrate. Our findings also provide evidence on the reaction rates of the catalysis. The most reactive diamond surface in the (100) orientation is covered with the largest amount of well-crystallized graphite, whereas the (111) surface shows the highest stability against catalytic etching. In the latter case, only a thin disordered graphite layer is formed, yielding the lowest electric conductance. By clarifying these etching mechanisms, our results can improve the synthesis of graphene-on-diamond heterostructures.

Genesis of the Tianping flake graphite deposit at the western margin of Yangtze Block, SW China

The Tianping flake graphite deposit is located in the western margin of the Yangtze Block, South China. It is one of the biggest and representative flake graphite deposits with 8 million tons of flake graphite in the Kangdian Axis graphite metallogenic belt. The graphite orebodies are hosted in graphite schist and mica quartz schist. Carbon isotope data for graphite ore show light carbon values between −26.3‰ to −28.8‰ which suggests a biogenic origin. The carbonaceous materials of the Tianping graphite deposit were deposited younger than ca. 833 Ma according to U-Pb dating results of detrital zircons in graphite samples. The calculated metamorphic temperature of graphite from Raman spectra is between 414 and 436 ± 50 °C, indicating a greenschist to amphibolite facies metamorphism is responsible for the transformation of disordered carbonaceous matter into well-crystallized graphite. After carbonaceous material deposition and graphite formation by regional metamorphism, the graphite may recrystallize and form large graphite flakes in a heated environment brought by the intrusion of plutons in the region. Based on previous studies and new data, a three-stage genesis model including processes of material deposition, regional metamorphism, later magmatism, and contact metamorphism for Tianping flake graphite deposit is proposed.

Graphene-reinforced polymer matrix composites fabricated by in situ shear exfoliation of graphite in polymer solution: processing, rheology, microstructure, and properties

Effective methods are needed to fabricate the next generation of high-performance graphene-reinforced polymer matrix composites (G-PMCs). In this work, a versatile and fundamental process is demonstrated to produce high-quality graphene-polymethylmethacrylate (G-PMMA) composites via in situ shear exfoliation of well-crystallized graphite particles loaded in highly-viscous liquid PMMA/acetone solutions into graphene nanoflakes using a concentric-cylinder shearing device. Unlike other methods where graphene is added externally to the polymer and mixed, our technique is a single step process where as-exfoliated graphene can bond directly with the polymer with no contamination/handling. The setup also allows for the investigation of the rheology of exfoliation and dispersion, providing process understanding in the attainment of the subsequently heat injection-molded and solidified G-PMC, essential for future manufacturing scalability, optimization, and repeatability. High PMMA/acetone concentration correlates to high mixture viscosity, which at large strain rates results in very-high shear stresses, producing a large number of mechanically-exfoliated flakes, as confirmed by liquid-phase UV–visible spectral analysis. Raman spectroscopy and other imaging evince that single- and bi-layer graphene are readily achieved. Nevertheless, a limit is reached at high mixtures viscosities where the process becomes unstable as non-Newtonian fluid behavior (e.g. viscoelastic) dominates the system. Characterization of microstructure, morphology, and properties of this new class of nanostructured composites reveals interesting trends. Observations by transmission electron microscopy, scanning electron microscopy, and helium ion microscopy of the manufactured G-PMCs show uniform distributions of unadulterated, well-bonded, discontinuous, graphene nanoflakes in a PMMA matrix, which enhances stiffness and strength via a load-transfer mechanism. Elastic modulus of 5.193 GPa and hardness of 0.265 GPa are achieved through processing at 0.7 g ml−1 of acetone/PMMA for 1% wt. starting graphite loading when injected into a sample mold at 200 °C. Mechanical properties exhibit 31% and 28.6% enhancement in elastic modulus and hardness, respectively, as measured by nano-indentation.

Microstructures and mechanical properties of TiB2-based composites with self-grown carbon nanotubes synthesized using Co catalysts

Carbon nanotubes (CNTs) were grown on TiB2 powder by chemical vapor deposition using a Co catalyst. Then, the bulk CNTs(Co)-TiB2 composite was consolidated from these in-situ synthesized powder by spark plasma sintering. Homogeneously-dispersed CNTs with herringbone-like structure composed of well-crystallized graphite were observed. The flexural strength and fracture toughness of the in-situ synthesized CNTs(Co)-TiB2 composite were determined to be 987 ± 42 MPa and 12.4 ± 0.5 MPa m1/2 respectively, which were much higher than those of monolithic TiB2 and TiB2-CNTs composites synthesized by traditional ball-milling and sintering. The improvement of the composite performance was ascribed to the hybrid effect of the fully dense structure of the composite, the appropriate interfacial strength between the CNTs and the matrix, and the higher strengthening ability of well-dispersed CNTs.

Raman spectral characteristics of magmatic-contact metamorphic coals from Huainan Coalfield, China

Normal burial metamorphism of coal superimposed by magmatic-contact metamorphism makes the characteristics of the Raman spectrum of coal changed. Nine coal samples were chosen at a coal transect perpendicular to the intrusive dike, at the No. 3 coal seam, Zhuji Coal Mine, Huainan Coalfield, China, with different distances from dike-coal boundary (DCB). Geochemical (proximate and ultimate) analysis and mean random vitrinite reflectance (R0, %) indicate that there is a significant relationship between the values of volatile matter and R0 in metamorphosed coals. Raman spectra show that the graphite band (G band) becomes the major band but the disordered band (D band) disappears progressively, with the increase of metamorphic temperature in coals, showing that the structural organization in high-rank contact-metamorphosed coals is close to that of well-crystallized graphite. Evident relationships are observed between the calculated Raman spectral parameters and the peak metamorphic temperature, suggesting some spectral parameters have the potentials to be used as geothermometers for contact-metamorphic coals.

Microstructural evolution of carbonaceous material during graphitization in the Gyoja-yama contact aureole: HRTEM, XRD and Raman spectroscopic study

Graphitization of carbonaceous material (CM) in the Gyoja-yama contact aureole, northwest of Kyoto, Japan, was examined using high-resolution transmission electron microscopy (HRTEM), X-Ray Diffractometry (XRD), and Micro-Raman spectroscopy. In this region, the CM in the sedimentary rocks has been transformed from poorly crystalline to well-crystallized graphite. This conversion is evident from its morphological transformation of the grain structure to filament like structure and finally into hexagonal plate structure. These microstructural evolutions closely resemble the graphitization process that is usually observed in regional metamorphism, as reported in previous HRTEM observations. Micro-Raman and XRD results indicate that the graphitization parameters are also comparable to each other, where Lc(002) and La(110) values increase during graphitization in contact metamorphism. However, the d002 values have lower correlation coefficients with R2 compared to other parameters. In addition, the crystal size of fully ordered graphite with a d-spacing of ≤3.36 A in contact metamorphic rocks is approximately 100 A larger than that in regional metamorphic rocks. These features indicate that information of d002 parameter includes not only the peak metamorphic temperature condition, but also several other factors such as deformation, confining pressure, impurities of fluid activities and catalytic effect, which may be the key point to fully understand the evolution of CM to graphite.

Nano-polycrystalline diamond formation under ultra-high pressure

Well-crystallized graphite and high energy ball-milled graphite were treated under 16GPa and temperatures up to 2500°C. Our experiments indicated that the ball-milled graphite can completely transform to nano-polycrystalline diamond (NPD) at 2100°C, while the well-crystallized graphite required 2500°C. The samples were characterized by X-ray diffraction, optical microscope, scanning electron microscope, and Vickers indenter hardness test. We found that high pressure not only made the conversion of graphite to NPD thermodynamically preferred, but also reduced the needed activation energy barrier. By analyzing thermodynamics and kinetics of the transformation, we suggested a low boundary for NPD forming region based on the phase diagram of carbon, and the formation mechanisms of Nano-polycrystalline diamond.

Preparation of cohesive graphite films by electroreduction of CO32 − in molten Na2CO3–NaCl

Synthesis of graphite films on 304 stainless steel (304SS) with and without multi-arc ion plated Cr and Ti coating by galvanostatic electroreduction of carbonate ions in molten 0.2Na2CO3–0.8NaCl (in mole fraction) has been investigated at 900°C in argon gas, and the deposits were examined by scanning electron microscopy and Raman spectroscopy. The experimental results indicated that the carbon deposits obtained on both the Cr-coated and Ti-coated 304SS at the constant current density of 192mAcm−2 were continuous and exhibited a compact structure, with an excellent bonding with the substrate, while that obtained on the bare 304SS was porous and exhibited a poor adhesion to the substrate. Raman spectroscopy measurements showed that the carbon deposits on 304SS were mainly composed of amorphous carbon, with a small amount of graphitic crystallites, whereas the carbon films deposited on the Cr and Ti-coated 304SS consisted of well-crystallized graphite. The microstructure of ion plated coatings is helpful to the nucleation and growth of a well-crystallized graphite film.

Low-temperature synthesis of multi-walled carbon nanotubes over Cu catalyst

It is well known that Fe, Co, Ni, and their alloy are the effective catalyst components in chemical vapor deposition growth of carbon nanotubes (CNTs), while Cu has low catalytic activity owing to its nearly zero carbon solubility. In this paper, a simple and effective approach was developed to synthesize multi-walled CNTs using unmodified Cu catalyst supported on Al matrix under a low temperature (600°C). The obtained CNTs with bamboo-like structure are mainly composed of well-crystallized graphite. It is found that the Al carrier plays a key role in the catalytic growth of CNTs, signifying a new way for low-temperature synthesis of multi-walled CNTs.

Processing and mechanical properties of carbon nanotube–alumina hybrid reinforced high density polyethylene composites

Carbon nanotube–alumina hybrid reinforced high density polyethylene (HDPE) matrix composites were prepared by melt processing technique. Microstructure studies verified that the nanotubes consisting of well-crystallized graphite formed a network structure with Al 2O 3 in the hybrid, which was homogeneously dispersed in the HDPE matrix composites. Mechanical measurements revealed that 5% addition of nanotube–alumina hybrid results in 100.8% and 65.7% simultaneous increases in Young's modulus and tensile strength, respectively. Fracture surface showed homogenous dispersion of nanotubes and Al 2O 3 in the HDPE matrix and presence of interlocking like phenomena between hybrid and HDPE matrix, which might contribute to the effective reinforcement of the HDPE composites.

Relationship between structure, morphology, and carbon isotopic composition of graphite in marbles: Implications for calcite-graphite carbon isotope thermometry

Carbon isotope exchange between calcite and graphite is a useful and reliable geothermometer for medium- to high-grade marbles. However, in rare instances, such as at Naxos, Greece, apparent disequilibrium carbon isotope fractionation between calcite and graphite has been previously reported. In this study, new results are presented on the morphological features, X-ray diffraction studies, Raman spectroscopic studies, and carbon isotope studies of graphite. Three morphologically distinct graphite types are identified. The first type is fine grained with distinct polygonal crystal aggregates having smooth pinacoid faces. The second type consists of large botryoidal aggregates with typical crystal overgrowth features, and the third type is “normal” large platy crystals associated with phlogopite. Graphite morphological features using an FE-SEM suggests that the botryoidal aggregates are composed of complexly intergrown and stacked graphite layers, comprised of cone-helix structures. Different types of graphite display distinct Lc(002) and DG values as well as a sharp first-order Raman peak at ~1580 cm −1 with disordered bands. The presence of Raman disordered bands in fine-grained well-crystallized graphite is attributed to edge effects. Carbon isotope analysis of graphite reveals that marble with fine-grained well-crystallized graphite show a consistent isotope fractionation with the calcite, which perfectly match temperature estimates based on the mineral isograds. In contrast, coarse botryoidal graphite gives heterogeneous carbon isotope values (about a few per mill) and show anomalous carbon isotope fractionation between the calcite and graphite. The graphite associated with phlogopite also shows variations in the carbon isotope values. Combining morphologic, crystallographic, and carbon isotopic data we conclude that the variations in carbon isotopic composition were caused by the overgrowth of graphite on the preexisting grain and that morphological observations and structural characterizations of graphite crystals is a key for predicting isotopic equilibration during metamorphism.

Ancient graphite in the Eoarchean quartz-pyroxene rocks from Akilia in southern West Greenland II: Isotopic and chemical compositions and comparison with Paleoproterozoic banded iron formations

We present detailed petrographic surveys of apatite grains in association with carbonaceous material (CM) in two banded iron formations (BIFs) from the Paleoproterozoic of Uruguay and Michigan for comparison with similar mineral associations in the highly debated Akilia Quartz-pyroxene (Qp) rock. Petrographic and Raman spectroscopic surveys of these Paleoproterozoic BIFs show that apatite grains typically occur in bands parallel to bedding and are more often associated with CM when concentrations of organic matter are high. Carbonaceous material in the Vichadero BIF from Uruguay is generally well-crystallized graphite and occurs in concentrations around 0.01 wt% with an average δ 13C gra value of −28.6 ± 4.4‰ (1 σ). In this BIF, only about 5% of apatite grains are associated with graphite. In comparison, CM in the Bijiki BIF from Michigan is also graphitic, but occurs in concentrations around 2.4 wt% with δ 13C gra values around −24.0 ± 0.3‰ (1 σ). In the Bijiki BIF, more than 78% of apatite grains are associated with CM. Given the geologic context and high levels of CM in the Bijiki BIF, the significantly higher proportion of apatite grains associated with CM in this rock is interpreted to represent diagenetically altered biomass and shows that such diagenetic mineral associations can survive metamorphism up to the amphibolite facies. Isotope compositions of CM in muffled acidified whole-rock powders from the Akilia Qp rock have average δ 13C gra values of −17.5 ± 2.5‰ (1 σ), while δ 13C carb values in whole-rock powders average −4.0 ± 1.0‰ (1 σ). Carbon isotope compositions of graphite associated with apatite and other minerals in the Akilia Qp rock were also measured with the NanoSIMS to have similar ranges of δ 13C gra values averaging −13.8 ± 5.6‰ (1 σ). The NanoSIMS was also used to semi-quantitatively map the distributions of H, N, O, P, and S in graphite from the Akilia Qp rock, and relative abundances were found to be similar for graphite associated with apatite or with hornblende, calcite, and sulfides. These analyses revealed generally lower abundances of trace elements in the Akilia graphite compared to graphite associated with apatite from Paleoproterozoic BIFs. Graphite associated with hornblende, calcite, and sulfides in the Akilia Qp rock was fluid-deposited at high-temperature from carbon-bearing fluids, and since this graphite has similar ranges of δ 13C gra values and of trace elements compared to graphite associated with apatite, we conclude that the Akilia graphite in different mineral associations formed from the same source(s) of CM. Collectively our results do not exclude a biogenic origin of the carbon in the Akilia graphite, but because some observations can not exclude graphitization of abiogenic carbon from CO 2- and CH 4-bearing mantle fluids, there remain ambiguities with respect to the exact origin of carbon in this ancient metasedimentary rock. Accordingly, there may have been several generations of graphite formation along with possibly varying mixtures of CO 2- and CH 4-bearing fluids that may have resulted in large ranges of δ 13C gra values. The possibility of fluid-deposited graphite associated with apatite should be a focus of future investigations as this may prove to be an alternative pathway of graphitization from phosphate-bearing fluids. Correlated micro-analytical approaches tested on terrestrial rocks in this work provide insights into the origin of carbon in ancient graphite and will pave the way for the search for life on other ancient planetary surfaces.

Carbon materials in Antarctic and nonAntarctic carbonaceous chondrites: high-resolution transmission electron microscopy

Carbon materials from eight Antarctic carbonaceous chondrites (CM2, CO3, and CV3 types) and two nonAntarctic carbonaceous chondrites (CM2 and CV3 types) were studied using a high-resolution transmission electron microscope (HRTEM). Nanodiamonds and “carbonaceous globules” were found in seven of the Antarctic chondrites and one nonAntarctic CM2 chondrite. These results suggest that nanodiamonds and carbonaceous globules are common in carbonaceous chondrites. The finding of carbonaceous globules in the meteorites that experienced post-hydration high-temperature thermal metamorphism suggests that they are resistant to thermal metamorphism. Well-crystallized graphite was mainly found in the CV3- and CO3-type chondrites, whereas poorly crystallized graphite was mainly found in the CM2-type chondrites. The CM2-type chondrites also contain characteristic carbon structures that are similar to tetrahedral carbon onions and multilayered fullerene. In this study, we discuss the origin of these types of carbon material.

A practical method for the production of hollow carbon onion particles

Carbon onions with diameters ranging from 5 to 50 nm and carbon-coated nickel nanoparticles with diameters ranging from 10 to 60 nm have been synthesized on a large scale over Ni/Al catalyst by chemical vapor deposition. The approximate ratio of Ni-filled to empty onions as observed by TEM is 1:3.5. In order to eliminate the nickel nanoparticle and obtain pure hollow carbon onions, HNO 3 acid was used to dissolve the nickel from the carbon-coated nickel nanoparticles. The carbon onion particles thus obtained have hollow cores and are mainly composed of well-crystallized graphite, as characterized by high-resolution TEM and Raman spectroscopy. In addition, we proposed a simple purification mechanism for Ni-filled carbon onions based on TEM observations.

Carbonization and graphitization of shavings filed away from Kapton

Two kinds of shavings with different degrees of defect concentration were filed away from Kapton with 50 μm in thickness using two sheets of diamond paper with different diamond particle size. Kapton is known as a starting material for preparation of well-crystallized graphite film. The shavings were carbonized and their graphitization behaviors were investigated by X-ray diffraction and Raman microprobe measurements. The carbonized shavings heat-treated at 3000 °C show lower graphitizability than that of the carbonized Kapton film heat-treated at 3000 °C. Existence of turbostratic structure in the 3000 °C-treated shavings was verified by X-ray diffraction. The results of the Raman microprobe on the 3000 °C-treated shavings indicated inhomogeneous graphitization proceeded during heat treatment. The graphitization degree of the 3000 °C-treated shavings has been found to depend on the average size of the diamond particles of the diamond paper used.

ELECTROCHEMICAL STORAGE OF HYDROGEN IN CARBON NANOSTRUCTURES

We have synthesized a set of nanostructured carbon samples including a variety of carbon nanotubes and carbonaceous particles, by catalytic thermal decomposition of CH4 on catalyst LaNi 5 powder with different reaction temperatures. Products obtained at reaction temperatures 550~900°C were characterized by means of HR-TEM, SEM and Raman Scattering. In addition, electrochemical charge–discharge cycling method was carried out at room temperature to measure the reversible hydrogen capacity in pressed electrodes containing mixture of catalyst, nanostructured carbon samples and carbonaceous particles. Results showed that the abundance ratio of well-crystallized graphite to amorphous carbon in each product increases with increasing reaction temperatures. This preliminary study showed also that the hydrogen storage capacity of synthesis products measured in an electrochemical half-cell at room temperature correlates with the nanostructure and morphology of the variety of nanostructured carbon samples. Additionally, the hydrogen adsorption capacity against specific surface area (BET) for synthesis products produced at temperatures higher than 670°C is ranging from 14 to 25 wt.%/(1000 m2/g).

Formation of graphite crystals at 1000–1200°C from mixtures of vinyl polymers with metal oxides

The formation of graphite crystals from mixtures of different carbon precursors, poly(vinyl chloride) (PVC), poly(vinyl alcohol) (PVA) and poly(vinyl pyrrolidone) (PVP), with iron oxides Fe 3O 4 and Fe 2O 3, nickel oxide NiO, cobalt oxide Co 3O 4 and iron powder was studied at a temperature between 800 and 1200°C. The formation of flaky graphite crystals was confirmed from X-ray diffraction and transmission electron microscopy, and the reaction mechanism was studied by differential thermal analysis. From the powder mixtures of vinyl polymers, PVC, PVA and PVP, with Fe 2O 3, Fe 3O 4, Fe and Co 3O 4, graphite was obtained by the heat treatment at the temperature above 1000°C for 1 h, the higher temperature and the longer residence time giving the higher crystallinity of graphite. However, the mixture of NiO with PVA behaved a little different; well-developed turbostratic structure at 1000°C for 1 h and well-crystallized graphite at 1100°C for 24 h. The formation of graphite crystals was supposed to occur through the following steps; thermal decomposition and carbonization of vinyl polymers below 500°C, reduction of metal oxides to metal by carbonaceous products and then catalytic action of metals to precipitate graphite. Since carbons were consumed for the reduction of metal oxides, the mixing ratio of PVA to metal oxides suitable for the formation of graphite crystals was found to be related to the oxidation state of metals.

Origin of Proterozoic metal-rich black shales from the Bohemian Massif, Czech Republic

Proterozoic metal-rich black shales (metasiltstones) in the Bohemian Massif are always closely associated with submarine mafic volcanic rocks and occur in (semi)isolated basins that formed most likely in connection with the evolution of an Upper Proterozoic intracontinental rift. The black shales are characterized by an average of 3.5 wt percent C organic , and 5.2 wt percent S and carry up to 0.42 wt percent Zn, 0.21 wt percent V, 0.12 wt percent Ni, 0.12 wt percent Cr, 0.12 wt percent Cu, 0.06 wt percent As, 0.03 wt percent Mo, 132 ppb Au, 102 ppb Pd, 25 ppb Pt, 1.7 ppb Rh, and 1.3 ppb Ru. Their thickness varies from about 1 to 45 m. Sulfide minerals often include abundant framboidal pyrite, which occurs widely in C organic -rich layers. Grainy pyrite, Zn, Ni, Cu, and Mo sulfides appear to be restricted to late quartz and carbonate veinlets. Mo selenide, Mo telluride, galena, berthierite, and gold are very rare. Sulfur isotope results suggest the dominant source of sulfur to have been seawater sulfate, reduced by bacteria under different conditions. The delta 13 C values of the organic matter (-24.2 to -37.5ppm) reflect the combination of the carbon isotope composition of dissolved HCO 3 , its high concentration, and the type of organisms. The results of Rock-Eval pyrolysis as well as laser Raman spectroscopy show a high maturity, close to that of well-crystallized graphite. Fluid inclusion and stable isotope data from quartz and carbonate veinlets of very low grade regionally metamorphosed metalrich black shales at Kamenec and highly metamorphosed facies at Hromnice indicate that they resulted from the interaction between 18 O-rich fluids, volcanics, and metasediments. The interaction could have occurred during subsea-floor or later regional metamorphism.