首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 46 毫秒
1.
According to the compositions of the underground brine resources in the west of Sichuan Basin, solubilities of the ternary systems NaBr–Na2SO4–H2O and KBr–K2SO4–H2O were investigated by isothermal method at 348 K. The equilibrium solid phases, solubilities of salts, and densities of the solutions were determined. On the basis of the experimental data, the phase diagrams and the density-composition diagrams were plotted. In the two ternary systems, the phase diagrams consist of two univariant curves, one invariant point and two crystallization fields. Neither solid solution nor double salts were found. The equilibrium solid phases in the ternary system NaBr–Na2SO4–H2O are NaBr and Na2SO4, and those in the ternary system KBr–K2SO4–H2O are KBr and K2SO4. Using the solubilities data of the two ternary subsystems at 348 K, mixing ion-interaction parameters of Pitzer’s equation θxxx, Ψxxx and Ψxxx were fitted by multiple linear regression method. Based on the chemical model of Pitzer’s electrolyte solution theory, the solubilities of phase equilibria in the two ternary systems NaBr–Na2SO4–H2O and KBr–K2SO4–H2O were calculated with corresponding parameters. The calculation diagrams were plotted. The results showed that the calculated values have a good agreement with experimental data.  相似文献   

2.
  相似文献   

3.
The solubility of chromium in chlorite as a function of pressure, temperature, and bulk composition was investigated in the system Cr2O3–MgO–Al2O3–SiO2–H2O, and its effect on phase relations evaluated. Three different compositions with X Cr = Cr/(Cr + Al) = 0.075, 0.25, and 0.5 respectively, were investigated at 1.5–6.5 GPa, 650–900 °C. Cr-chlorite only occurs in the bulk composition with X Cr = 0.075; otherwise, spinel and garnet are the major aluminous phases. In the experiments, Cr-chlorite coexists with enstatite up to 3.5 GPa, 800–850 °C, and with forsterite, pyrope, and spinel at higher pressure. At P > 5 GPa other hydrates occur: a Cr-bearing phase-HAPY (Mg2.2Al1.5Cr0.1Si1.1O6(OH)2) is stable in assemblage with pyrope, forsterite, and spinel; Mg-sursassite coexists at 6.0 GPa, 650 °C with forsterite and spinel and a new Cr-bearing phase, named 11.5 Å phase (Mg:Al:Si = 6.3:1.2:2.4) after the first diffraction peak observed in high-resolution X-ray diffraction pattern. Cr affects the stability of chlorite by shifting its breakdown reactions toward higher temperature, but Cr solubility at high pressure is reduced compared with the solubility observed in low-pressure occurrences in hydrothermal environments. Chromium partitions generally according to \(X_{\text{Cr}}^{\text{spinel}}\) ? \(X_{\text{Cr}}^{\text{opx}}\) > \(X_{\text{Cr}}^{\text{chlorite}}\) ≥ \(X_{\text{Cr}}^{\text{HAPY}}\) > \(X_{\text{Cr}}^{\text{garnet}}\). At 5 GPa, 750 °C (bulk with X Cr = 0.075) equilibrium values are \(X_{\text{Cr}}^{\text{spinel}}\) = 0.27, \(X_{\text{Cr}}^{\text{chlorite}}\) = 0.08, \(X_{\text{Cr}}^{\text{garnet}}\) = 0.05; at 5.4 GPa, 720 °C \(X_{\text{Cr}}^{\text{spinel}}\) = 0.33, \(X_{\text{Cr}}^{\text{HAPY}}\) = 0.06, and \(X_{\text{Cr}}^{\text{garnet}}\) = 0.04; and at 3.5 GPa, 850 °C \(X_{\text{Cr}}^{\text{opx}}\) = 0.12 and \(X_{\text{Cr}}^{\text{chlorite}}\) = 0.07. Results on Cr–Al partitioning between spinel and garnet suggest that at low temperature the spinel- to garnet-peridotite transition has a negative slope of 0.5 GPa/100 °C. The formation of phase-HAPY, in assemblage with garnet and spinel, at pressures above chlorite breakdown, provides a viable mechanism to promote H2O transport in metasomatized ultramafic mélanges of subduction channels.  相似文献   

4.
Attikaite, a new mineral species, has been found together with arsenocrandalite, arsenogoyazite, conichalcite, olivenite, philipsbornite, azurite, malachite, carminite, beudantite, goethite, quartz, and allophane at the Christina Mine No. 132, Kamareza, Lavrion District, Attiki Prefecture (Attika), Greece. The mineral is named after the type locality. It forms spheroidal segregations (up to 0.3 mm in diameter) consisting of thin flexible crystals up to 3 × 20 × 80 μm in size. Its color is light blue to greenish blue, with a pale blue streak. The Mohs’ hardness is 2 to 2.5. The cleavage is eminent mica-like parallel to {001}. The density is 3.2(2) g/cm3 (measured in heavy liquids) and 3.356 g/cm3 (calculated). The wave numbers of the absorption bands in the infrared spectrum of attikaite are (cm?1; sh is shoulder; w is a weak band): 3525sh, 3425, 3180, 1642, 1120w, 1070w, 1035w, 900sh, 874, 833, 820, 690w, 645w, 600sh, 555, 486, 458, and 397. Attikaite is optically biaxial, negative, α = 1.642(2), β = γ = 1.644(2) (X = c) 2V means = 10(8)°, and 2V calc = 0°. The new mineral is microscopically colorless and nonpleochroic. The chemical composition (electron microprobe, average over 4 point analyses, wt %) is: 0.17 MgO, 17.48 CaO, 0.12 FeO, 16.28 CuO, 10.61 Al2O3, 0.89 P2O5, 45.45 As2O5, 1.39 SO3, and H2O (by difference) 7.61, where the total is 100.00. The empirical formula calculated on the basis of (O,OH,H2O)22 is: Ca2.94Cu 1.93 2+ Al1.97Mg0.04Fe 0.02 2+ [(As3.74S0.16P0.12)Σ4.02O16.08](OH)3.87 · 2.05H2 O. The simplified formula is Ca3Cu2Al2(AsO4)4(OH)4 · 2H2O. Attikaite is orthorhombic, space group Pban, Pbam or Pba2; the unit-cell dimensions are a = 10.01(1), b = 8.199(5), c = 22.78(1) Å, V = 1870(3) Å3, and Z = 4. In the result of the ignition of attikaite for 30 to 35 min at 128–140°, the H2O bands in the IR spectrum disappear, while the OH-group band is not modified; the weight loss is 4.3%, which approximately corresponds to two H2O molecules per formula; and parameter c decreases from 22.78 to 18.77 Å. The strongest reflections in the X-ray powder diffraction pattern [d, Å (I, %)((hkl)] are: 22.8(100)(001), 11.36(60)(002), 5.01(90)(200), 3.38(5)(123, 205), 2.780(70)(026), 2.682(30)(126), 2.503(50)(400), 2.292(20)(404). The type material of attikaite is deposited in the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow. The registration number is 3435/1.  相似文献   

5.
Experiments at high pressures and temperatures were carried out (1) to investigate the crystal-chemical behaviour of Fe4O5–Mg2Fe2O5 solid solutions and (2) to explore the phase relations involving (Mg,Fe)2Fe2O5 (denoted as O5-phase) and Mg–Fe silicates. Multi-anvil experiments were performed at 11–20 GPa and 1100–1600 °C using different starting compositions including two that were Si-bearing. In Si-free experiments the O5-phase coexists with Fe2O3, hp-(Mg,Fe)Fe2O4, (Mg,Fe)3Fe4O9 or an unquenchable phase of different stoichiometry. Si-bearing experiments yielded phase assemblages consisting of the O5-phase together with olivine, wadsleyite or ringwoodite, majoritic garnet or Fe3+-bearing phase B. However, (Mg,Fe)2Fe2O5 does not incorporate Si. Electron microprobe analyses revealed that phase B incorporates significant amounts of Fe2+ and Fe3+ (at least ~?1.0 cations Fe per formula unit). Fe-L2,3-edge energy-loss near-edge structure spectra confirm the presence of ferric iron [Fe3+/Fetot?=?~?0.41(4)] and indicate substitution according to the following charge-balanced exchange: [4]Si4+?+?[6]Mg2+?=?2Fe3+. The ability to accommodate Fe2+ and Fe3+ makes this potential “water-storing” mineral interesting since such substitutions should enlarge its stability field. The thermodynamic properties of Mg2Fe2O5 have been refined, yielding H°1bar,298?=???1981.5 kJ mol??1. Solid solution is complete across the Fe4O5–Mg2Fe2O5 binary. Molar volume decreases essentially linearly with increasing Mg content, consistent with ideal mixing behaviour. The partitioning of Mg and Fe2+ with silicates indicates that (Mg,Fe)2Fe2O5 has a strong preference for Fe2+. Modelling of partitioning with olivine is consistent with the O5-phase exhibiting ideal mixing behaviour. Mg–Fe2+ partitioning between (Mg,Fe)2Fe2O5 and ringwoodite or wadsleyite is influenced by the presence of Fe3+ and OH incorporation in the silicate phases.  相似文献   

6.
The results of study of phase equilibria in the MgO–SiO2–ZrO2 system at 1450–1550°C are reported. The studied system contains two eutectic points and six fields: (I) MgSiO3 + SiO2; (II) MgSiO3 + ZrO2; (III) ZrSiO4 + SiO2; (IV) MgSiO3 + Mg2SiO4; (V) ZrO2 + MgO; (VI) ZrSiO4 + ZrO2. The presence of fields (II) and (III) on the diagram shows that zircon in equilibrium with olivine and pyroxene crystallizes at very low concentrations of ZrO2 in the system. This provides a solution for one of the most important problems in zirconology of dunites: the probability of the formation and preservation of zircon in the course of the formation and evolution of dunite.  相似文献   

7.
We conducted reversed deliquescence experiments in saturated NaCl–NaNO3–H2O, KNO3–NaNO3–H2O, and NaCl–KNO3–H2O systems from 90 to 120°C as a function of relative humidity and solution composition. NaCl, NaNO3, and KNO3 represent members of dust salt assemblages that are likely to deliquesce and form concentrated brines on high-level radioactive waste package surfaces in a repository environment at Yucca Mountain, NV. Discrepancy between model prediction and experiment can be as high as 8% for relative humidity and 50% for dissolved ion concentration. The discrepancy is attributed primarily to the use of 25°C models for Cl–NO3 and K–NO3 ion interactions in the current Yucca Mountain Project high-temperature Pitzer model to describe the nonideal behavior of these highly concentrated solutions.  相似文献   

8.
To examine the effect of KCl-bearing fluids on the melting behavior of the Earth’s mantle, we conducted experiments in the Mg2SiO4–MgSiO3–H2O and Mg2SiO4–MgSiO3–KCl–H2O systems at 5 GPa. In the Mg2SiO4–MgSiO3–H2O system, the temperature of the fluid-saturated solidus is bracketed between 1,200–1,250°C, and both forsterite and enstatite coexist with the liquid under supersolidus conditions. In the Mg2SiO4–MgSiO3–KCl–H2O systems with molar Cl/(Cl + H2O) ratios of 0.2, 0.4, and 0.6, the temperatures of the fluid-saturated solidus are bracketed between 1,400–1,450°C, 1,550–1,600°C, and 1,600–1,650°C, respectively, and only forsterite coexists with liquid under supersolidus conditions. This increase in the temperature of the solidus demonstrates the significant effect of KCl on reducing the activity of H2O in the fluid in the Mg2SiO4–MgSiO3–H2O system. The change in the melting residues indicates that the incongruent melting of enstatite (enstatite = forsterite + silica-rich melt) could extend to pressures above 5 GPa in KCl-bearing systems, in contrast to the behavior in the KCl-free system.  相似文献   

9.
The influence on the structure of Fe2+ Mg substitution was studied in synthetic single crystals belonging to the MgCr2O4–FeCr2O4 series produced by flux growth at 900–1200 °C in controlled atmosphere. Samples were analyzed by single-crystal X-ray diffraction, electron microprobe analyses, optical absorption-, infrared- and Mössbauer spectroscopy. The Mössbauer data show that iron occurs almost exclusively as IVFe2+. Only minor Fe3+ (<0.005 apfu) was observed in samples with very low total Fe. Optical absorption spectra show that chromium with few exceptions is present as a trivalent cation at the octahedral site. Additional absorption bands attributable to Cr2+ and Cr3+ at the tetrahedral site are evident in spectra of end-member magnesiochromite and solid-solution crystals with low ferrous contents. Structural parameters a0, u and T–O increase with chromite content, while the M–O bond distance remains nearly constant, with an average value equal to 1.995(1) Å corresponding to the Cr3+ octahedral bond distance. The ideal trend between cell parameter, T–O bond length and Fe2+ content (apfu) is described by the following linear relations: a0=8.3325(5) + 0.0443(8)Fe2+ (Å) and T–O=1.9645(6) + 0.033(1)Fe2+ (Å) Consequently, Fe2+ and Mg tetrahedral bond lengths are equal to 1.998(1) Å and 1.965(1) Å, respectively.  相似文献   

10.
Six synthetic NaScSi2O6–CaNiSi2O6 pyroxenes were studied by optical absorption spectroscopy. Five of them of intermediate (Na1−x , Ca x )(Sc1−x , Ni x )Si2O6 compositions show spectra typical of Ni2+ in octahedral coordination, more precise Ni2+ at the M1 site of the pyroxene structure. The common feature of all spectra is three broad absorption bands with maxima around 8,000, 13,000 and 24,000 cm−1 assigned to 3 A 2g → 3 T 2g, 3 A 2g → 3 T 1g and →3 T 1g (3 P) electronic spin-allowed transitions of VINi2+. A weak narrow peak at ∼14,400 cm−1 is assigned to the spin-forbidden 3 A 2g → 1 T 2g (1 D) transition of Ni2+. Under pressure the spin-allowed bands shift to higher energies and change in intensity. The octahedral compression modulus, calculated from the shift of the 3 A 2g → 3 T 2g band in the (Na0.7Ca0.3)(Sc0.7Ni0.3)Si2O6 pyroxene is evaluated as 85±20 GPa. The Racah parameter B of Ni2+(M1) is found gradually changing from ∼919 cm−1 at ambient pressure to ∼890 cm−1 at 6.18 GPa. The Ni end-member pyroxene [(Ca0.93 Ni0.07)NiSi2O6] has a spectrum different from all others. In addition to the above mentioned bands of Ni2+(M1) it displays several new relatively intense and broad extra bands, which were attributed to electronic transitions of Ni2+ at the M2 site. In difference to CaO8 polyhedron geometry of an eightfold coordination, Ni2+(M2)O8 polyhedra are assumed to be relatively large distorted octahedra. Due to different distortions and different compressibilities of the M1 and M2 sites the Ni2+(M1)- and Ni2+(M2)-bands display rather different pressure-induced behaviors, becoming more resolved in the high-pressure spectra than in that measured at atmospheric pressure. The octahedral compression modulus of Ni2+(M1) in this end-member pyroxene is evaluated as 150 ± 25 GPa, which is noticeably larger than in Ni0.3 pyroxene. This is due to a smaller size and, thus, a stiffer character of Ni2+(M1)O6 octahedron in the (Ca0.93Ni0.07)NiSi2O6 pyroxene compared to (Na0.7Ca0.3)(Sc0.7Ni0.3)Si2O6.
Monika Koch-MüllerEmail:
  相似文献   

11.
A new oxygen-deficient perovskite with the composition Ca(Fe0.4Si0.6)O2.8 has been synthesised at high-pressure and -temperature conditions relevant to the Earths transition zone using a multianvil apparatus. In contrast to pure CaSiO3 perovskite, this new phase is quenchable under ambient conditions. The diffraction pattern revealed strong intensities for pseudocubic reflections, but the true lattice is C-centred monoclinic with a=9.2486 Å, b=5.2596 Å, c=21.890 Å and =97.94°. This lattice is only slightly distorted from rhombohedral symmetry. Electron-diffraction and high-resolution TEM images show that a well-ordered ten-layer superstructure is developed along the monoclinic c* direction, which corresponds to the pseudocubic [111] direction. This unique type of superstructure likely consists of an oxygen-deficient double layer with tetrahedrally coordinated silicon, alternating with eight octahedral layers of perovskite structure, which are one half each occupied by silicon and iron as indicated by Mössbauer and Si K electron energy loss spectroscopy. The maximum iron solubility in CaSiO3 perovskite is determined at 16 GPa to be 4 at% on the silicon site and it increases significantly above 20 GPa. The phase relations have been analysed along the join CaSiO3–CaFeO2.5, which revealed that no further defect perovskites are stable. An analogous phase exists in the aluminous system, with Ca(Al0.4Si0.6)O2.8 stoichiometry and diffraction patterns similar to that of Ca(Fe0.4Si0.6)O2.8. In addition, we discovered another defect perovskite with Ca(Al0.5Si0.5)O2.75 stoichiometry and an eight-layer superstructure most likely consisting of a tetrahedral double layer alternating with six octahedral layers. The potential occurrence of all three defect perovskites in the Earths interior is discussed.  相似文献   

12.
Synthesis experiments in the system MgAl2O4–MgFe2O4 [MgAl2–xFexO4 (0 x 2)] were carried out using a PbF2 flux. The crystalline products synthesized in the compositional range of 0.6 <x 1.2 consisted of two spinel phases, whereas those synthesized in the compositional ranges of 0.0 x 0.6 and 1.2 < x 2.0 crystallized as single spinel phases. Structure refinements of the spinel single crystals, which grew in the ranges of 0.0 x 0.6 and 1.2 < x 2.0, show that the degree of randomness of cation distribution between A and B sites increases as x approaches the two-phase region. This means that the degree of the size mismatch among Mg2+, Fe3+ and Al3+occupying each equivalent mixing site increases as x approaches the two-phase region. Consequently, if the coexistence of two spinels observed in the intermediate compositions reveals the existence of a miscibility gap at low temperatures, this increase in the degree of the size mismatch among the three cations is suggested as a factor of energetic destabilization to form the miscibility gap.  相似文献   

13.
Single crystals of C–Na2Si2O5 have been synthesized from the hydrothermal recrystallization of a glass. The title compound is monoclinic, space group P21/c with Z= 8 and unit-cell parameters a= 4.8521 (4)Å, b=23.9793(16)Å, c=8.1410(6)Å, β=90.15(1)° and V=947.2(2)Å3. The structure has been determined by direct methods and belongs to the group of phyllosilicates. It is based on layers of tetrahedra with elliptically six-membered rings in chair conformation. The sequence of directedness within a single ring is UDUDUD. The sheets are parallel to (010) with linking sodium cations in five- and sixfold coordination. Concerning the shape and the conformation of the rings, C–Na2Si2O5 is closely related to β-Na2Si2O5. However, both structures differ in the stacking sequences of the layers. A possible explanation for the frequently observed polysynthetic twinning of phase C is presented. In the 29Si MAS-NMR spectrum of C–Na2Si2O5 four well-resolved lines of equal intensity are observed at ?86.0, ?86.3, ?87.4, and ?88.2?ppm. The narrow range of isotropic chemical shifts reflects the great similarity of the environments of the different Si sites. This lack of pronounced differences in geometry renders a reliable assignment of the resonance lines to the individual sites on the basis of known empiric correlations and geometrical features impossible.  相似文献   

14.
Elastic and thermoelastic constants of large single crystals of Ca2MgSi2O7 and Ca2ZnSi2O7 have been derived from ultrasonic resonance frequencies of plane-parallel plates and their shift upon variation of temperature, respectively. In addition, coefficients of thermal expansion and dielectric constants were determined. Both species possess quite similar properties. As observed in other isotypic magnesium and zinc compounds, the mean elastic stiffness and the deviation from the Cauchy relations are significantly larger in the zinc compound, due to a covalent contribution of the Zn–O bond. Positive thermoelastic constants T44 and T66 in Ca2MgSi2O7 allow temperature-independent ultrasonic generators and oscillators to be manufactured.  相似文献   

15.
In situ high-pressure synchrotron X-ray diffraction and Raman spectroscopic studies of orthorhombic CaFe2O4-type β-CaCr2O4 chromite were carried out up to 16.2 and 32.0 GPa at room temperature using multi-anvil apparatus and diamond anvil cell, respectively. No phase transition was observed in this study. Fitting a third-order Birch–Murnaghan equation of state to the P–V data yields a zero-pressure volume of V 0 = 286.8(1) Å3, an isothermal bulk modulus of K 0 = 183(5) GPa and the first pressure derivative of isothermal bulk modulus K 0′ = 4.1(8). Analyses of axial compressibilities show anisotropic elasticity for β-CaCr2O4 since the a-axis is more compressible than the b- and c-axis. Based on the obtained and previous results, the compressibility of several CaFe2O4-type phases was compared. The high-pressure Raman spectra of β-CaCr2O4 were analyzed to determine the pressure dependences and mode Grüneisen parameters of Raman-active bands. The thermal Grüneisen parameter of β-CaCr2O4 is determined to be 0.93(2), which is smaller than those of CaFe2O4-type CaAl2O4 and MgAl2O4.  相似文献   

16.
Middendorfite, a new mineral species, has been found in a hydrothermal assemblage in Hilairite hyperperalkaline pegmatite at the Kirovsky Mine, Mount Kukisvumchorr apatite deposit, Khibiny alkaline pluton, Kola Peninsula, Russia. Microcline, sodalite, cancrisilite, aegirine, calcite, natrolite, fluorite, narsarsukite, labuntsovite-Mn, mangan-neptunite, and donnayite are associated minerals. Middendorfite occurs as rhombshaped lamellar and tabular crystals up to 0.1 × 0.2 × 0.4 mm in size, which are combined in worm-and fanlike segregations up to 1 mm in size. The color is dark to bright orange, with a yellowish streak and vitreous luster. The mineral is transparent. The cleavage (001) is perfect, micalike; the fracture is scaly; flakes are flexible but not elastic. The Mohs hardness is 3 to 3.5. Density is 2.60 g/cm3 (meas.) and 2.65 g/cm3 (calc.). Middendorfite is biaxial (?), α = 1.534, β = 1.562, and γ = 1.563; 2V (meas.) = 10°. The mineral is pleochroic strongly from yellowish to colorless on X through brown on Y and to deep brown on Z. Optical orientation: X = c. The chemical composition (electron microprobe, H2O determined with Penfield method) is as follows (wt %): 4.55 Na2O, 10.16 K2O, 0.11 CaO, 0.18 MgO, 24.88 MnO, 0.68 FeO, 0.15 ZnO, 0.20 Al2O3, 50.87 SiO2, 0.17 TiO2, 0.23 F, 7.73 H2O; ?O=F2?0.10, total is 99.81. The empirical formula calculated on the basis of (Si,Al)12(O,OH,F)36 is K3.04(Na2.07Ca0.03)Σ2.10(Mn4.95Fe0.13Mg0.06Ti0.03Zn0.03)Σ5.20(Si11.94Al0.06)Σ12O27.57(OH)8.26F0.17 · 1.92H2O. The simplified formula is K3Na2Mn5Si12(O,OH)36 · 2H2O. Middenforite is monoclinic, space group: P21/m or P21. The unit cell dimensions are a = 12.55, b = 5.721, c = 26.86 Å; β = 114.04°, V = 1761 Å3, Z = 2. The strongest lines in the X-ray powder pattern [d, Å, (I)(hkl)] are: 12.28(100)(002), 4.31(81)(11\(\overline 4 \)), 3.555(62)(301, 212), 3.063(52)(008, 31\(\overline 6 \)), 2.840(90)(312, 021, 30\(\overline 9 \)), 2.634(88)(21\(\overline 9 \), 1.0.\(\overline 1 \)0, 12\(\overline 4 \)), 2.366(76)(22\(\overline 6 \), 3.1.\(\overline 1 \)0, 32\(\overline 3 \)), 2.109(54)(42–33, 42–44, 51\(\overline 9 \), 414), 1.669(64)(2.2.\(\overline 1 \)3, 3.2.\(\overline 1 \)3, 62\(\overline 3 \), 6.1.\(\overline 1 \)3), 1.614(56)(5.0.\(\overline 1 \)6, 137, 333, 71\(\overline 1 \)). The infrared spectrum is given. Middendorfite is a phyllosilicate related to bannisterite, parsenttensite, and the minerals of the ganophyllite and stilpnomelane groups. The new mineral is named in memory of A.F. von Middendorff (1815–1894), an outstanding scientist, who carried out the first mineralogical investigations in the Khibiny pluton. The type material of middenforite has been deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow.  相似文献   

17.
The dissolution rate of minerals in silicate melts is generally assumed to be a function of the rate of mass transport of the released cations in the solvent. While this appears to be the case in moderately to highly viscous solvents, there is some evidence that the rate-controlling step may be different in very fluid, highly silica undersaturated melts such as basanites. In this study, convection-free experiments using solvent melts with silica activity from 0.185–0.56 and viscosity from 0.03–4.6 Pa s show that the dissolution rate is strongly dependent on the degree of superheating, silica activity and the viscosity of the solvent. Dissolution rates increase with increasing melt temperature and decreasing silica activity and viscosity. Quartz dissolution in melts with viscosity <0.59–1.9 Pa s and silica activity <0.47 is controlled by the rate of interface reaction as shown by the absence of steady state composition and silica saturation in the interface melts. Only in the most viscous melt with the highest silica activity is quartz dissolution controlled by the rate of diffusion in the melt and only after a long initiation time. The results of this study indicate that although a diffusion-based model may be applicable to dissolution in viscous magmas, a different approach that combines the interplay between the degree of undersaturation of the melt and its viscosity is required in very fluid melts.This revised version was published online September 2004 with a correction to Figure 8.  相似文献   

18.
The paper reports new findings of avdoninite from deposits of active fumaroles in the Second Scoria Cone at the Northern Breach of the Great Fissure Tolbachik Eruption, Tolbachik Volcano, Kamchatka Peninsula, Russia. The crystal structure of the mineral has been determined for the first time, which has allowed reliable determination of its space group and unit cell dimensions, refinement of its formula K2Cu5-Cl8(OH)4 · 2H2O, and correct indexing of its X-ray powder diffraction pattern. Avdoninite is monoclinic, space group P21/c, a = 11.592(2), b = 6.5509(11), c = 11.745(2) Å, β = 91.104(6)°, V = 891.8(3) Å3, Z = 2. The crystal structure of this mineral has been determined on a single crystal R 1 [F > 4σ (F)] = 0.063. It is based on sheets of copper–oxo-chloride complexes [Cu5Cl8(OH)4]2– parallel to (100). The K+ cation and H2O molecules are interlayers.  相似文献   

19.
Kamarizaite, a new mineral species, has been identified in the dump of the Kamariza Mine, Lavrion mining district, Attica Region, Greece, in association with goethite, scorodite, and jarosite. It was named after type locality. Kamarizaite occurs as fine-grained monomineralic aggregates (up to 3 cm across) composed of platy crystals up to 1 μm in size and submicron kidney-shaped segregations. The new mineral is yellow to beige, with light yellow streak. The Mohs hardness is about 3. No cleavage is observed. The density measured by hydrostatic weighing is 3.16(1) g/cm3, and the calculated density is 3.12 g/cm3. The wavenumbers of absorption bands in the IR spectrum of kamarizaite are (cm?1; s is strong band, w is weak band): 3552, 3315s, 3115, 1650w, 1620w, 1089, 911s, 888s, 870, 835s, 808s, 614w, 540, 500, 478, 429. According to TG and IR data, complete dehydration and dehydroxylation in vacuum (with a weight loss of 15.3(1)%) occurs in the temperature range 110–420°C. Mössbauer data indicate that all iron in kamarizaite is octahedrally coordinated Fe3+. Kamarizaite is optically biaxial, positive: n min = 1.825, n max = 1.835, n mean = 1.83(1) (for a fine-grained aggregate). The chemical composition of kamarizaite (electron microprobe, average of four point analyses) is as follows, wt %: 0.35 CaO, 41.78 Fe2O3, 39.89 As2O5, 1.49 SO3, 15.3 H2O (from TG data); the total is 98.81. The empirical formula calculated on the basis of (AsO4,SO4)2 is Ca0.03Fe 2.86 3+ (AsO4)1.90(SO4)0.10(OH)2.74 · 3.27H2O. The idealized formula is Fe 3 3+ (AsO4)2(OH)3 · 3H2O. Kamarizaite is an arsenate analogue of orthorhombic tinticite, space group Pccm, Pcc2, Pcmm, Pcm21, or Pc2m; a = 21.32(1), b = 13.666(6), c =15.80(1) Å, V= 4603.29(5) Å3, Z= 16. The strongest reflections of the X-ray powder diffraction pattern [\(\bar d\), Å (I, %) (hkl)] are: 6.61 (37) (112, 120), 5.85 (52) (311), 3.947 (100) (004, 032, 511), 3.396 (37) (133, 431), 3.332 (60) (314), 3.085 (58) (621, 414, 324). The type material of kamarizaite is deposited in the Mineralogical Collection of Technische Universität Bergakademie Freiberg, Germany, inventory number 82199.  相似文献   

20.
Reactions and partial melting of peraluminous rocks in the presence of H2O-CO2–salt fluids under parameters of granulite-facies metamorphism were modeled in experiments on interaction between orthopyroxene–cordierite–biotite–plagioclase–quartz metapelite with H2O, H2O-CO2, H2O-CO2-NaCl, and H2O-CO2-KCl fluids at 600 MPa and 850°C. Rock melting in the presence of H2O and equimolar H2O-CO2 fluids generates peraluminous (A/CNK1 > 1.1) melts whose composition corresponds to magnesian calcic or calc–alkaline S-type granitoids. The melts are associated with peritectic phases: magnesian spinel and orthopyroxene containing up to 9 wt % Al2O3. In the presence of H2O-CO2-NaCl fluid, cordierite and orthopyroxene are replaced by the association of K-Na biotite, Na-bearing gedrite, spinel, and albite. The Na2O concentrations in the biotite and gedrite are functions of the NaCl concentrations in the starting fluid. Fluids of the composition H2O-CO2-KCl induce cordierite replacement by biotite with corundum and spinel and by these phases in association with potassium feldspar at X KCl = 0.02 in the fluid. When replaced by these phases, cordierite is excluded from the melting reactions, and the overall melting of the metapelite is controlled by peritectic reactions of biotite and orthopyroxene with plagioclase and quartz. These reactions produce such minerals atypical of metapelites as Ca-Na amphibole and clinopyroxene. The compositions of melts derived in the presence of salt-bearing fluids are shifted toward the region with A/CNK < 1.1, as is typical of so-called peraluminous granites of type I. An increase in the concentrations of salts in the fluids leads to depletion of the melts in Al2O3 and CaO and enrichment in alkalis. These relations suggest that the protoliths of I-type peraluminous granites might have been metapelites that were melted when interacting with H2O-CO2-salt fluids. The compositions of the melts can evolve from those with A/CNK > 1.1 (typical of S-type granites) toward those with A/CNK = 1.0–1.1 in response to an increase in the concentrations of alkali salts in the fluids within a few mole percent. Our experiments demonstrate that the origin of new mineral assemblages in metapelite in equilibrium with H2O-CO2-salt fluids is controlled by the activities of alkaline components, while the H2O and CO2 activities play subordinate roles. This conclusion is consistent with the results obtained by simulating metapelite mineral assemblages by Gibbs free energy minimization (using the PERPE_X software), as shown in log(\({a_{{H_2}O}}\))–log(\({a_{N{a_2}O}}\)) and log(\({a_{{H_2}O}}\))–log(\({a_{{K_2}O}}\)) diagrams.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号