On the Relationship between Refractive Index and Density for SiO2-polymorphs

Five different refraction formulas were applied to SiO₂ polymorphs in order to determine the most suitable refractive index-density relation. 13 SiO₂ polymorphs with topological different tetrahedral frameworks are used in this study including eight new low density SiO₂ polymorphs — so called “guest free porosils”. These SiO₂ polymorphs cover a density range from 1.76 to 2.92 g/cm³. The mean refractive indices (ovn) of the porosils have been determined by the immersion method, the densities (ρ) were calculated from the unit cell parameters. Assuming the polarizability (α) of all SiO₂ polymorphs to be constant the general refractivity formula $$\{ 2\overline {11} 0\} \langle 0001\rangle $$ turned out to be the most suitable for SiO₂ polymorphs. Regression analysis yields an electronic overlap parameter b=1.2(1).     

Infrared vibrational spectra of Beta-Phase Mg2SiO4 and Co2SiO4 to Pressures of 27 GPa

Infrared absorption spectra of the high-pressure polymorphs β-Mg₂SiO₄ and β-Co₂SiO₄ have been measured between 0 and 27 GPa at room temperature. Grüneisen parameters determined for 11 modes of β-Mg₂SiO₄ (frequencies of 300 to 1,050 cm^?1) and 5 modes of β-Co₂SiO₄ (490 to 1,050 cm^?1) range between 0.8 and 1.9. Averaging the mid-infrared spectroscopic data for β-Mg₂SiO₄ yields an average Grüneisen parameter of 1.3 (±0.1), in good agreement with the high-temperature thermodynamic value of 1.35. Similarly, we find a value of 1.05 (±0.2) for the average spectroscopic Grüneisen parameter of β-Co₂SiO₄.     

Intrinsic oxygen Fugacity measurements on chromites from the Bushveld Complex and their petrogenetic significance

Oxygen Fugacity measurements were carried out on chromites from the Eastern Bushveld Complex (Maandagshoek) and are compared with former measurements on chromites from the western Bushveld Complex (Zwartkop Chrome Mine). These results together with those of Hill and Roeder (1974) yield the following conditions of formation for the massive chromitite layers: Western Bushveld Complex (Zwartkop Chrome Mine) $$\begin{gathered} Layer{\text{ }}T(^\circ C) p_{O_2 } (atm) \hfill \\ LG3{\text{ 1160}} - {\text{1234 10}}^{ - {\text{5}}} - 10^{ - 7.6} \hfill \\ LG4{\text{ 1175}} - {\text{1200 10}}^{ - 6.35} - 10^{ - 7.20} \hfill \\ LG6{\text{ 1162}} - {\text{1207 10}}^{ - 6.20} - 10^{ - 7.50} \hfill \\ \hfill \\ \end{gathered} $$ Eastern Bushveld Complex (Farm Maandagshoek) $$\begin{gathered} {\text{LXI 1115}} - {\text{1150 10}}^{ - 7.80} - 10^{ - 8.80} \hfill \\ ( = {\text{Steelpoort Seam)}} \hfill \\ {\text{LX 1125 10}}^{ - 8.25} \hfill \\ {\text{V 1120 10}}^{ - 8.55} \hfill \\ {\text{LII 1120 10}}^{ - 8.0} - 10^{ - 8.60} \hfill \\ \end{gathered} $$ The comparison of the data shows, that the chronitite layers within each particular sequence were formed under approximately identicalp _{o 2}- andT-conditions. The chromites from the western Bushveld Complex, however, were formed at higher temperatures and higher oxygen fugacities than the chromites from the eastern Bushveld Complex. Fromp _{o 2}-T-curves of disseminated chromites and the temperatures derived above, the following conditions of formation for the host rocks were obtained: Western Bushveld Complex $$T = 1200^\circ {\text{C; }}p_{{\text{o}}_{\text{2}} } = 10^{ - 7.25} - 10^{ - 7.50} $$ Eastern Bushveld Complex $$T = 1125^\circ {\text{C; }}p_{{\text{o}}_{\text{2}} } = 10^{ - 8.50} - 10^{ - 9.25} $$ Consequently, the host rocks in the Zwartkop-Chrome-Mine, were formed under higher temperatures and higher oxygen fugacities than the host rocks at Maandagshoek. The rock sequence in the Zwartkop-Chrome-Mine therefore originated in an earlier stage of the differentiation of the Bushveld magma. Comparison of the chromites from the host rocks with the chromites from massive layers supports Ulmer's (1969) thesis that an increase of the oxygen fugacity is responsible for the formation of massive chromitite layers. The values in this investigation show that increases of only about 0.5–1.0 log units are necessary to enhance chromitite layer formation.     

Moho structure of Central America based on three-dimensional lithospheric density modelling of satellite-derived gravity data

The Central American isthmus hosts a highly variable Moho structure due to the diverse origin and composition of the crustal basement and the influence of large-scale neotectonic processes. Gravity data from the combined geopotential model EGM2008 were interpreted via forward modelling to outline the three-dimensional lithospheric density structure along the Middle American Trench, as well as the segmentation of the oceanic Cocos and Nazca plates and the overriding Caribbean plate. In this work, results for the depth of the Moho obtained from the density model are presented. The Quaternary volcanic arc correlates with a maximum Moho depth of 44 km in western Guatemala. To the south-east of the continental shelf, the Caribbean plate shows Moho depths between 20 and 12 km whereas to the north, values as shallow as 8 km are observed at the Cayman trough. For the oceanic Cocos plate, depths between 16 and 21 km are obtained for the Moho along the Cocos ridge, contrasting with values between 15 and 12 km for the seamount segment and 8 and 11 km for the segments of the crust that are not affected by the Galapagos hot-spot track.     

Manganese deposits in northeastern European Russia and the Urals: Isotope geochemistry,genesis, and evolution of ore formation

Based on new data on the lithology, mineralogy, chemistry, and isotopic composition of manganese carbonate ores and rocks at the deposits and occurrences in the Novaya Zemlya Archipelago, the Pai-Khoi, and the Urals, as well as using data from the literature, the main Phanerozoic basins of manganese deposition have been established in the geological history of Laurasia, Pangea, and Siberian paleocontinents. The formation conditions of manganese ore gradually changed from hydrothermal-sedimentary in the Middle Paleozoic to sedimentary-diagenetic in Mesozoic and Cenozoic. The ore was also formed under catagenetic conditions. Carbon of oxidized organic matter plays a substantial role in the formation of manganese carbonates.     

Levels and distributions of polycyclic aromatic hydrocarbons (PAHs) in middle reach of Huaihe River,China: anthropogenic influences and ecological risks

Polycyclic aromatic hydrocarbons (PAHs) are a group of aromatic hydrocarbons with high toxicity to human health. PAH emissions from industrial activities have become the primary sources of PAH contamination in Chinese watersheds. Here, we analyzed 10 individual priority PAHs in 120 water samples taken from middle reach of Huaihe River, China. The results show that the PAH levels in studied watershed are significantly lower as compared to other Chinese watersheds, approaching or slightly exceeding the PAH levels in watersheds from selected European and North American countries. We observe rather large variation in spatial and vertical PAH distributions, pointing to PAH inputs from local industrial emissions, and PAH cycle among atmosphere, water and sediment. Individual PAH ratios (i.e., phenanthrene/anthracene and fluorene/pyrene) and principal components analysis suggest a primarily pyrolytic PAH sources (combustion of coal and coke) in water column. Other accompanying PAH sources include emissions from steel industry and gasoline. Total toxic benzo[a]pyrene equivalent of PAHs in studied water column indicates that PAHs in watershed of middle reach of Huaihe River pose limited toxicity to the environment.     

The structural role of Al2O3 and TiO2 in immiscible silicate liquids in the system SiO2-MgO-CaO-FeO-TiO2-Al2O3

The effects of the addition of Al₂O₃ on the large stable two liquid field in the SiO₂-TiO₂-CaO-MgO-FeO system were experimentally determined. The increase of Al₂O₃ content in the starting composition results in the decrease of critical temperature, phase separation and liquidus temperature of the two liquid field until it is rendered completely metastable. The shrinkage of the two liquid field indicates that Al₂O₃ is acting in the role of a network former and homogenizes the structure of the two melts. In this alkali-free system Al⁺³ utilizes the divalent cations, Ca⁺² and Mg⁺², for local charge balance with a preference for Ca⁺² over Mg⁺². Thus, AlO₄ tetrahedra combine with SiO₄ tetrahedra to form an aluminosilicate framework which polymerizes the SiO₂-poor melt and makes it structurally more similar to the SiO₂-rich melt. However, Ca⁺² and Mg⁺² are not as efficient in a charge balancing capacity as the monovalent K⁺ and Na⁺ cations. The lack of alkalis in this system limits the stability of AlO₄ tetrahedra in the highly polymerized SiO₂-rich melt and results in the preference of Al₂O₃ for the SiO₂-poor melt. The partitioning systematics of Ti are virtually identical to those of Al. It is concluded that Ti occurs in tetrahedral coordination as a network forming species in both the high — and low — SiO immiscible melts.     

Phylogenetic Problems in Polynesian Simuliidae (Diptera: Culicomorpha): A progress report

As a basis for eventual control of the vicious anthropophilic and ornithophilic simuliid females of the Marquesas Islands, a taxonomic revision of Polynesian Simuliidae is in progress. Cytotaxonomic studies reveal two simuliid species in Rarotonga, Cook Islands; nine species in Tahiti, Society Islands, and two in the Marquesas Islands. A cytophylogeny is now available. Polynesian Simuliidae are unique in possessing heterogametic females. A reconstructed phylogeny, based mainly on morphological character states of larvae and pupae, agrees well with the cytophylogeny. One of the new species which is closely related to Simulium oviceps Edwards has larvae with highly reduced, non-functional cephalic fans. Ages of the Polynesian islands are discussed in relation to possible dispersal of Simuliidae into Polynesia.     

Effects of pH on isotherm modeling and cation competition for Cd(II) and Cu(II) biosorption on Myriophyllum spicatum from aqueous solutions

The biosorption characteristics of Cd(II) and Cu(II) ions from aqueous solutions obtained using submerged aquatic plant (Myriophyllum spicatum) biomass were investigated in terms of equilibrium, kinetics, thermodynamics, and cation competition. Langmuir and Freundlich models were applied to describe the biosorption isotherm of metal ions by M. spicatum biomass and isotherm constants considering the most important parameter, pH. The variation of sorption isotherm constants showed pH dependence. The Langmuir and Freundlich models fitted the equilibrium data well. The maximum biosorption capacity (q _m) of M. spicatum biomass was determined to be 29.07 mg/g for the Cd(II) ion at pH 5.0 and 12.12 mg/g for the Cu(II) ion at pH 6.0. Chi square analysis showed that the Freundlich model fitted the equilibrium data better than the Langmuir isotherm. Competition of Cd(II) and Cu(II) in a binary solution showed that the Langmuir monolayer capacity of Cd(II) decreased from 29.07 mg/g with only Cd(II) in solution to 12.02 mg/g in the presence of Cu(II). Kinetics results showed that the biosorption processes of both metal ions followed the pseudo-second-order kinetics well. The calculated thermodynamic parameters (?G ⁰, ?H ⁰, and ?S ⁰) showed that biosorption of Cd(II) and Cu(II) ions onto M. spicatum biomass was feasible, spontaneous, and endothermic in nature. Fourier transform infrared spectroscopy spectrum analysis revealed that Cd(II) and Cu(II) sorption was mainly ascribed to carboxyl, hydroxyl, amine, and C–N groups in M. spicatum.     

Avian cholera and organochlorine residues in an American oystercatcher

Pasteurella multocida, the causative bacterium of avian cholera, was isolated from cultures of the liver and heart blood of a female, adult American oystercatcher (Haematopus palliatus) found dead on the Cape Romain National Wildlife Refuge, South Carolina, in May 1973. This is apparently the first record of avian cholera in the oystercatcher. Low levels of DDE were identified in tissues of the oystercatcher.     

Electrical conductivity measurements on olivines and pyroxenes under defined thermodynamic activities as a function of temperature and pressure

Electrical conductivities of Ni₂SiO₄, Fe₂SiO₄, and MgSiO₃ were measured on synthetic powders in the temperature range 340° to 1,100° C and at pressures up to 20 kbars. For ternary compounds such as olivines and pyroxenes the control of two further variables, like the chemical activities of two components are needed, besides temperature and pressure. The activities of the corresponding binary oxides were controlled by equilibrating the samples with their neighbour-phases. Control of the oxygen partial pressure was achieved by buffer techniques. From the slopes of the lg σ vs. 1/T lines the activation energies were calculated for 10 kbar: 0.56 eV and 2.7 eV for Ni₂SiO₄ in equilibrium with SiO₂ and Ni/NiO-buffer for the temperature range 500°–800°C and 800°–1,000°C resp. 0.52 eV for Fe₂SiO₄ in equilibrium with SiO₂ and metallic iron, and 0.38 eV in equilibrium with SiO₂ and magnetite; 1.11 eV for MgSiO₃ in equilibrium with SiO₂, and 1.25 eV in equilibrium with Mg₂SiO₄.     

Polycyclic aromatic hydrocarbons in surface sediments of Binacional Itaipu Lake,Brazil: characteristics,sources and toxicity evaluation

Itaipu Lake, which includes the Itaipu hydroelectric power plant, is one of the largest dams in the world and has a strong relationship with its surroundings. The flooded area has multiple uses such as navigation, recreation, water abstraction for industrial, urban and agricultural irrigation. The lake is located at the frontier between Brazil, Argentina and Paraguay. In this study, superficial sediments collected from nine sampling sites were analysed for grain size, organic matter and 16 priority polycyclic aromatic hydrocarbons (PAHs) using high-performance liquid chromatography (HPLC) with fluorescence detector. The total concentration of PAHs in the dry sediment ranged from 35.21 to 685.37 µg kg^?1. Diagnostic ratios showed that the possible source of PAHs in the Itaipu Lake could be pyrolitic and petrogenic. The potential toxicity of sediment of PAHs varied from not detected to 127.70 µg g^?1, suggesting that some adverse ecological effects would arise due to PAHs in these sediments.     

Infrared spectra of olivine polymorphs: α, β phase and spinel

Infrared (IR) absorption spectra are presented for olivine (α) and spinel (γ) phases of A₂SiO₄ (A=Fe, Ni, Co) and Mg₂GeO₄. IR spectra of β phase (“modified spinel”) Co₂SiO₄ and of α Mg₂SiO₄ are also included. These results provide reference spectra for the identification of olivine high-pressure polymorphs. Isostructural and isochemical correlations are used to support a general interpretation of the spectra and to predict the spectrum of γ Mg₂SiO₄. A γ Mg₂GeO₄ sample equilibrated at 1,000° C shows evidence of partial inversion, but one equilibrated at 730° C does not. This suggests that partial inversion could occur in silicate spinels at elevated temperatures and pressures, however no evidence of inversion is seen in the ir spectra of the silicates in this study.     

Study of pocyclic aromatic hydrocarbons at a pressure of 6–9 GPa with X-ray diffraction and synchrotron radiation

This work is one of the stages of study of the deep C-O-H fluid and investigates the behavior of polycyclic aromatic hydrocarbons (PAHs) under conditions of the Earth’s mantle. The composition of the C-O-H fluid in the upper mantle is estimated as a mixture of H₂O and CH₄ with a minor amount of H₂ and heavier hydrocarbons. Some theoretical calculations show that the stability of heavy hydrocarbons (alkanes, alkenes, and PAHs) increases with an increase in temperature. This paper presents the results of an XRD study of PAHs stability in multianvil presses on a Spring-8 accelerator (Japan). The primary compositions were chosen according to the abundance of PAHs in nature. In situ diffraction spectrums were recorded to determine the PAHs stability field. It was established that the PAHs become unstable at a pressure of 6–9 GPa and a temperature of 873–1073 K.     

Clicking graphene oxide and Fe3O4 nanoparticles together: an efficient adsorbent to remove dyes from aqueous solutions

Nanohybrid of graphene oxide (GO) and azide-modified Fe₃O₄ nanoparticles (NPs) were fabricated using click reaction. First, Fe₃O₄ NPs were modified by 3-azidopropionic acid. Then, click-coupling of azide-modified Fe₃O₄ NPs with alkyne-functionalized GO was carried out in the presence of CuSO₄·5H₂O and sodium l-ascorbate at room temperature. The attachment of Fe₃O₄ NPs onto the graphene nanosheets was confirmed by Fourier-transform infrared (FTIR) spectroscopy, scanning electron microscopy, thermogravimetric analysis, energy dispersive X-ray spectrometry and X-ray diffraction spectrometry. As the FTIR spectroscopy and energy dispersive X-ray spectrometry analysis showed, the final magnetic graphene nanosheets were also reduced by sodium ascorbate which is a merit for click-coupling reactions. The specific saturation magnetization of the Fe₃O₄-clicked GO was 44.3 emu g^?1. The synthesized hybrid was used in the adsorption of methylene blue and congo red (CR). The adsorption capacities in the studied concentration range were 109.5 and 98.8 mg g^?1 for methylene blue and CR, respectively.     

Clinopyroxene on the join CaMgSi2O6-CaFe3+AlSiO6-CaTiAl2O6 at low oxygen fugacity

Subsolidus phase relations on the join CaMgSi₂O₆-CaFe³⁺ AlSiO₆-CaTiAl₂O₆ were studied by the ordinary quenching method at \(f_{O_2 } = 10^{ - 11} \) atm and 1,100°C. Crystalline phases encountered are clinopyroxene_ss (ss:solid solution) (Cpx_ss), melilite (Mel), perovskite (Pv), spinel_ss (Sp_ss), magnetite_ss (Mt_ss) and anorthite (An). There is no Cpx_ss single phase field, and the following assemblages were found; Cpx_ss+Mel, Cpx_ss+Mel+Sp_ss, Cpx_ss+Mel+Pv, Cpx_ss+Mel+Sp_ss+Pv, Cpx_ss+Pv+Sp_ss+An, Sp_ss+Pv+Mel+An+Cpx_ss, Mel+Mt_ss+An+Sp_ss+Cpx_ss+liquid and Mel+Mt_ss+An+Sp_ss+Cpx_ss+Pv. Mössbauer spectral study revealed that Cpx_ss contains both Fe²⁺ and Fe³⁺ in the octahedral site, and it was confirmed that the CaFe³⁺ AlSiO₆ content in the Cpx_ss at low \(f_{O_2 } \) is considerably less than that in the Cpx_ss crystallized in air, whereas the CaFe²⁺Si₂O₆ component increases. The maximum solubility of CaTlAl₂O₆ component in the Cpx_ss at low \(f_{O_2 } \) is higher than that in air. The decrease of CaFe³⁺ AlSiO₆ in the Cpx_ss at low \(f_{O_2 } \) may cause increase of CaTial₂O₆ in the Cpx_ss.     

Structural setting and genesis of ore bodies in carbonate rocks in the M.te Atzei-M.te Ega mining area (Sulcis,SW Sardinia)

At least seven different types of ore bodies, with an ore stock of Ba, F, Fe, Pb, Zn, Cu and Sb occur in Paleozoic rocks (Lower-Middle Cambrian and Ordovician) in an ?15 km² area north of the Narcao village (SW Sardinia, Italy). The ore bodies are related both to syngenetic accumulations, and later epigenetic recirculation of the primary ores. In the Lower Cambrian the area studied shows evidence of synsedimentary tectonic instability, probably related to carbonate shelf margin features. The Upper Cambrian is lacking and the transgressive Ordovician sediments cover large areas of the previously gently folded Cambrian rocks (Sardic phase of Caledonian orogenesis). The main Hercynian tectonic phases had a much stronger compressive folding that is mirrored in a sequence of tight folds and upthrusts. The geometric setting resulting from the tectonic frame of the Cambrian and Ordovician sediments must be taken into account to understand the distribution and the genesis of most of the ore bodies.     

Origin and composition of the ferruginous oolites and laterites of North-Western Nigeria

The ferruginous deposits of north-western Nigeria occur extensively capping sediments which outcrop over thousands of square kilometers. These deposits could be subdivided into 3 major groups:

1. Ferruginous oolites;
2. Crusty/Concretionary laterites;
3. Ferruginous sandstones.

The iron-rich oolites are primary deposits and deposition of ferruginous materials occurred during the late Paleocene. All gradations can be traced between a pure oolitic ironstone and concretionary laterite with scattered oolitic grains of limonite. The crusty laterites and Ferruginous sandstone were formed during the late Tertiary or early Quaternary. They are definitely post Miocene in age and consists of abundant angular quartz grains embedded in a matrix of gothite, haematite, limonite and clay. The laterites and oolites posses different element concentrations which indicate formation under different environmental conditions ranging from deep Marine through shallow near shore marine to continental (fluviatile and lacustrine). The crusty laterites and ferruginous sandstones in northwestern Nigeria attain a thickness of approximately 4 meters or more forming the crust of flat-topped hills or mesas. They are almost certainly equivalent to the laterites covering much of the Northern plains and the Fluvio-volcanic series of the Jos Plateau. In northwestern Nigeria the laterites are restricted to outcrops of sediments of appropriate composition and drainage properties. These ferruginous deposits are usually massive with almost horizontal bedding planes marked by abrupt or gradual changes in morphology and lithology. Cross bedding and ripple-marks can be observed at Gundumi and Imasa as well as in Birnin Kebbi and large scale stratification of the laterites occur at Kalambaina. Laminations are generally localised.     

Factors effecting the stability field of Ca-poor pyroxene and the origin of the Ca-poor minimum in Ca-rich pyroxenes from tholeiitic intrusions

Ca-poor pyroxene ceases to crystallise towards the end of fractionation in tholeiitic intrusions and is usually replaced by Fe-rich olivine. Using the data of Nicholls et al. (1971), the \(a_{{\text{SiO}}_2 }\) at which olivine and pyroxene can coexist has been calculated at different temperatures and pressures. From these calculations it is clear that the Fe/Mg ratio of the last Ca-poor pyroxene to crystallise from a melt is increased by raising the temperature or pressure of crystallisation. The Ca-poor pyroxene-Fe-rich olivine relationship is also dependent on the \(a_{{\text{SiO}}_2 }\) of the melt. In magmas which crystallise Fe-rich olivine before quartz, inicreasing their \(a_{{\text{SiO}}_2 }\) will raise the Fe/Mg ratio of the last Ca-poor pyroxene to crystallise. If the \(a_{{\text{SiO}}_2 }\) of the magma is so high that SiO₂ saturation is reached before the appearance of cumulus Fe-rich olivine, any further increase in the \(a_{{\text{SiO}}_2 }\) of the melt will not influence the stability field of Ca-poor pyroxene. The replacement of Ca-poor pyroxene by Fe-rich olivine requires the magma to reach a high level of a _FeO late in its fractionation. If a magma fractionates with an FeO depletion trend, Ca-poor pyroxene is replaced by Ca-rich pyroxene. The reaction is initiated by the appearance of cumulus K-feldspar which results in a marked reduction in the amount of anorthite crystallising from the magma. This increases the a _CaO of the melt so that Ca-poor pyroxene is replaced by Ca-rich pyroxene.     

Some physical properties of amorphous SiO2 synthesized by shock compression of α quartz

The amorphous phase of SiO₂ produced upon recovery of shock-compressed quartz demonstrates a wide range of refractive indices which can be correlated to the shock state. Both infra-red absorption spectra and X-ray diffraction patterns indicate that the shock-produced amorphous SiO₂ has a statistically more-random atomic distribution and longer Si-O and shorter Si-Si separation than does fused silica. By accounting for phase transformation, the calculated values of the shock and residual temperature are much higher than those obtained by Wackerle (1962) to a pressure of 700 kbar. Our results are consistent with experimental ones.