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《地学前缘(英文版)》2023,14(1):101458
Plagioclase is the major rock-forming mineral constituting the Earth’s crust, whereas anorthite (CaAl2Si2O8) is a common minerals in lunar highlands crust, meteorites, possibly in some comets and on Mercury. Besides anorthite, two high-temperature polymorphs of CaAl2Si2O8 are known: dmisteinbergite and svyatoslavite, which are found in burnt coal dumps, meteorites and pseudotachylytes. Here we present the results of detailed studies (quenching experiments, elemental analysis, Raman spectroscopy and in situ high temperature single crystal X-ray diffraction (up to 1000 °C)) on naturally co-occurring CaAl2Si2O8 polymorphs (anorthite, dmisteinbergite and svyatoslavite) from a burnt coal dump in Kopeisk, Russia. New polymorphs were found in all natural samples and obtained upon heating of dmisteinbergite (unquenchable β-dmisteinbergite and quenchable γ-dmisteinbergite). It was shown that Ca coordination differs significantly in CaAl2Si2O8 polymorphs, resulting in a different capacity to host Ba and possibly other large ion lithophile elements. Combining our data on natural samples with the previously published data on natural and synthetic compounds, we propose a new scheme of CaAl2Si2O8 polymorphs stability. Our results indicate that CaAl2Si2O8 polymorphs could be used for temperature estimations for both Earth and planetary sciences. 相似文献
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Pascal Richet 《Physics and Chemistry of Minerals》1990,17(1):79-88
Relative-enthalpy measurements have been made on the hexagonal, tetragonal, glass and liquid phases of GeO2. The glass transition is very sensitive to the impurity content, with a T g ranging from 980 K for a pure product to 780 K for a Li-doped sample with 0.06 mol % Li. The relative C p change at T g of about 5% increases with the impurity content as a result of lower glass transition temperatures. Above 298 K the derived heat capacities are similar for all forms, with slightly higher values for the amorphous phases and two C p cross-overs at 400 and 1000 K between the hexagonal and tetragonal modifications. For both GeO2 and SiO2 the coordination state markedly affects C p and the entropy below 300 K, where the properties are much lower for the tetragonal than for the hexagonal modifications, i.e., S 298 = 39.7 vs 55.3 J/mole K and 27.8 vs 41.4 J/ mole K for GeO2 and SiO2, respectively. The high-temperature C p's of coesite and stishovite are likely similar to those of the low-pressure SiO2 forms. Finally, these results, low-temperature C p data and enthalpy-of-solution measurements have been used to derive a consistent set of thermodynamic properties for the GeO2 modifications. 相似文献
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Melting and subsolidus reactions in the system K2O-CaO-Al2O3-SiO2-H2O: corrections and additional experimental data 总被引：2，自引：0，他引：2
Melting relationships in the system K2O-CaO-Al2O3-SiO2-H2O have been reinvestigated using Schreinemakers analysis and hydrothermal experiments. The reaction sanidine+muscovite+zoisite+quartz+vapor =melt has been bracketed at 10, 15, and 20 kbars and 670–680, 680–690, and 690–700° C, respectively and it marks the lowest solidus temperatures in the system investigated.Below 10 kbars, experimental data on the beginning of melting in zoisite- or muscovite-bearing anorthite+sanidine assemblages have been obtained, which are not showing any differences and therefore point to melt compositions close to the feldspar-quartz join. 相似文献
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This article presents a comparison between two two-dimensional finite volume flood propagation models: SRH-2D and Hydro_AS-2D. The models are compared using an experimental dam-break test case provided by Soares-Frazão (J Hydraul Res, 2007. doi: 10.1080/00221686.2007.9521829). Four progressively refined meshes are used, and both models react adequately to mesh and time step refinement. Hydro_AS-2D shows some unphysical oscillations with the finest mesh and a certain loss of accuracy. For that test case, Hydro_AS-2D is more accurate for all meshes and generally faster than SRH-2D. Hydro_AS-2D reacts well to automatic calibration with PEST, whereas SRH-2D has some difficulties in retrieving the suggested Manning’s roughness coefficient. 相似文献
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Two experiments using cylindrical samples of a dolomite-quartz rock were carried out in a conventional hydrothermal apparatus for the forward reaction: 1 dolomite + 2 quartz = 1 diopside + 2 CO2, in order to compare the mechanism and the kinetics with results from experiments using mineral powders of dolomite and quartz at the same P-T-X conditions. Experimental conditions were as follows: total pressure 500 MPa; temperature 680° C (overstepping 65° C); CO2 content of the fluid phase, consisting of carbon dioxide and water, was nearly 90 mol%; the fluid/rock ratio was 1:37, and the H2O/rock ratio was about 1:740; run duration was 92 days. Scanning electron microscope (SEM) examination of a polished axial section of the rock cylinders after the run, using back-scattered electrons (BSE), shows that the reaction produced corona textures. The diopside crystals nucleate and grow exclusively on dolomite surfaces adjacent to quartz grains, i.e. in regions where there is intimate contact between the reactants. The dolomite matrix, in contrast, is diopside free. A concept of microsystems is used to compare directly the rock cylinder results with those from runs done with mineral powders. The microsystems, which consist of quartz, dolomite and diopside, are connected by the intergranular space which is filled by the fluid phase. The SEM analysis of the rock cylinders indicates a dissolution-crystallization mechanism operating in the microsystems; this is consistent with the results of experiments using dolomite quartz powders (Lüttge et al. 1989). It can be demonstrated that reaction kinetics in mineral powder runs are interface controlled as long as the newly formed diopside crystals do not cover the dolomite surfaces completely (Lüttge and Metz 1991 c). This result is applicable to each microsystem of the rock cylinder, since the reaction mechanism and the resulting textures are the same in both kinds of experiments. The reaction is much slower outside the microsystems, i.e. in the dolomite matrix but in the close vicinity of the quartz grains. At these places, the reaction is controlled by the transport of Si-species in the CO2-rich fluid phase filling the intergranular space. The reaction is absent in quartz-free regions of the dolomite matrix. Calculations and measurements of the extent of reaction progress in both kinds of experiments give results of the same order of magnitude: the conversion, and therefore the reaction rate, differs by less than a factor of two. The conclusion is that there are no differences, in principle, concerning mechanisms, rate controls, rates, and resulting textures between rock cylinder experiments, and mineral powder experiments. 相似文献
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《Geochimica et cosmochimica acta》1997,61(24):5279-5293
The Gibbs free energies of formation of RuO 2, OsO 2 and IrO 2 have been determined by measuring the chemical potentials of oxygen (μO 2) defined by the reactions M +O 2 = MO 2,whereM =Ru, Os. or Ir, using an electrochemical method with calcia-stabilized zirconia (CSZ) solid electrolytes. Measurements were attempted in the temperature ranges from ∼870 K to 1620, 1270, and 1415 K for the Ru, Os, and Ir equilibria, respectively, but inspection of the results reveals that equilibrium could not be established below ∼930 K for all three reactions. For Ru + RuO 2, the highest temperature data (above 1520 K) may be systematically affected by the onset of significant electronic conduction in the CSZ electrolyte, while the attempted measurements of the Os + OsO 2 equilibrium above 1190 K are obscured by the disproportionation of OsO 2 to gaseous Os oxides.The high temperature heat capacities at constant pressure (Cp) of RuO 2 and IrO 2 were determined from 370 to 1070 K by differential scanning calorimetry. These data were combined with heat content measurements and low-temperature heat capacities from the literature, and fitted to an extended Maier-Kelley equation. The calorimetric data for RuO 2 and IrO 2, together with assessed data for Ru, Os, and Ir metals and estimated data for OsO 2, were used in a third law analysis of the electrochemical measurements.The values of μO 2 of the three equilibria were smoothed and filtered by the third-law analysis to yield the following equations which can be extrapolated to lower and higher temperatures as indicated: μO 2 (Ru + RuO 2) = −324563 + 344.151 T−22.1155 TlnT (700 ⩽ T ⩽ 1800) μO 2 (Os + OsO 2) = −300399 + 307.639 T−17.4819 TlnT (700 ⩽ T ⩽ 1500) μO 2 (Ir + IrO 2) = −256518 + 295.854 T−15.2368 TlnT (700 ⩽ T ⩽ 1500) where μO 2 is in J mol −1, T is in K, the reference pressure for O 2 is 1 bar (10 5 Pa), and estimated accuracies are approximately 200 to 400 J mol −1. For Ru + RuO 2, the drift in the measurements relative to the calorimetric data deduced from the third-law evaluation is 0.7 J K −1 mol −1, and for Ir + IrO 2 is 1.6 J K −1 mol −1. The analogous third-law evaluation of the Os + OsO 2 data gives S° 298K = 54.8 ± 0.7J K −1mol −1 and Δ /tfH° 298K = −291.8 ± 0.6 kJ mol −1 for OsO 2. 相似文献
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《Applied Geochemistry》2005,20(10):1941-1964
The pH, alkalinity, and acidity of mine drainage and associated waters can be misinterpreted because of the chemical instability of samples and possible misunderstandings of standard analytical method results. Synthetic and field samples of mine drainage having various initial pH values and concentrations of dissolved metals and alkalinity were titrated by several methods, and the results were compared to alkalinity and acidity calculated based on dissolved solutes. The pH, alkalinity, and acidity were compared between fresh, unoxidized and aged, oxidized samples.Data for Pennsylvania coal mine drainage indicates that the pH of fresh samples was predominantly acidic (pH 2.5–4) or near neutral (pH 6–7); ≈ 25% of the samples had pH values between 5 and 6. Following oxidation, no samples had pH values between 5 and 6.The Standard Method Alkalinity titration is constrained to yield values >0. Most calculated and measured alkalinities for samples with positive alkalinities were in close agreement. However, for low-pH samples, the calculated alkalinity can be negative due to negative contributions by dissolved metals that may oxidize and hydrolyze.The Standard Method hot peroxide treatment titration for acidity determination (Hot Acidity) accurately indicates the potential for pH to decrease to acidic values after complete degassing of CO2 and oxidation of Fe and Mn, and it indicates either the excess alkalinity or that required for neutralization of the sample. The Hot Acidity directly measures net acidity (= −net alkalinity). Samples that had near-neutral pH after oxidation had negative Hot Acidity; samples that had pH < 6.3 after oxidation had positive Hot Acidity. Samples with similar pH values before oxidation had dissimilar Hot Acidities due to variations in their alkalinities and dissolved Fe, Mn, and Al concentrations. Hot Acidity was approximately equal to net acidity calculated based on initial pH and dissolved concentrations of Fe, Mn, and Al minus the initial alkalinity. Acidity calculated from the pH and dissolved metals concentrations, assuming equivalents of 2 per mole of Fe and Mn and 3 per mole of Al, was equivalent to that calculated based on complete aqueous speciation of FeII/FeIII. Despite changes in the pH, alkalinity, and metals concentrations, the Hot Acidities were comparable for fresh and most aged samples.A meaningful “net” acidity can be determined from a measured Hot Acidity or by calculation from the pH, alkalinity, and dissolved metals concentrations. The use of net alkalinity = (Alkalinitymeasured − Hot Aciditymeasured) to design mine drainage treatment can lead to systems with insufficient Alkalinity to neutralize metal and H+ acidity and is not recommended. The use of net alkalinity = −Hot Acidity titration is recommended for the planning of mine drainage treatment. The use of net alkalinity = (Alkalinitymeasured − Aciditycalculated) is recommended with some cautions. 相似文献
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A revised equation is proposed to represent and extrapolate the heat capacity of minerals as a function of temperature: C
P=k0+k1
T
–0.5+k2
T
–2+k3
T
–3 (where k1, k20).This equation reproduces calorimetric data within the estimated precision of the measurements, and results in residuals for most minerals that are randomly distributed as a function of temperature. Regression residuals are generally slightly greater than those calculated with the five parameter equation proposed by Haas and Fisher (1976), but are significantly lower than those calculated with the three parameter equation of Maier and Kelley (1932).The revised equation ensures that heat capacity approaches the high temperature limit predicted by lattice vibrational theory (C
P=3R+2VT/). For 16 minerals for which and have been measured, the average C
Pat 3,000 K calculated with the theoretically derived equation ranges from 26.8±0.8 to 29.3±1.9 J/(afu·K) (afu = atoms per formula unit), depending on the assumed temperature dependence of . For 91 minerals for which calorimetric data above 400 K are available, the average C
Pat 3,000 K calculated with our equation is 28.3±2.0 J/(afu·K). This agreement suggests that heat capacity extrapolations should be reliable to considerably higher temperatures than those at which calorimetric data are available, so that thermodynamic calculations can be applied with confidence to a variety of high temperature petrologic problems.Available calorimetric data above 250 K are fit with the revised equation, and derived coefficients are presented for 99 minerals of geologic interest. The heat capacity of other minerals can be estimated (generally within 2%) by summation of tabulated oxide component C
Pcoefficients which were obtained by least squares regression of this data base. 相似文献
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B. Bagautdinov K. Hagiya S. Noguchi M. Ohmasa N. Ikeda K. Kusaka K. Iishi 《Physics and Chemistry of Minerals》2002,29(5):346-350
Two-dimensional modulation in synthetic åkermanite (Ca2MgSi2O7) and hardystonite (Ca2ZnSi2O7) has been studied by the single-crystal X-ray diffraction methods in the temperature range between 18 and 297 K. It is found that change of the modulation wavelength Ca2MgSi2O7 is slight, but that in Ca2ZnSi2O7 it is noticeable and indicates a plateau-like temperature dependence. The plateau-like region may be regarded as an independent phase with a specific q [～0.2924(3)]. 相似文献
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W R Taylor 《Journal of Earth System Science》1990,99(1):99-117
Infrared (IR) and Raman spectroscopic methods are important complementary techniques in structural studies of aluminosilicate glasses. Both techniques are sensitive to small-scale (<15 Å) structural features that amount to units of several SiO4 tetrahedra. Application of IR spectroscopy has, however, been limited by the more complex nature of the IR spectrum compared with the Raman spectrum, particularly at higher frequencies (1200–800 cm?1) where strong antisymmetric Si-O and Si-O-Si absorptions predominate in the former. At lower frequencies, IR spectra contain bands that have substantial contributions from ‘cage-like’ motions of cations in their oxygen co-ordination polyhedra. In aluminosilicates these bands can provide information on the structural environment of Al that is not obtainable directly from Raman studies. A middle frequency envelope centred near 700 cm?1 is indicative of network-substituted AlO4 polyhedra in glasses with Al/(Al+Si)>0·25 and a band at 520–620cm?1 is shown to be associated with AlO6 polyhedra in both crystals and glasses. The IR spectra of melilite and melilite-analogue glasses and crystals show various degrees of band localization that correlate with the extent of Al, Si tetrahedral site ordering. An important conclusion is that differences in Al, Si ordering may lead to very different vibrational spectra in crystals and glasses of otherwise gross chemical similarity. 相似文献
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地球化学在矿产勘查中和地质上的应用可以追溯到20世纪30年代，但“应用地球化学”这一概念的诞生却晚了30年，可从20世纪60年代英国帝国学院建立的“应用地球化学研究组”（Applied Geochemistry Research Group）起算。这一研究组的建立，当时的目的是在英国自然环境研究委员会和农业研究委员会的资助下，将地球化学调查应用于农业和健康。他们做的第一项研究工作就是集中多学科科学家，包括地球化学家、化学家、土壤学家、水文学家、兽医学家和医学家开始对西南英格兰癌症影响因素进行地球化学调查。 相似文献
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Art Boettcher Robert W. Luth Bradford S. White 《Contributions to Mineralogy and Petrology》1987,97(3):297-304
To further our knowledge of the effects of volatile components on phase relationships in aluminosilicate systems, we determined the vapor saturated solidi of albite, anorthite, and sanidine in the presence of CO2 vapor. The depression of the temperature of the solidus of albite by CO2 decreases from 30° C at 10 kbar, to 10° C at 20 kbar, to about 0 at 25 kbar, suggesting that the solubility of CO2 in NaAlSi3O8 liquid in equilibrium with solid albite decreases with increasing pressure and temperature. In contrast, CO2 lowers the temperature of the solidus of anorthite by 30° C at 14 kbar, and by 70dg C at 25 kbar. This contrasting behavior of albite and anorthite is also reflected in the behavior of melting in the absence of volatile components. Whereas albite melts congruently to a liquid of NaAl-Si3O8 composition to pressures of 35 kbar, anorthite melts congruently to only about 10 kbar and, at higher pressures, incongruently to corundum plus a liquid that is enriched in SiO2 and CaO and depleted in Al2O3 relative to CaAl2Si2O8.The tendency toward incongruent melting with increasing pressure in albite and anorthite produces an increase in the activity of SiO2 component in the liquid (
). We predict that this increases the ratio of molecular CO2/CO
3
2–
in these liquids, but the experimental results from other workers are mutually contradictory. Because of the positive dP/dT of the albite solidus and the negative dP/dT of the anorthite solidus, we propose that a negative temperature derivative of the solubility of molecular CO2 in plagioclase liquids may partly explain the decrease in solubility of carbon with increasing pressure in near-solidus NaAlSi3O8 liquids, which is in contrast to that in CaAl2Si2O8 liquid. Also, reaction of CO2 with NaAlSi3O8 liquid to form CO
3
2–
that is complexed with Na+ must be accompanied by a change in Al3+ from network-former to network-modifier, as Na+ is no longer abailable to charge-balance Al3+ in a network-forming role. However, when anorthite melts incongruently to corundum plus a CaO-rich liquid, the complexing of CO
3
2–
with the excess Ca2+ in the liquid does not require a change in the structural role of aluminum, and it may be more energetically favorable.The depression of the temperature of the solidus of sanidine resulting from the addition of CO2 increases from 50° C at 5 kbar to 170° C at 15 kbar. In marked contrast to the plagioclase feldspars, sanidine melts incongruently to leucite plus a SiO2-rich liquid up to the singular point at 15 kbar. Above this pressure, sanidine melts congruently, resulting in a decrease in the
with increasing pressure in the interval up to 15 kbar. Above this pressure, the congruent melting of sanidine results in a lower and nearly constant
relative to those of albite and anorthite, and CO2 produces a nearly constant freezing-point depression of about 170° C. Because of the low
at pressures above the singular point, we infer that most of the carbon dissolves as CO
3
2–
, resulting in a low CO2/ CO
3
2–
, but a high total carbon content.The principles derived from the studies of phase equilibria in these chemically simple systems provide some information on the structural and thermal properties of magmas. We propose that the
is an important parameter in controlling the speciation of carbon in these feldspathic liquids, but it certainly is not the only factor, and it may be relatively less significant in more complex compositions. In addition, our phase-equilibria approach does not provide direct thermal and structural information as do calorimetry and spectroscopy, but the latter have been used primarily on glasses (quenched liquids) and cannot be used in situ to derive direct information on liquids at elevated pressures, as can our method. Hopefully, the results of all of these approaches can be integrated to yield useful results.Institute of Geophysics and Planetary Physics, Contribution No. 2744 相似文献
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The high temperature (β) phases of SiO2 cristobalite and quartz are studied by performing molecular dynamics simulations using a model which allows easy analysis
of tetrahedral motions. The dynamic nature of the disordered high-temperature phase of cristobalite is attributed to rigid
unit mode (RUM) excitations, and it is found that the entire spectrum of RUMs is responsible for the disorder. Comparisons
of the results of β-cristobalite with those of β-quartz lead to the conclusion that framework structures with high degrees
of geometric flexibility, and hence many RUMs, are free to deform through cooperative tetrahedral rotations even in the limit
of extremely large tetrahedral stiffnesses.
Received: 10 March 1998 / Revised, accepted 15 January 1999 相似文献
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Summary The newly developed light sectioning method has been used to investigate some of the causes and costs of overbreak and underbreak. Investigations at the Aquamilpa Hydroelectric Project in Mexico have shown decreased overbreak and increased underbreak as a result of increased rock quality and decreased explosive energy. A new measure of explosive energy, the perimeter powder factor (PPF), has been defined and shown to be useful in the context of tunnel-wall rock damage. Tentative results indicate that explosive energy (PPF) may be a more important factor in producing underbreak, whereas rock quality may be a greater factor in producing overbreak. A site-specific equation is given for predicting overbreak or underbreak as a function of rock quality and explosive energy, with an evaluation of the cost of underbreak and overbreak. 相似文献