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Showing papers on "Silicate minerals published in 1991"


Journal ArticleDOI
TL;DR: In this article, the authors used published data relevant to the geochemistry of vanadium to evaluate processes and conditions that control vanadium accumulation in carbonaceous rocks, including reduction, adsorption, and complexation of dissolved vanadium.

377 citations


Journal ArticleDOI
TL;DR: In this article, the influence of ferric estimates on T and P calculations depends on the model used and on the extent the ferric estimate alters the relative proportions of end-members.
Abstract: The ferromagnesian silicate minerals, such as garnets, pyroxenes, micas, and amphiboles, appear in a variety of geothermometers and geobarometers. Where complete chemical analyses are available and regardless of bulk composition (metamorphosed pelitic or mafic), the aforementioned minerals commonly contain ferric iron. In mineral analyses using the electron microprobe, ferric and ferrous iron are not distinguished, and all the iron is treated as FeO. In ferric Fe-bearing minerals, this treatment results in (1) low analytical sums and (2) excess cations in the mineral formulae. Assuming ideal stoichiometry (ideal formula cations and oxygens) allows direct ferric estimates in garnets and pyroxenes; amphiboles require additional assumptions concerning site occupancies, and, for micas, no acceptable constraint exists for a ferric estimate. Based on ferric iron determinations for some metamorphic ferromagnesian silicates, the proportion of ferric to total iron increases at higher Xug values. The influence of ferric estimates on T and P calculations depends on the model used and on the extent the ferric estimate alters the relative proportions of end-members. Several examples suggest that, in general, if ferric estimates (or determinations) are made, they should be made for all the relevant minerals.

120 citations


Journal ArticleDOI
01 Mar 1991
TL;DR: In this article, the rate of capillary rise of a liquid in a powder is related to the contact angle between the liquid and the solid by the Washburn equation, and the contact angles were used to determine the apolar (Lifshitzvan der Waals) component of the total interfacial surface energy using the Young equation.
Abstract: The components of the interfacial surface tension of talc and pyrophyllite were determined by measuring the rate of the capillary rise of a number of liquids through thin, sedimented deposits of the powdered minerals. The rate of capillary rise of a liquid in a powder is related to the contact angle between the liquid and the solid by the Washburn equation. The contact angles thus derived were used to determine the apolar (Lifshitzvan der Waals) component, γ LW , and the polar, electronacceptor and electron-donor parameters, γ ⊕ and γ ⊖ respectively, of the Lewis acid/base component of the total interfacial surface energy using the Young equation. The values of γ LW for talc and pyrophyllite (31.5 and 34.4 mJ/m2) are slightly smaller than for smectite clay minerals (e.g., the value for hectorite is 39.9 mJ/m2), the electron donor parameter values are roughly comparable for talc and pyrophyllite (γ ⊕ = 2.4 and 1.7 mJ/m2) as are the values of the electron acceptor parameter (γ ⊖ = 2.7 and 3.2 mJ/m2). The well-known hydrophobicity of these two minerals is due to the remarkably small value (for silicate minerals) of γ ⊖(γ⊕ is normally small or zero for silicates and many other oxides). The small values of both γ ⊕ and γ ⊖ mean that the Lewis acid/base interactions between talc or pyrophyllite and highly polar water molecules are very weak. In contrast, low-charge smectites, the minerals most similar chemically and structurally to talc and pyrophyllite, have much greater values of γ ⊖ (≥ 30 mJ/m2) and are hydrophyllic.

109 citations


Journal ArticleDOI
01 Apr 1991-Geology
TL;DR: In this paper, an investigation of silicate weathering in a Minnesota mire indicates that quartz and aluminosilicates rapidly dissolve in anoxic, organic-rich, neutral- pH environments.
Abstract: An investigation of silicate weathering in a Minnesota mire indicates that quartz and aluminosilicates rapidly dissolve in anoxic, organic-rich, neutral- pH environments. Vertical profiles of pH, dissolved silicon, and major cations were obtained at a raised bog and a spring fen and compared. Profiles of readily extractable silicon, diatom abundance, ash mineralogy, and silicate surface texture were determined from peat cores collected at each site. In the bog, normally a recharge mound, dissolved silicon increases with depth as pH increases, exceeding the background silicon concentration by a factor of two. Silicate grain surfaces, including quartz, are chemically etched at this location, despite being in contact with pore water at neutral pH with dissolved silicon well above the equilibrium solubility of quartz. The increasing silica concentrations at circum-neutral pH are consistent with a system where silicate solubility is influenced by silica-organic-acid complexes. Silica-organic-acid complexes therefore may be the cause of the almost complete absence of diatoms in decomposed peat and contribute to the formation of silica-depleted underclays commonly found beneath coal.

91 citations


Journal ArticleDOI
TL;DR: In this paper, the main minerals in the coal are quartz, pyrite, and a clay fraction consisting of kaolinite, illite and an expandable, irregular mixed-layer mineral.

86 citations


Journal ArticleDOI
18 Jan 1991-Science
TL;DR: A systematic study of silicon-29 chemical shifts for SiVI has revealed empirical correlations between shift and structure that are useful in understanding several new calcium silicates.
Abstract: Most of the earth's mantle is made up of high-pressure silicate minerals that contain octahedrally coordinated silicon (SiVI), but many thermodynamically important details of cation site ordering remain unknown. Silicon-29 nuclear magnetic resonance (NMR) spectroscopy is potentially very useful for determining short-range structure. A systematic study of silicon-29 chemical shifts for SiVI has revealed empirical correlations between shift and structure that are useful in understanding several new calcium silicates. The observed ordering state of a number of high-pressure magnesium silicates is consistent with the results of previous x-ray diffraction studies

77 citations


Journal ArticleDOI
TL;DR: The authors examined the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand.
Abstract: This study examines the depletion of ferromagnesian silicate minerals from a sequence of thin, distal, mainly rhyolitic tephra layers of Holocene age preserved in an acid peat bog (Kopouatai), North Island, New Zealand. The rate of such depletion has been fast, as indicated by the complete loss of biotite from one tephra layer (Kaharoa Tephra), in which it is normally dominant, in only ca. 770 yr. Chemical dissolution is advocated as the likely cause for the depletion, with amphiboles and other mineral grains commonly showing etch pits, microcaves, and other characteristic surface solution features. Theoretical thermodynamic and kinetic models show a marked increase in the rate of dissolution of all ferromagnesian minerals under conditions of low pH (< 4), but that where silica concentrations in solution are high the relative proportions of minerals remaining are unaffected. However, where concentrations of dissolved silica are low, as in most bog environments, the relative proportions of ferromagnesian minerals are affected as well as absolute amounts being decreased. Amphiboles are depleted relative to pyroxenes, consistent with kinetic studies. The results show that the identification and correlation of tephras on the basis of relative abundances of ferromagnesian minerals alone may be unreliable, and emphasise the need to use multiple criteria in such studies.

63 citations


Journal ArticleDOI
01 May 1991
TL;DR: In this paper, an atomistic model was used to simulate the structure, lattice dynamics and thermodynamics of silicate minerals, including albite, diopside, forsterite, pyrope, quartz and wollastonite.
Abstract: We use an atomistic model to simulate the structure, lattice dynamics and thermodynamics of silicate minerals. Our approach uses the Born model of a solid, in which the interaction between atoms is described by an interatomic pair potential. We have extended the study of thermodynamics to its very limit by looking at the subtle reaction of oxygen isotope exchange. We have modelled equilibria involving the important metamorphic minerals; albite, diopside, forsterite, pyrope, quartz and wollastonite. The predicted structural and thermodynamic data for these silicates are in very good agreement with the observed values. In addition, we predict not only the correct direction for the phase equilibria for oxygen isotope exchange, but also fractionation factors for the reaction to within a factor of two of the available experimental data. Hence, the potentials used in our approach have shown excellent transferability and have performed very well against the most stringent of tests.

63 citations


Journal ArticleDOI
TL;DR: In this article, the structural environment around Th4+ in several silicate glasses containing 1-3 wt% Th4+) was investigated using Extended X-ray Absorption Fine Structure (EXAFS) spectroscopy.

39 citations


Journal ArticleDOI
TL;DR: In this paper, the authors used a transmission electron microscope (TEM) with energy dispersive spectrometry (EDS) to study the effect of reversible ion exchange on broken bonds and outer planar surfaces.

36 citations


Journal ArticleDOI
TL;DR: In this article, a study was made of the chemical fractionation associated with four cases of anatectic segregation of low melt-fraction cordieritic granites from migmatized meta-greywackes.

Journal Article
TL;DR: In this article, the behavior of several common minerals in a pure sodium hydroxide solution was evaluated by the means of two experiments, and the results showed that the most stable phases were found to be the iron and magnesium silicates.
Abstract: The pH of the pore solution existing within concretes or lime-treated soils normally exceeds 12. When exposed to a solution witl a pH over 10, several rock-forming and soilforming minerals are unstable, and dissolve with or without precipitation, depending on the nature and concentration of species in solution. In concrete, made with a typical cement containing 0.7a/o to l9o alkalis, after a few days, the composition of the liquid phase is dominated by sodium, potassium and hydroxide ions. In this study, the behavior of several common minerals in a pure sodium hydroxide solution was evaluated by the means of two experiments. First, mineral fragments were immersed in a lN NaOH solution at 23oC for 265 days, then at 80oC for 7 days. The specimens were regularly analyzed with a SEM-EDX system. Secondly, the release of silica by silicate minerals in a lN NaOH solution was measured by means of the Chemical Method ASTM C 289 test (80'C, 24 hours). Of all rhe silicate minerals tested, the microcryslalline variety of silica, chert, was the most unstable phase. Significant quantities of silica also were released by quartz and feldspars. Iron and magnesium silicates were found to be the mosr stable phases in the NaOH solution. Among the other minerals investigated, dolomite, siderite and gypsum are classified as highly reactive in the alkaline solution.

Journal ArticleDOI
TL;DR: In this article, the geothermal fluids in seven Japanese geothermal systems are tested for attainment of aqueous and gaseous equilibrium, and the results show that the (Mg2+)/(K+)2 activity ratio of high temperature geothermal fluid of Japan can be represented by the reaction involving Mg-chlorite and K-bearing silicate minerals, though at lower temperatures other reactions may be responsible.
Abstract: The geothermal fluids in seven Japanese geothermal systems are tested for attainment of aqueous and gaseous equilibrium. The pH of fluids in the geothermal reservoir is approximately buffered by the assemblage K-feldspar–K-mica–quartz. (Na+)/(K+) and (Na+)/√(Ca2+) activity ratios are thermodynamically approximated by reactions between albite and K-feldspar, and between albite and anorthite (or Ca-zeolites), respectively. The (Mg2+)/(K+)2 activity ratio of high temperature geothermal fluids of Japan can be, represented by the reaction involving Mg-chlorite and K-bearing silicate minerals, though at lower temperatures other reactions may be responsible. The geothermal fluids are also commonly saturated with respect to anhydrite and calcite. A small amount of steam loss in the reservoir does not significantly affect the aqueous composition of the fluids. The partial pressure of CO2 is controlled by the reaction involving calcite, K-bearing silicate minerals, and albite or Ca-zeolite in geothermal systems which are not affected by steam loss and dilution. Equilibrium between CH4, CO2 and H2 is attained at high temperatures but not maintained to lower temperatures in most Japanese geothermal systems. The H2/H2S ratio is probably equilibrated with Fe-bearing minerals. Gaseous compositions are very good indicators to identify processes in the geothermal reservoir, such as boiling and dilution. Lastly, the major aqueous composition and pH of Japanese neutral Na-Cl type geothermal fluid are predictable if two variables (e.g., temperature and one of the cation activities) are provided.

Journal ArticleDOI
TL;DR: The oxygen and hydrogen isotope composition of hydrothermal fluids associated with the Variscan granites of southwest England has been inferred from analysis of various silicate minerals (predominantly quartz) and by direct analysis of fluid inclusions within quartz and fluorite as mentioned in this paper.
Abstract: The oxygen and hydrogen isotope composition of hydrothermal fluids associated with the Variscan granites of southwest England has been inferred from analysis of various silicate minerals (predominantly quartz) and by direct analysis of fluid inclusions within quartz and fluorite. These data have been combined with the results of a fluid inclusion study to develop a model for the origin and evolution of hydrothermal fluids in the region. Magmatic fluids expelled from the granites had compositions in the range 6D = -65 to -15%o, and 6180 = 9 to 13%o. Respective temperature, salinity, fluid 6D, and fluid 8180 values for the (i) early Sn-W mineralization, (ii) later Cu-Pb-Zn sulphide mineralization, and (iii) latest 'crosscourse' Pb-Zn-F mineralization are: (i) 230-400 ~ 5-15 wt.% NaC1 equiv,, -39 to -16%o, and 7.0 to 11.2%o, (ii) 220-300 ~ mostly 2-8 wt.% NaC1 equiv., -41 to -9%0, and 2.3 to 8.1%o, and (iii) 110-150~ 22-26 wt.% NaC1 equiv., -45 to +2%0, and -1.8 to +5.5%o. These data highlight the important role of both magmatic fluids exsolved from the crystallizing granite, and basinal brines circulating within restricted fracture systems.

Journal ArticleDOI
TL;DR: In this paper, the partial charges on Si atoms in silicate and aluminosilicate anionic structures were calculated and a correlation between the Si atom partial charge and its experimentally observed chemical shift assists in the assignment of {sup 29}Si NMR peaks due to soluble anions.
Abstract: {sup 29}Si and {sup 27}Al spectroscopies were used to characterize dilute, highly alkaline tetrapropylammonium (TPA) aluminosilicate solutions. The solution compositions ranged from 0.1 to 2 mol % SiO{sub 2}, silicate ratios (R = (SiO{sub 2})/((TPA){sub 2}O)) from 0.05 to 1, and Si/Al molar ratios from 0.25 to 5. {sup 29}Si NMR resonances were observed for Al incorporation into the dimer, linear trimer, cyclic trimer, branched cyclic trimer, double three-membered ring (D3R), and double four-membered ring (D4R) anions. In aluminosilicate solutions with 2 mol % SiO{sub 2}, silicate ratios of less than 1.5 lead to the stabilization of D3R(1Al) anions. The addition of DMSO to TPA aluminosilicate solutions provides the solutions with a high concentration of D3R(1Al) and D4R(1Al) anions. Semiempirical quantum mechanical calculations were performed to calculate the partial charges on Si atoms in silicate and aluminosilicate anionic structures. A correlation between the Si atom partial charge and its experimentally observed chemical shift assists in the assignment of {sup 29}Si NMR peaks due to soluble aluminosilicates.

Journal ArticleDOI
TL;DR: In this paper, Maliva et al. found that up to 58% of the silicate grains in the laminar zone of the petro calcic horizon have dissolution features, such as embayed and serrated edges.
Abstract: In the petrocalcic horizon of a middle Pleistocene soil in southern New Mexico, up to 58% of the silicate grains have dissolution features, such as embayed and serrated edges. The purpose of this study was to determine if pressure solution produced the dissolution features. Samples were analyzed in thin section using light and electron microscopy, and by measuring pH and Si concentration of saturated paste extracts. Four lines of evidence support the pressure-solution mechanism in the petrocaIcic horizon: (i) silicate grains are smooth where they contact pores, but serrated where they contact calcite; (ii) dissolution pits on silicate grains generally match the shapes of impacted calcite crystals; (iii) silicate grains are concentrated into horizonal layers in the upper petrocalcic horizon, which testifies to the pressure generated by crystallizing calcite; and (iv) outside the petrocaIcic horizon where crystallization pressure is less, silicate grains coated with calcite crystals have fewer dissolution features than grains in the petrocalcic horizon. No relationship was apparent between silicate-grain dissolution and petrocaIcic-horizon pH or Si concentration. The pH (7.6) was below, and the Si concentration (8.6 mg L-l) was above the levels required for dissolution. Thus, pressure generated by crystallizing calcite appears to have caused dissolution features on the silicate grains in the petrocalcic horizon. SILICATE GRAINS with dissolution features occur in both carbonate rocks and calcareous soils (Walker, 1957, 1960, 1962; Swineford et aI., 1958; Friedman et aI., 1976; Halitim et ai., 1983; Burley and Kantorowicz, 1986; Reheis, 1988a,b). Dissolution can result from high pH of interstitial pore solutions (Walker, 1962; Friedman et aI., 1974) and from pore solutions that are Si undersaturated with respect to silicate minerals (Rai and Lindsay, 1975; Walker et aI., 1978). Pressure solution is another mechanism that causes dissolution of silicate grains and is based on the principle that silica solubility increases as pressure is applied to silicate grains (Weyl, 1959; Maliva and Siever, 1988a, 1988b; Dewers and Ortoleva, 1990). In the case of silicate grains in a calcite matrix, the pressure is generated by precipitating calcite crystals that grow, contact, and push against silicate grains. The pressuresolution mechanism can account for the dissolution of silicate grains where they contact calcite, and dissolution pits that match the shapes of impacted calcite crystals (Maliva and Siever, 1988b). Pressure solution also eliminates the need to have unverifiably high pH to account for silicate-grain dissolution. In a soil of the lower La Mesa geomorphic surface in southern New Mexico (Fig. 1), up to 58% of the silicate grains in the laminar zone of the petro calcic horizon have dissolution features. The few silicate grains with dissolution features above and below the Dep. of Agronomy and Horticulture, Box 30003, New Mexico State Univ., Las Cruces, NM 88003. Contribution from New Mexico State Agric. Exp. Stn., Journal Article no. 1551. Received 20 Sept. 1990. *Corresponding author. Published in Soil Sci. Soc. Am. J. 55:1625-1629 (1991). petrocalcic horizon have smooth embayments and appear to be the result of chemical weathering. Silicate grains in the petrocalcic horizon, however, have serrated edges with dissolution pits that generally match the shapes of impacted calcite crystals. Such dissolution features appear to be the result of pressure solution. The purpose of this study was to test the hypothesis that dissolution of silicate grains in the petrocalcic horizon resulted from pressure generated by crystallizing calcite. MATERIALS AND METHODS The studied pedon is located within the boundary of the 1036-km2 USDA-SCS Desert Soil-Geomorphology Project in southern New Mexico (Fig. I) (Gile and Grossman, 1979; Gile et aI., 1981). The silicate grains, mainly quartz and feldspars, are part ofthe noncalcareous alluvium (Camp Rice Formation) deposited by the ancestral Rio Grande during middle Pleistocene time (Gile et aI., 1981; Seager et aI., 1987). The source of calcite that formed the petrocalcic horizon, a Stage IV carbonate accumulation (Gile et aI., 1966), is attributed to calcareous dust and Ca2+ dissolved in rain water (Gile and Grossman, 1979). The soil is classified as a coarse-loamy, mixed, thermic Typic Haplargid. The soil and underlying parent sediments of the Camp Rice Formation were described in a 4.5 by 38 m trench. Twenty-six horizons were designated (Table I). . 1625 Soil peds were impregnated with epoxy, mounted on glass slides, and ground to 0.03 mm based on quartz first-order gray interference colors (Adams et aI., 1984, p.97-98.). Quartz, feldspar, and lithic fragments were identified by staining (Bailey and Stevens, 1960) and optical properties (Scholle, 1981; Shelley, 1983). The percentages of quartz, feldspar, and lithic fragments were determined for 16 horizons by counting an average of 330 grains larger than 25 ~m for each thin section on a I by I mm grid spacing (Table I). Samples examined with scanning electron microscopy (SEM) were sputter coated with Au and viewed with a Philips electron microscope (Philips Electronics, Eindhoven, the Netherlands) oat 7 to 15 kV. The 16 horizons were chosen based on their coverage of the main horizon types. Fig. 1. Location of the studied lower La Mesa pedon (arrow) (after Gile et ai., 1981, p. 112). 1626 SOIL SCI. SOC. AM. J., VOL. 55, NOVEMBER-DECEMBER 1991 Table 1. Selected mineralogical, physical, and chemical properties of the lower La Mesa soil.

Journal Article
TL;DR: In this article, the partial pressures of the mixtures of H2O, CO2, CH4, CO, H2, 02, and graphite saturation have been derived to predict devolatilization of the lower crust.
Abstract: Fluids in the lithosphere are treated as mixtures of H2O, CO2, CH4, CO, H2, 02. The following three conditions have been utilised to determine the partial pressures of these constituents: (1) a fugacity of H2 as indicated by biotite feldspar magnetite fluid assemblages with mineral compositions representative of granulites, (2) oxygen fugacity as specified by the quartz fayalite magnetite fluid reference assemblage, and (3) graphite saturation. Fluid pressure equal to lithostatic pressure has not been assumed in the calculation in order to derive the relationship between fluid pressure and lithostatic pressure on the basis of mineral compositions. For oxidation levels along the quartz fayalite magnetite fluid reference assemblage, there are significant segments above 500oC along pressure temperature time paths where calculated fluid pressure exceeds lithostatic pressure, and devolatilization is predicted for graphite-saturated rocks containing typical biotite solidsolutions. At lower oxygen fugacities, the condition for devolatilization requires higher temperature for a given depth; at higher oxygen fugacities expected in some granulite-facies rocks (since orthopyroxene is more stable under these conditions than fayalite), the region of devolatilization increases by expanding to lower temperatures for a given depth. Devolatilization of the lower crust is predicted by these calculations, with the hydrogen reservoir (held in hydrous silicate minerals) and the carbon reservoir (excess graphite) being depleted in the process. The commonly observed CO2-rich fluid inclusions in granulites are consistent with the type of residual fluids expected from the process described above.

Journal ArticleDOI
TL;DR: The 3.2 Ga Kaap Valley tonalite (KVT) is a homogeneous hornblende+biotite tonalites which is surrounded by the Barberton greenstone belt as discussed by the authors, with the highest proportion of hydrous phases and carbonate occurring along major shear zones within the KVT and the sheared contact with the greenstone material.

Journal ArticleDOI
TL;DR: In this article, Peters' vanadate method for the determination of Fe(II) in silicate minerals was investigated to see if improvements could be made in the accuracy, precision and speed of the analysis.

Journal ArticleDOI
TL;DR: In this paper, a study has been made on the wetting characteristics of quartz and several other silicate minerals and road stones used in bituminous roads using the two-liquid phase method.

Journal ArticleDOI
TL;DR: In this article, micro-thermometric and Raman spectroscopic data on fluid inclusions trapped in quartz sulfide veins adjacent to the intrusive contact indicate that three fluid types existed in the thermal aureole of the Devonian McGerrigle pluton: (1) H 2 O (2) H2 O + CO 2, and (3) CH 2 ± N 2 ± CO 2.


01 Mar 1991
TL;DR: The major components of the Rustler Formation, as determined by x-ray diffraction (XRD), are halite, anhydrite, gypsum, dolomite, magnesite, quartz, and clay as discussed by the authors.
Abstract: The mineralogy of the Rustler Formation is a critical element in many of the radionuclide release models for the Waste isolation Pilot Plant (WIPP), and it is necessary to know the abundances of the various minerals present, their compositions, their textures and locations with respect to water-bearing features, and their interrelationships. Clay mineralogy in particular is of vital importance because of the ability of clay minerals to sorb contaminant cations. Furthermore, the minerals present in the different units of the Rustler Formation are possible sources for solutes present in waters taken from various boreholes in the vicinity of the WIPP site. This report characterizes the mineralogy of the Rustler Formation as represented in core from borehole WIPP-19. The major components, as determined by x-ray diffraction (XRD), are halite, anhydrite, gypsum, dolomite, magnesite, quartz, and clay. Minor components include calcite, pyrite, feldspar and phyllosilicates of metamorphic origin (muscovite, biotite, and chlorite). Clay minerals, identified by XRD, include illite, serpentine, chlorite, and mixed-layer chlorite/smectite (including corrensite). In general, this study should be considered a detailed analysis of the Rustler section mineralogy. It is unlikely that any other minerals are present elsewhere in the Rustler Formation in any great quantity. Abundances of individualmore » minerals may vary considerably in other areas of the formation. 20 refs., 39 figs., 5 tabs.« less

Patent
04 Mar 1991
TL;DR: The use of a bacterial cellulose as a depressant for readily flotatable silicate minerals in an ore flotation process was proposed in this paper, where the cellulose was used as a talcose mineral depressant.
Abstract: The invention resides in the use of a bacterial cellulose as a depressant for readily flotatable silicate minerals in an ore flotation process. Depending on the particular ore being treated, from 0.2-1.5 lb/ton of ore of the bacterial cellulose is effective as a talcose mineral depressant. Usually only about 0.10-0.25 lb/ton of the bacterial cellulose will produce optimum results.


Book ChapterDOI
K.H. Tan1
01 Jan 1991
TL;DR: In this article, the results indicated that the dissolution of Si and Al from the silicate minerals yielded a parabolic curve, and dissolution of Ca and Fe from hornblende, and K from microcline was also curvilinear in regression.
Abstract: Biochemical decomposition of primary minerals was investigated by shaking calcite, hornblende and microcline with fulvic (FA) or humic acid (HA) at pH 70 and 25 for 0 to 885 hrs Silicon, Al, Fe, K and Ca released were determined in the extracts by atomic absorption spectroscopy Changes in mineral structure were studied by X-ray diffraction analysis, petrographic and scanning electron microscopy The results indicated that the dissolution of Si and Al from the silicate minerals yielded a parabolic curve The dissolution of Ca and Fe from hornblende, and K from microcline was also curvilinear in regression X-ray diffraction peaks of the minerals were decreased considerably in intensities as a result of attack by HA Petrographic and scanning electron microscopy showed the presence of a diffusion layer on the surfaces of microcline and hornblende after treatments with HA This layer acted as a barrier, slowing down further dissolution of the minerals with time In contrast, dissolution analysis of calcite indicated that the release of Ca by FA and HA with time was linear in regression The release of this element was enhanced considerably at pH 25 X-ray diffraction peaks were decreased in intensities as a result of treatments of the mineral with HA However, no indications were obtained by petrographic and scanning electron microscopy for formation of diffusion layers on the surface of the calcite crystals On the contrary, these analyses showed the disintegration of calcite into small particles after attack by HA

Journal ArticleDOI
TL;DR: In this article, the Si-O system in the fragment ions in LMMS spectra suggests the pattern of tetrahedral SiO4, which can be expressed as SiOn (n ≤ 4), SimO3m±1 for inosilicates, SimO5/2m±(m/2+1).
Abstract: Silicates have several kinds of silicate tetrahedral network. Thirteen kinds of silicate minerals with 5 kinds of network structures have been analyzed with laser microprobe mass spectrometry (LMMS) and their spectra showed characteristic patterns according to their network structures. The Si-O fragment ions can be expressed as SiOn (n ≤ 4) for nesosilicates, SimO3m±1 for inosilicates, SimO5/2m±(m/2+1) for phyllosilicates and SimO2m±(m+1) for tectosilicates. The Si-O system in the fragment ions in LMMS spectra suggests the pattern of network of tetrahedral SiO4.

Book ChapterDOI
A. Tsuchiyama1
01 Jan 1991
TL;DR: In this article, a simple but most fundamental system Mg-Si-O-H with forsterite vaporization source was used to obtain euhedral whiskers of forsterites.
Abstract: Condensation experiments were performed in the simple but most fundamental system Mg-Si-O-H with forsterite vaporization source. At temperatures above about 1000°C, euhedral crystals of forsterite (Mg2Si04) of a few μrn were formed. These crystals are similar to olivines in Allende matrix. At temperatures below about 1000°C, whiskers of forsterite and enstatite (MgSiO3) were formed by vapor-liquid-solid growth mechanism. These whiskers are different from enstatite whiskers in interplanetary dust, which were probably formed at small super coolings


Journal ArticleDOI
TL;DR: In this article, a two-stage reaction process for the formation of {[(CH3)3SiO]10Si8O11}[Q8M10; Q = SiO4/2, M =(CH 3)3 SiO1/2] has been outlined, which includes silicic acid polymerisation and polyorganosiloxane (QM polymer) redistributions.
Abstract: The preparation of three-dimensional silicate organosiloxane hybrids by the controlled polymerisation of monosilicic acids derived from silicate minerals such as olivine has been studied. A two-stage reaction process, for the formation of {[(CH3)3SiO]10Si8O11}[Q8M10; Q = SiO4/2, M =(CH3)3SiO1/2] has been outlined, which includes silicic acid polymerisation and polyorganosiloxane (QM polymer) redistributions. The structure of Q8M10 has been characterised and shown to be a major product of the partial trimethylsilylation of the minerals olivine or dioptase.