Showing papers on "Silicate minerals published in 2003"

Identification and evolution of hydrogeochemical processes in the groundwater environment in an area of the Palar and Cheyyar River Basins, Southern India

Abstract: The Palar and Cheyyar River Basins in Tamil Nadu state of Southern India are characterised by different geological formations, and groundwater is the major source for domestic, agricultural and other water-related activities. Hydrogeochemical studies were carried out in this area with the objective of identifying the geochemical processes and their relation to groundwater quality. Groundwater samples were collected once a month from 43 groundwater wells in this area from January 1998 to July 1999. Sampling procedures and chemical analysis were carried out as per the standard methods. Chemical data are used for mathematical calculations and graphical plots to understand the chemical process and its relation to the groundwater quality. The chemical composition of groundwater in the central part of the study area mainly depends on the recharge from lakes and the river, which is explained by a mixing mechanism. In addition, weathering of silicate minerals controls the concentration of major ions such as sodium, calcium, magnesium and potassium in the groundwater of this area. Further, the activity ratios indicate that the groundwater is in equilibrium with kaolinite, smectite and montmorrillonite. The reverse ion exchange process controls the concentration of calcium, magnesium and sodium in hard rock formations, and dissolution of carbonate minerals and accessory minerals is the source of Ca and Mg, in addition to cation exchange in the sedimentary formations. In general, the chemical composition of the groundwater in this area is influenced by rock–water interaction, dissolution and deposition of carbonate and silicate minerals, ion exchange, and surface water interactions.

Study of low rank greek coals using FTIR spectroscopy

Abstract: Fourier transform infrared (FTIR) spectra of lignite and humic clay samples, collected from 2 boreholes located at Apofysis-Amynteo lignite deposit, NW Greece, as well as their insoluble organic matter, obtained by Soxhlet extraction with dichloromethane, were recorded between 400 and 4,800 cm−1. In the same way, FTIR spectroscopy was used to study a xylite sample from Vevi xylite basin (north of Apofysis-Amynteo lignite deposit) and its chars, which are the solid products of pyrolysis, at 3 final fixed temperatures: 400°C, 600°C, and 800°C. In the Apofysis-Amynteo samples, oxygen-containing structures were observed in the 1,800–1,000 cm−1 zone, aliphatic hydrogen in the 2,950–2,700 cm−1 zone, aromatic out-of-plane structures in the 900–670 cm−1 zone, and hydroxyl groups in the 3,400–3,600 cm−1 zone. A great abundance of C=O and C–O–R structures in the 1,800–1,000 cm−1 region were noticed, while clay and silicate minerals were identified in the 400–600 cm−1 and 3,600–3,800 cm−1 zones. In the IR spectra of...

Bromine in scapolite-group minerals and sodalite: xrf microprobe analysis, exchange experiments, and application to skarn deposits

Abstract: Application of an X-ray fluorescence (XRF) microprobe for the analysis of single grains (80 to 1,000 μm in diameter) of Cl-rich minerals for Br has been evaluated for fluorapatite, chlorapatite, scapolite-group minerals (marialite and meonite) and sodalite. A calibration curve based on the Br contents in four international reference materials has been confirmed by measurements on Br-bearing standard solutions and by agreement with the results of Cl-rich minerals from instrumental neutron-activation analyses. Absolute errors associated with individual XRF microprobe analyses ( i.e ., counting statistics alone) are less than 5%, and the calculated limit of detection in the analysis of single mineral grains is ~1 ppm Br. Matrix and grain-size effects are shown to be negligible. Experiments at 1 atmosphere and 800 to 1000°C yield the following distribution coefficients for Br–Cl exchanges between marialite or sodalite and hydrous NaCl–NaBr melts: KDmarialite–melt = 0.97 ± 0.08 and KDsodalite–melt = 0.9 ± 0.1. Therefore, the Cl/Br values in marialite and sodalite closely reflect the halogen proportions of their coexisting melts or fluids. The diffusivity of Br in sodalite follows an Arrhenius relation: DBr = 6.5 × 10−7 exp(−270 ± 10kJ/mol/RT) m2/s, over the temperature range from 800 to 1000°C. DBr in marialite is 1.7 ± 0.3 × 10−19 m2/s at 800°C. The Cl/Br weight ratios of marialite in the Tieshan Fe skarn deposit, China, cluster around 650 ± 40, supporting an origin involving hydrothermal brines from associated evaporites. Scapolite-group minerals in the exoskarns of the Nickel Plate Au skarn deposit, British Columbia, have Cl/Br from 560 to 570, higher than those (130 to 180) of their counterparts in the endoskarns and vuggy cavities. This variation is attributable to an increased involvement of magmatic water from distal to proximal zones. Similarly, scapolite-group minerals in the Grenville U–Th–Mo REE pegmatite–skarn–vein deposits vary widely in Cl/Br, from 80 to 380, indicative of mixed sources of hydrothermal fluids. This study shows the potential of Br analysis of Cl-rich silicate minerals for constraining the sources and evolution of hydrothermal fluids.

Carbonate verse silicate Sr isotope in lake sediments and its response to Little Ice Age

Abstract: The87Sr/86Sr ratios of silicate (acid-insoluble, AI) and carbonate (acid-soluble, AS) of the lake sediments from the Daihai Lake, Inner Mongolia, since the last 500 years are measured respectively, indicating that chemical weathering of silicate minerals was in an early stage since the Little Ice Age within the Daihai watershed by combination with mineral constitute, Rb/Sr ratio and CaCO3 content in the sediments. During the Little Ice Age maximum, an evident peak in the87Sr/86Sr ratios of both silicate and carbonate in sediments suggests that a cold climate condition is unfavorable to dissolving radiogenic strontium from silicate minerals. Meanwhile, the variation of87Sr/86Sr ratios of silicate and carbonate also reflects a projected warming climate favorable to intensifying chemical weathering after the Little Ice Age. Consequently, the87Sr/86Sr ratio of both silicate and carbonate in inland lake sediments can be used as an effective proxy of the past climate in single watershed.

Retrograde mineral reactions in saline fluid inclusions: The transformation ferropyrosmalite ↔ clinopyroxene

Abstract: Evidence is presented for retrograde reaction of silicate minerals with saline brine inside fluid inclusions during post-entrapment cooling. Ferropyrosmalite [(Fe,Mn)8Si6O15(OH,Cl)10, where Fe>>Mn] has previously been interpreted as a daughter mineral in saline inclusions in magmatic quartz from altered granodiorite associated with the Vyhne-Klokoc Fe-skarn deposit of Slovakia. Based on combined Raman spectroscopic, microthermometric, and SEM-EDX techniques this phase is shown to react, on heating above 450 °C with a Ca-enriched saline inclusion fluid, to form clinopyroxene. This suggests that clinopyroxene was originally present in the inclusions at high temperature, and then underwent retrograde reaction with the saline fluid, on cooling, to form ferropyrosmalite. In its simplest form, the equilibrium reaction for this transformation is: ![Formula][1] In practice, the reaction is complicated by the presence of Mn and Mg. The resulting “daughter” mineral assemblage observed at room temperature is actually a low-temperature equilibrium assemblage very different to that originally present at high temperature. Although silicate daughter minerals such as clinopyroxene are rarely, if ever, described in fluid inclusions, they may have originally been present but underwent similar retrograde reactions. Ferropyrosmalite itself is likely to be frequently overlooked, as in the absence of Raman spectroscopic analyses it may be mistaken for one of a range of possible hydrated iron-chloride minerals. Improved Raman spectra for ferropyrosmalite are presented which will make future identification easier. Failure to recognize intra-inclusion retrograde reactions such as this may lead to misinterpretation of fluid inclusion chemistry, including metal and silica solubilities. [1]: /embed/tex-math-1.gif

An assessment of nuclear microprobe analyses of B in silicate minerals

Abstract: With recent findings of substantial amounts of B in rock-forming minerals, it has become evident a need exists for microprobe techniques allowing quantitative B determinations in minerals. A microprobe method based on the nuclear reaction B-11(p,alpha)2alpha has the potential to become a powerful tool for analyses of minerals with B contents spanning a wide concentration range. In this paper, we present nuclear microprobe analyses of B in a set of silicate minerals containing stoichiometric concentrations of B in the range 1.9-8.8 wt%. Our results strongly indicate that nuclear reaction analyses of silicates utilizing the B-11(p,alpha)2alpha nuclear reaction are virtually matrix-insensitive, and saturation effects are negligible within the studied range of B concentrations. This finding suggests that it is adequate to use a single B standard for calibration purposes for analyses covering wide ranges of B concentrations in silicates. In addition, we demonstrate how B-concentration maps of high contrast and resolution may be produced by scanning the proton beam over the samples. (Less)

XPS Analysis on Adsorption Law of Metal Ion on Surface of Silicate Minerals

Abstract: Adsorption law of Cu 2+ and Pb 2+ on surface of some kinds of silicate minerals have been studied by X ray photoelectron spectrometric (XPS), and electronic binding energy and relative content varieties of mineral surface element have also been researched before and after metal ion and collector sodium oleate are adsorbed, combined with flotability varieties of silicate minerals before and after metal ions are adsorbed, adsorption law of metal ion and sodium oleate on the surface of different silicate minerals have been analyzed.

Phenocrysts in obsidian glasses

Abstract: The aim of the current paper is to map minerals mainly of Carpathian obsidian glasses by nuclear microprobe based on the particle induced X-ray emission (PIXE) providing analytical data on them for the first time. Some samples from Armenia, Greece are also involved to make a comparison with the Carpathian specimens. The following minerals are identified and analyzed: pyrrhotite, chalcopyrite, pyrite, zircon, pyroxene, biotite, plagioclase feldspar, and anhydrite. On the basis of rock-forming silicate minerals, some petrologic processes are outlined. With the identification of accessory minerals (anhydrite, pyrrhotite, chalcopyrite, pyrite), some geological conclusions are also drawn.

Proton exchange membrane fuel cell using solid electrolyte membrane of sheet silicate minerals and an intercalation compound

Abstract: A solid proton exchange membrane and a membrane-electrode assembly (MEA) for use in fabricating an inexpensive and efficient proton exchange fuel cell (PEFC) which enables direct use of an organic fuel without a reformer and use of hydrogen gas. In particular, an electrochemical cell including a solid electrolyte membrane made of one or plural kinds of layered silicate minerals or intercalation compounds. The layered silicate minerals can be easily fabricated into a solid electrolyte membrane which shows a “molecular sieve effect” on the target fuel if the density and impregnated liquid contents are properly controlled. The catalyst can be selected from a wide range of candidate materials. The use of the layered silicate mineral allows to fabricate an inexpensive direct methanol fuel cell (DMFC) and a realistic direct ethanol fuel cell (DEFC). Furthermore, an energy-efficient PEFC using hydrogen gas can also be produced therefrom.

Minerals from MacedoniaXI. Silicate varieties and their localities - Identification by FT IR Spectroscopy

Abstract: Among the rich orc deposits present in Macedonia, the silicate minerals arc thc most numerous group. The great majority of these minerals appear as rathcr large and well formed single crystal aggregates in the nature. Sometimes, however, some of the mineral species appear in association with other minerals whose crystals are not well developed. Here an overview of the basic morphological, physico-chemical and crystallographic characteristics of the most typical silicates collected from various localities within the Republic of Macedonia is given. The mineralogical and petrological features of the localities where the specimens are collected from are presented as well. Also an attempt to identify the minerals using the Ff IR spectroscopy and to classify them according to their structural characteristics is performed. The identification of the minerals was based on the comparison of the infrared spectra of our specimens with the corresponding literature data for the mineral species originating all over the world. The coloured pictures of all studied silicate minerals are presented as well.

A study of environmental analysis of urban river sediments using activation analysis

Abstract: Sediments of the Kitajukkengawa River (Sumida-ku, Tokyo, Japan) were analyzed by activation analyses Concentrations of 36 elements for each sample were determined by instrumental neutron activation analysis (INAA) and neutron induced prompt gamma-ray analysis (PGA) Based on the correlation matrix between the elements in vertical distribution, principal component analysis (PCA) was performed The degree of chemical weathering of silicate minerals was highest in the middle layer of the Kitajukkengawa River sediment and that adsorbed amount of trace metals such as Cd and Cr was increased along with chemical weathering

Acid base properties, structons and the thermodynamic properties of silicate melts

Abstract: Dept of Earth Sciences, University of Oxford, Parks Road,Oxford OX1 3PR don@earth.ox.ac.ukThe interpretation of the thermodynamic properties ofsilicate melts and slags in terms of oxide acid-base reactions(Flood and Forland 1947, Fincham & Richardson 1954) hashad widespread use in metallurgy where the thermodynamicactivities of oxide species are of primary concern. Quasi-chemical models (e.g. Toop & Samis 1962, Esin 1973) andpolymer models (e.g. Masson et al. 1970, Lahiri 1971) haveattempted to relate these thermodynamic data on oxideactivities to speciation in melts and slags.The focus of interest in the earth sciences and in the glassindustry is on the crystallization of silicate minerals fromsilicate melts and on the physical properties of the melts andglasses themselves. This requires adequate expression, not ofoxide activities, but of silicate components. The relationshipof the acid-base properties of melts to their thermodynamicproperties requires description of the acid-base reactions andof the amphoteric properties of oxide components (Fraser1975). The role of basicity in controlling the thermodynamicproperties of silicate melts has recently been revisited byBeckett (2002). Moreover, new NMR data (Xue and Kanzaki2002) show that water displays important amphotericbehaviour in molten silicates. Thus in basic melts such asCaMgSi

- Effect of Pressure, Temperature, and Aqueous Carbon Dioxide Concentration on Mineral Weathering as Applied to Geologic Storage of Carbon Dioxide

Abstract: Publisher Summary CO2 mediated dissolution of silicate minerals and subsequent precipitation of carbonates in deep saline aquifers may allow permanent trapping of carbon dioxide However, the time-scales and extents of the reactions are poorly understood for CO2 receptor formation conditions To address these shortcomings, experiments were conducted to investigate the effects of pressure, temperature, and aqueous solution composition on rates and mechanisms of silicate mineral dissolution and carbonate precipitation A high pressure/high temperature flow-through reactor system was used to derive steady-state dissolution rates of crushed forsteritic olivine The system allowed continuous monitoring of temperature, pressure, and pH, and periodic sampling of effluent fluids for dissolved ion concentration analysis Preliminary measurements of dissolution rates indicate good agreement with previously published measurements at ambient conditions Increasing the pressure from 1 to 100 bar under constant CO2 conditions increased the dissolution rate by 80% The same reactions were studied in batch systems using an array of analytical techniques to investigate dissolution mechanisms and secondary precipitate formation The extent of olivine dissolution in the batch reactors increased with temperature, PCO2 and surface area Precipitation of magnesium-rich carbonates on reacted olivine was observed at initial magnesite saturation indices greater than 16

Zeolite Formation and Weathering Processes Within the Martian Regolith: An Antarctic Analog

Abstract: As more information is obtained about the nature of the surface compositions and processes operating on Mars, it is clear that significant erosional and depositional features are present on the surface. Apparent aqueous or other fluid activity on Mars has produced many of the erosional and outflow features observed. Evidence of aqueous activity on Mars has been reported by earlier studies. Gooding and colleagues championed the cause of pre-terrestrial aqueous alteration processes recorded in Martian meteorites. Oxygen isotope studies on Martian meteorites by Karlsson et al. and Romenek et al. gave evidence for two separate water reservoirs on Mars. The oxygen isotopic compositions of the host silicate minerals was different from the oxygen isotopic composition of the secondary alteration products within the SNC meteorites. This implied that the oxygen associated with fluids which produced the secondary alteration was from volatiles which were possibly added to the planetary inventory after formation of the primary silicates from which the SNC s were formed. The source of the oxygen may have been from a cometary or volatile-rich veneer added to the planet in its first 600 million years.

A New Type of Stardust

Abstract: Many meteorites contain small quantities of microscopic particles with unusual mixes of isotopes. The abundances of the isotopes, such as the relative amounts of oxygen-16, 17, and 18, indicate an origin outside the solar system. The dust particles are bits of stars, some of which no longer exist. Since their discovery in the late 1980s, only grains made of carbon (diamond and graphite), carbides, and oxides have been found. None were silicates--compounds that contain silicon, oxygen, and assorted other ions such as magnesium and calcium. This seemed peculiar to scientists because meteorites and the rocky planets are made mostly of silicate minerals. Part of the problem might have been a sampling bias introduced by the way grains of stardust were extracted, which involves dissolution of meteorites by strong acids. Silicates are more easily dissolved than carbides, oxides, or carbon compounds. However, Scott Messenger and his colleagues at Washington University in St. Louis and at the Johnson Space Center in Houston have found silicate grains in interplanetary dust particles, which are probably remnants of comets. This shows that presolar silicates exist, but it leaves open the question of why none have been found in meteorites.

MöSsbauer Spectroscopy in Studying the Thermally Induced Oxidation of Fe2+ Cations in Iron-Bearing Silicate Minerals

Abstract: The oxidation mechanisms of Fe2+ in different iron-bearing minerals depend strongly on the external conditions, including the heating temperature, mineral crystal unity, pressure conditions and oxidation atmosphere. However, slight differences in the internal features (the total content of iron, distribution of iron in non-equivalent sites, chemical environment and coordination of iron) can also significantly influence the oxidation mechanism. Thus, different oxidation routes can occur depending on the structural ordering and external conditions.