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1.
When quenched metastable wüstite (Fe .924O and Fe .947O) is held at 300°C at pressures up to 200 kbar in a diamond anvil cell, a mixture of magnetite, metallic iron and wüstite is found. We interpret this to indicate that magnetite plus metallic iron constitute the stable phase assemblage at pressures and temperatures below this boundary is stoichiometric FeO ( ) at pressures below 110 kbar at 300°C. However, just below the boundary in the pressure range 110 kbar to 200 kbar at 300°C, the residuál wüstite is non-stoichiometric ( ). Data collected at pressures and temperatures above the boundary indicate that non-stoichiometric wüstite (Fe xO) plus metallic iron constitute the stable phase assemblage and that the value of x in Fe xO increases as pressure is increased isothermally to 100 kbar and then decreases as pressure is increased above 100 kbar. 相似文献
2.
K and Rb distributions between aqueous alkali chloride vapour phase (0.7 molar) and coexisting phlogopites and sanidines have been investigated in the range 500 to 800°C at 2000 kg/cm 2 total pressure.Complete solid solution of RbMg 3AlSi 3O 10(OH) 2 in KMg 3AlSi 3O 10(OH) 2 exists at and above 700°C. At 500°C a possible miscibility gap between approximately 0.2 and 0.6 mole fraction of the Rb end-member is indicated.Only limited solid solution of Rb AlSi 3O 8 in KAlSi 3O 8 has been found at all temperatures investigated.Distribution coefficients, expressed as in solid/(Rb/K) in vapour, are appreciably temperature-dependent but at each temperature are independent of composition for low Rb end-member mole fractions in the solids. The determined values and their approximate Rb end-member mole fraction ( ) ranges of constancy are summarized as follows: (°C) | (°C)T | | | | | | 500 | | 0–0.2 | | 0–0.07 | | 700 | | 0–0.2 | | 0–0.1 | | 800 | | 0–0.2 | | 0–0.1 | 相似文献
3.
Thermodynamic calculations for selected silicate-oxide-fluorite assemblages indicate that several commonly occurring fluorite-bearing assemblages are restricted to relatively narrow fields at constant P?T. The presence of fayalite-ferrohedenbergite-fluorite-quartz ± magnetite and ferrosalite-fluorite-quartz-magnetite assemblages in orthogneisses from Au Sable Forks, Wanakena and Lake Pleasant, New York, buffered fluorine and oxygen fugacities during the granulite facies metamorphism in the Adirondack Highlands. These buffering assemblages restrict to 10 ?29 ± 1 bar and to 10 ?16 ± 1 bar at the estimated metamorphic temperature of 1000K and pressure of 7 kbar. The assemblage biotite-magnetite-ilmenite-K-feldspar, found in the same Au Sable Forks outcrop as the fayalite-fluorite-ferrohedenbergite-quartz-magnetitie assemblage, restricts H 2O fugacities to less than 10 3·3 bar. These fugacities limit H 2 and HF fugacities to less than 10 1 bar for the Au Sable outcrop. The data indicate that relative to H 2O, O 2, H 2, F 2 and HF are not major species in the fluid equilibrated with Adirondack orthogneisses. The calculated F 2 fugacilies are similar to the upper limits possible for plagioclase-bearing rocks and probably represent the upper limit for metamorphism in the Adirondacks and in other granulite facies terranes. 相似文献
4.
The carbonato and hydrogencarbonato complexes of Mg 2+ were investigated at 25 and 50° in solutions of the constant ClO 4? molality (3 M) consisting preponderantly of NaClO 4. The experimental data could be explained assuming the following equilibria: Mg 2+ + CO 2B + H 2O ag MgHCO +3 + H +, , Mg2+ + 2 CO 2g + 2 H 2Oag Mg(HCO 3) 02 ± 2 H +, , ?15.37 ± 0.39 (50°), Mg 2+ + CO 2g + H 2Oag MgCO 03 + 2 H +, ,?15.23 ± 0.02 (50°), with the assumption γMgCO30 = γMg(HCO3)02, ΔG0(I = 0) for the reaction MgCO 03 + CO 2g + H 2O = Mg(HCO 3) 02 was estimated to be ?3.9 1 ± 0.8 6 and 0.6 ± 2.4 kJ/ mol at 25 and 50°C, respectively. The abundance of carbonate linked Mg(II) species in fresh water systems is discussed. 相似文献
5.
Potentiometric measurements in dilute sodium borate solutions with added alkali earth chlordie salts yield the following expressions for the dissociation constants of alkali earth borate ion pairs from 10 to 50°C: where T is in °K. Enthalpies for the dissociation reactions at 25°C are less than 1 kcal./mole for all the alkali earth borate ion pairs.Values for p K(NaH 2BO 3°) from 5 to 55°C computed from the experimental data of Owen and King are in good agreement with those determined potentiometrically. The average value from both methods is 0.22 ± 0.1 at 25°C.Application to seawater of computed p K's for MgH 2BO 3+, CaH 2BO 3+ and NaH 2BO 30 yields an apparent dissociation constant for boric acid of 8.73 vs. 8.70 measured by Lyman, 8.68 by Buch and 8.73 by Byrne and Kester. 相似文献
6.
A differential rate equation for silica-water reactions from 0–300°C has been derived based on stoichiometry and activities of the reactants in the reaction SiO 2(s) + 2H 2O(l) = H 4SiO 4(aq) where ( ) = (the relative interfacial area between the solid and aqueous phases/the relative mass of water in the system), and k+ and k? are the rate constants for, respectively, dissolution and precipitation. The rate constant for precipitation of all silica phases is and Eact for this reaction is 49.8 kJ mol ?1. Corresponding equilibrium constants for this reaction with quartz, cristobalite, or amorphous silica were expressed as . Using , k was expressed as and a corresponding activation energy calculated: | a | b | c | Eact(kJ mol -1) | | Quarts | 1.174 | -2.028 x 103 | -4158 | 67.4–76.6 | | α-Cristobalite | -0.739 | 0 | -3586 | 68.7 | | β-Cristobalite | -0.936 | 0 | -3392 | 65.0 | | Amorphous silica | -0.369 | -7.890 x 10-4 | 3438 | 60.9–64.9 | 相似文献
7.
The F contents of a number of Apollo 14 and 15 samples range from less than a ppm for anorthosite rock fragments to ~165 ppm for some soils and breccias. Apollo 15 soils tend to have lower F contents (50–70 ppm) than soils from other sites. In most cases samples were run simultaneously with W-1 in which F was determined to be 216 (±11) ppm.The ratio is 0·032 ± 0·005 in soils and rocks. A correlation exists in soils between F, P 2O 5, and that fraction of the Cl which is insoluble in hot water. The ratio in soils and rocks, though different, requires that the phosphate phase involved be fluorapatite; this is consistent with mineralogical observations. F, like Cl, is correlated with KREEP elements at all sites for which data are available. 相似文献
8.
Karibibite (ideally, Fe 2As 4O 9) occurs in vugs in massive loellingite of the Karibib pegmatite area, South West Africa. It is brownish yellow and finely fibrous. The thickness of the soft, single fibers is less than 1 micron, unsuitable for single-crystal X-ray study. Electron diffraction and X-ray powder pattern indicate that the mineral is orthorhombic, with . The space group cannot be given. The mineral is paramagnetic with yellow fluorescence and is pleochroic with γ > 2.10, α = 1.96, 2V α large, d = 4.07. It is soluble in acids and alkali hydroxide. Decomposition starts around 320 °C. The infra-red absorption spectrum indicates absence of AsO 4 groups. The mineral is classified tentatively as an oxide or arsenite. 相似文献
9.
The spectrophotometric measurements of chloro complexes of lead in aqueous HCl, NaCl, MgCl 2 and CaCl 2 solutions at 25°C have been analyzed using Pitzer's specific interaction equations. Parameters for activity coefficients of the complexes PbCl +, PbCl 20 and PbCl 3? have been determined for the various media. Values of , and were obtained for the cumulative formation constants. [ ]. These values are in reasonable agreement with literature data. The Pitzer parameters for the PbCl ion pairs in various media were used to calculate the speciation of Pb 2+ in an artificial seawater solution. 相似文献
10.
Light hydrocarbon (C 1-C 3) concentrations in the water from four Red Sea brine basins (Atlantis II, Suakin, Nereus and Valdivia Deeps) and in sediment pore waters from two of these areas (Atlantis II and Suakin Deeps) are reported. The hydrocarbon gases in the Suakin Deep brine ( T = ~ 25° C, , ) are apparently of biogenic origin as evidenced by ) ratios of ~ 1000. Methane concentrations (6–8 μl/l) in Suakin Deep sediments are nearly equal to those in the brine, suggesting sedimentary interstitial waters may be the source of the brine and associated methane.The Atlantis II Deep has two brine layers with significantly different light hydrocarbon concentrations indicating separate sources. The upper brine ( T = ~ 50° C, , CH4 = ~ 155 μl/ l) gas seems to be of biogenic origin [ ], whereas the lower brine ( T = ~ 61° C, , CH4 = ~ 120 μl/ l) gas is apparently of thermogenic origin [ ]. The thermogenic gas resulting from thermal cracking of organic matter in the sedimentary column apparently migrates into the basin with the brine, whereas the biogenic gas is produced in situ or at the seawater-brine interface. Methane concentrations in Atlantis II interstitial waters underlying the lower brine are about one half brine concentrations; this difference possibly reflects the known temporal variations of hydrothermal activity in the basin. 相似文献
11.
The fractionation factors ( ) for the reduction of CO 2 to CH 4 by pure cultures of methane-producing bacteria are, for Methanosarcina barkeri at 40°C, 1.045 ± 0.002; for Methanobacterium strain M.o.H. at 40°C, 1.061 ± 0.002; and, for Methanobacterium thermoautotrophicum at 65°C, 1.025 ± 0.002. These observations suggest that the acetic acid used by acetate dissimilating bacteria, if they play an important role in natural methane production, must have an intramolecular isotopic fractionation ( ) approximating the observed fractionation. 相似文献
12.
Optical and analytical studies were performed on 400 N 2 + CO 2 gas bearing inclusions in dolomites and quartz from Triassic outcrops in northern Tunisia. Other fluids present include brines (NaCl and KCl bearing inclusions) and rare liquid hydrocarbons. At the time of trapping, such fluids were heterogeneous gas + brine mixtures. In hydrocarbon free inclusions the mole ratio was determined using two different non-destructive and punctual techniques: Raman microprobe analysis, and optical estimation of the volume ratios of the different phases selected at low temperatures. In the observed range of compositions, the two methods agree reasonably well.The N 2 + CO 2 inclusions are divided into three classes of composition: (a) : Liquid nitrogen is always visible at very low temperature and homogenisation occurs in the range ?151°C to ? 147°C (nitrogen critical temperature) dry ice (solid CO 2) sublimates between ?75°C and ?60°C; (b) : liquid nitrogen is visible at very low temperature but dry ice melts on heating; liquid and gas CO 2 homogenise to liquid phase between ?51°C to ?22°C; (c) : liquid nitrogen is not visible even at very low temperature (?195°C) and liquid and gas CO 2 homogenise to liquid phase between ?22°C and ?15°C. The observed phases changes are used to propose a preliminary phase diagram for the system CO 2-N 2 at low temperatures.Assuming additivity of partial pressures, isochores for the CO 2-N 2 inclusions have been computed. The intersection of these isochores with those for brine inclusions in the same samples may give the P and T of trapping of the fluids. 相似文献
13.
Mineral-aqueous solution equilibria for the assemblages talc-quartz, tremolite-talc-quartz, diopside-tremolite-quartz, wollastonite-diopside-quartz and wollastonite-quartz have been studied at 2 kb total pressure, 500° to 700°C and chloride concentrations from 0.03 to 6.0 molal. Most work was at 1 m chloride. Both buffered and unbuffered data were obtained and a recalibration of the Ag-AgCl buffer is presented. Log equilibrium quotients at 500°, 600° and 700°C are respectively: Ta-Qz ( ) 2.57, 1.71, 0.73; Tr-Ta-Qz and Di-Tr-Qz ( ) 4.98, 3.99, 2.21 and 7.29, 5.30, 3.56; WoDi-Qz ( ) 3.30, 3.00, 2.79: Wo-Qz ( ) 5.15, 3.95, 2.68. Mineral stability fields plotted in terms of these concentration data more tangibly represent the compositional character of real systems and the mass transfer capabilities of their fluids than do the analogous theoretical activity diagrams.Overall dissociation constants of MgCl 2 and CaCl 2 were calculated from the experimental data using the calculated ionic activity constants for the reactions and the established dissociation constants of HCl. The negative log values are respectively: 3.88. 6.63, 9.20 for CaCl 2 and 4.60, 7.54, 10.37 for MgCl 2 at 500°, 600° and 700°C, 2 kb. The Ca values are about an order of magnitude more positive than the conductance-derived values by Frantz and Marshall (1982).The phase relations developed in this study have application to the genesis of talc, tremolite, and diopside-bearing assemblages in some regional metamorphic rocks, but more specifically to the calcsilicate skarn assemblages of many metasomatic aureoles. The equilibrium fluids are characterized by high concentrations of Ca relative to Mg and increasing ratios with decreasing temperatures. The stability fields of talc, tremolite, and quartz expand relative to those of diopside and wollastonite with decreasing temperature, hence their more common appearance as retrograde products in skarn systems. 相似文献
14.
Calculations based on approximately 350 new measurements (Ca T-PCO 2) of the solubilities of calcite, aragonite and vaterite in CO 2-H 2O solutions between 0 and 90°C indicate the following values for the log of the equilibrium constants KC, KA, and KV respectively, for the reaction CaCO 3(s) = Ca 2+ + CO 2?3: where T is in oK. At 25°C the logarithms of the equilibrium constants are ?8.480 ± 0.020, ?8.336 ± 0.020 and ?7.913 ± 0.020 for calcite, aragonite and vaterite, respectively.The equilibrium constants are internally consistent with an aqueous model that includes the CaHCO +3 and CaCO 03 ion pairs, revised analytical expressions for CO 2-H 2O equilibria, and extended Debye-Hückel individual ion activity coefficients. Using this aqueous model, the equilibrium constant of aragonite shows no PCO 2-dependence if the CaHCO +3 association constant is between 0 and 90°C, corresponding to the value logKCahco+3 = 1.11 ± 0.07 at 25°C. The CaCO 03 association constant was measured potentiometrically to be between 5 and 80°C, yielding logKCaCO03 = 3.22 ± 0.14 at 25°C.The CO 2-H 2O equilibria have been critically evaluated and new empirical expressions for the temperature dependence of KH, K1 and K2 are , and logK2 = ?107.8871 ? 0.03252849 T + 5151.79/ T + 38.92561 logT ? 563713.9/ T2 which may be used to at least 250°C. These expressions hold for 1 atm. total pressure between 0 and 100°C and follow the vapor pressure curve of water at higher temperatures.Extensive measurements of the pH of Ca-HCO 3 solutions at 25°C and 0.956 atm PCO 2 using different compositions of the reference electrode filling solution show that measured differences in pH are closely approximated by differences in liquid-junction potential as calculated by the Henderson equation. Liquid-junction corrected pH measurements agree with the calculated pH within 0.003-0.011 pH.Earlier arguments suggesting that the CaHCO +3 ion pair should not be included in the CaCO 3-CO 2-H 2O aqueous model were based on less accurate calcite solubility data. The CaHCO +3 ion pair must be included in the aqueous model to account for the observed PCO 2-dependence of aragonite solubility between 317 ppm CO 2 and 100% CO 2.Previous literature on the solubility of CaCO 3 polymorphs have been critically evaluated using the aqueous model and the results are compared. 相似文献
15.
If the temperature of ground water is below 75°C and the partial pressure of CO 2 in the aquifer is above 10 ?4 atm, a chemical steady-state between water and felsic rocks (rather than chemical equilibrium) may be maintained. The temperature of water in the aquifer may be estimated using a modified form of the Na-K-Ca geothermometer from, . where the departure of the steady-state from equilibrium, , is a function of : . 相似文献
16.
Senegalite is orthorhombic, mm2, a:b:c:=1.296:1:1.007; , Z=4, G calc=2551; space group Pna2. The strongest lines in the powder pattern are: 5.41(7); 4.089(9); 3.834(10); 3.610(8); 2.990(9); 2.348(8); 2.070(7) 1.929(7); 1.505(7) Å. The chemical analysis: Al 2O 3 ? 46.23; Fe 2O 3 ? 0.28; P 2O 5 ? 31.85 H 2O ? 21.00; sum 99.34, gives a formula Al 2(PO 4)(OH) 3 · H 2O. Colourless optically biaxial positive, n S: α=1.562, β=1.566, γ=1.587, plane of optical axies (001), Z=a, Y=c; 2V=53°, weak dispersion r > v. Measured density 2.552. The DTA curve shows endothermic reactions at 250, 370 and 440°C corresponding to the dehydration of mineral. Infrared spectrum indicates the presence of OH and H 2O groups. Found in oxidation zone of Kouroudiako iron deposit, Senegal, associated with turquoise, augelite, wavellite and crandallite. 相似文献
17.
Potential solubility controls on phosphorus in Yellowstone National Park geothermal waters were investigated using the analytical phosphate estimates of Stauffer and Thompson (1978), the computer program, WATEQF, and adopting the equilibrium constant: for fluorapatite (FAP = Ca 5(PO 4) 3F) dissolution. The near-boiling high-Cl geyser and spring effluents are at or near saturation with respect to (with) FAP. The sixteen representative springs in this category had FAP saturation indices ( ) ranging from ? 3.2 to +4.9 and averaging +0.9. The strongly positive indices were all associated with the highly alkaline conditions resulting from adiabatic cooling in the near surface environment. Hot spring waters indicating extensive dilution (reduced Cl) by meteoric water have lower pH's, and despite PO 4 and Ca concentrations an order of magnitude higher than the geysers, are still frequently undersaturated with FAP. The travertine-depositing “Mixed-water” springs are invariably supersaturated with FAP at ground surface and at or near saturation with hydroxylapatite. Supersaturation may result from kinetic inhibition of apatite crystallization by the elevated Mg 2+, HCO 3?, and lower temperatures in these springs. The phosphates may be residuals of the meteoric dilution water.Separately, if Strübel's temperature-dependent estimates of fluorite (CaF 2) solubility are adopted, the high-Cl geysers and springs on “Geyser Hill” and at Norris are consistently undersaturated with CaF 2 at the 90–100° orifice temperatures. The apparent disequilibrium may reflect fluorite equilibration at the much higher temperatures (> 200°C) in the deeper enthalpy reservoirs. 相似文献
18.
Fractionation factors between epidote minerals and water, and between the AlO(OH) dimorphs boehmite and diaspore and water, have been determined between 150 and 650°C. Small water mineral ratios were used to minimise the effect of incongruent dissolution of epidote minerals. Waters were extracted and analysed directly by puncturing capsules under vacuum. Hydrogen diffusion effects were eliminated by using thick-walled capsules. Exchange rates are very fast between epidote and water (and between boehmite and water), complete exchange taking only minutes above 450°C but several months at 250°C. Exchange between zoisite and water (and between diaspore and water) is very much slower, and an interpolation method was necessary to determine fractionation factors at 450 and below.For the temperature range 300–650°C, the equilibrium fractionation factor ( αe) between epidote and water is independent of temperature and Fe content of the epidote, and is given by 1000 In αepidote-H2Oe = ?35.9 ± 2.5, while below 300°C 1000 In , with a ‘cross-over’ estimated to occur at around 185°C. By contrast, zoisite-water fractionations fit the relationship 1000 In .All studied minerals have hydrogen bonding. Fractionations are consistent with the general relationship: the shorter the O-H -- O bridge, the more depleted is the mineral in D.On account of rapid exchange rates, natural epidotes probably acquired their H-isotope compositions at or below 200°C, where fractionations are near or above 0%.; this is in accord with the observation that natural epidotes tend to concentrate D relative to other coexisting hydrous minerals. 相似文献
19.
Equations are developed for calculating the density of aluminosilicate liquids as a function of composition and temperature. The mean molar volume at reference temperature Tr, is given by , where the summation is taken over all oxide components except A1 2O 3, X stands for mole fraction, terms are constants derived independently from an analysis of volume-composition relations in alumina-free silicate liquids, and is the composition-dependent apparent partial molar volume of Al 2O 3. The thermal expansion coefficient of aluminosilicate liquids is given by , where terms are constants independent of temperature and composition, and is a composition-dependent term representing the effect of Al 2O 3 on the thermal expansion. Parameters necessary to calculate the volume of silicate liquids at any temperature T according to V( T) = Vrexp[ α( T- Tr)], where Tr = 1400° C have been evaluated by least-square analysis of selected density measurements in aluminosilicate melts. Mean molar volumes of aluminosilicate liquids calculated according to the model equation conform to experimentally measured volumes with a root mean square difference of 0.28 and an average absolute difference of 0.90% for 248 experimental observations. The compositional dependence of is discussed in terms of several possible interpretations of the structural role of Al 3+ in aluminosilicate melts. 相似文献
20.
The synthetic chelating agent ethylenediaminetetraacetic acid (EDTA) has been used to evaluate the stoichiometric solubility product of galena (PbS) at 298°K: This method circumvents the possible uncertainties in the stoichiometry and stability of lead sulfide complexes. At infinite dilution, , and at an ionic strength corresponding to seawater ( ), . Using the value of at infinite dilution, and the free energies of formation of HS ? and Pb 2+ at 298°K (literature values), the free energy of formation of PbS at 298°K is computed to be . Galena is shown to be more than two orders of magnitude more soluble than indicated by calculations based on previous thermodynamic data. 相似文献
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