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1.
The spinel solid solution was found to exist in the whole range between Fe3O4 and γ-Fe2SiO4 at over 10 GPa. The resistivity of Fe3−
x
Si
x
O4 (0.0<x<0.288) was measured in the temperature range of 80∼300 K by the AC impedance method. Electron hopping between Fe3+ and Fe2+ in the octahedral site of iron-rich phases gives a large electric conductivity at room temperature. The activation energy
of the electron hopping becomes larger with increasing γ-Fe2SiO4 component. A nonlinear change in electric conductivity is not simply caused by the statistical probability of Fe3+–Fe2+ electron hopping with increasing the total Si content. This is probably because a large number of Si4+ ions occupies the octahedral site and the adjacent Fe2+ keeping the local electric neutrality around Si4+ makes a cluster, which generates a local deformation by Si substitution.
The temperature dependence of the conductivity of solid solutions indicates the Verwey transition temperature, which decreases
from 124(±2) K at x=0 (Fe3O4) to 102(±5) K at x=0.288, and the electric conductivity gap at the transition temperature decreases with Si4+ substitution.
Received: 15 March 2000 / Accepted: 4 September 2000 相似文献
2.
P. A. van Aken V. J. Styrsa B. Liebscher A. B. Woodland G. J. Redhammer 《Physics and Chemistry of Minerals》1999,26(7):584-590
The Fe M
2,3-edge spectra of solid solutions of garnets (almandine-skiagite Fe3(Al1–xFex)2[SiO4]3 and andradite-skiagite (Fe1–xCax)3Fe2[SiO4]3), pyroxenes (acmite-hedenbergite (Ca1–xNax)(Fe2+
1−xFe3+
x)Si2O6), and spinels (magnetite-hercynite Fe(Al1–xFex)2O4) have been measured using the technique of parallel electron energy-loss spectroscopy (EELS) conducted in a transmission
electron microscope (TEM). The Fe M
2,3 electron energy-loss near-edge structures (ELNES) of the minerals exhibit a characteristic peak located at 4.2 eV and 2.2 eV
for trivalent and divalent iron, respectively, prior to the main maximum at about 57 eV. The intensity and energy of the pre-edge
feature varies depending on Fe3+/ΣFe. We demonstrate a new quantitative method to extract the ferrous/ferric ratio in minerals. A systematic relationship
between Fe3+/ΣFe and the integral intensity ratio of the main maximum and the pre-edge peak of the Fe M
2,3 edge is observed. Since the partial cross sections of the Fe M
2,3 edges are some orders of magnitude higher than those of the Fe L
2,3 edges, the Fe M
2,3 edges are interesting for valence-specific imaging of Fe. The possibility of iron valence-specific imaging is illustrated
by Fe M
2,3-ELNES investigations with high lateral resolution from a sample of ilmenite containing hematite exsolution lamellae that
shows different edge shapes consistent with variations in the Fe3+/ΣFe ratio over distances on the order of 100 nm.
Received: 14 April 1998 / Revised, accepted: 8 March 1999 相似文献
3.
The structural behavior of stuffed derivatives of quartz within the Li1−
x
Al1−
x
Si1+
x
O4 system (0 ≤ x ≤ 1) has been studied in the temperature range 20 to 873 K using high-resolution powder synchrotron X-ray diffraction (XRD).
Rietveld analysis reveals three distinct regimes whose boundaries are defined by an Al/Si order-disorder transition at x=∼0.3 and a β–α displacive transformation at x=∼0.65. Compounds that are topologically identical to β-quartz (0 ≤ x < ∼0.65) expand within the (0 0 1) plane and contract along c with increasing temperature; however, this thermal anisotropy is significantly higher for structures within the regime 0 ≤ x < ∼0.3 than for those with compositions ∼0.3 ≤ x < ∼0.65. We attribute this disparity to a tetrahedral tilting mechanism that occurs only in the ordered structures (0 ≤ x < ∼0.3). The phases with ∼0.65 ≤ x ≤ 1 adopt the α-quartz structure at room temperature, and they display positive thermal expansion along both a and c from 20 K to their α–β transition temperatures. This behavior arises mainly from a rotation of rigid Si(Al)-tetrahedra about
the <100> axes. Landau analysis provides quantitative evidence that the charge-coupled substitution of Li+Al for Si in quartz
dampens the α–β transition. With increasing Li+Al content, the low-temperature modifications exhibit a marked decrease in
spontaneous strain; this behavior reflects a weakening of the first-order character of the transition. In addition, we observe
a linear decrease in the α–β critical temperature from 846 K to near 0 K as the Li+Al content increases from x=0 to x=∼0.5.
Received: 26 June 2000 / Accepted: 1 December 2000 相似文献
4.
The crystal structure of Bi2Al4−x
Fe
x
O9 compounds (x = 0–4) has striking similarities with the crystal structure of mullite. A complete substitution of Al by Fe3+ in both octahedral and tetrahedral sites is a particular structural feature. The infrared (IR) spectra of the Bi2M4O9 compounds (M = Al, Fe3+) are characterised by three band groups with band maxima in the 900–800, 800–600 and 600–400 cm−1 region. Based on the spectroscopic results obtained from mullite-type phases, the present study focuses on the composition-dependent analysis of the 900–800 cm−1 band group, which is assigned to Al(Fe3+)–O stretching vibrations of the corner-sharing MO4 tetrahedra. The Bi2Al4O9 and Bi2Fe4O9 endmembers display single bands with maxima centred at 922 and 812 cm−1, respectively. Intermediate Bi2Al4−x
Fe
x
O9 compounds exhibit a distinct splitting into three relatively sharp bands, which is interpreted in terms of ordering effects within the tetrahedral pairs. Thereby the high-energy component band of the band triplet relates to Al–O–Al conjunctions and the low-energy component band to Fe–O–Fe conjunctions. The intermediate band is assigned to stretching vibrations of Al–O–Fe or Fe–O–Al configurations of the corner-sharing tetrahedral pairs. Bands in the 800–600 cm−1 range are assigned to low-energy stretching vibrations of the MO4 tetrahedra and to M–O–M bending vibrations of the tetrahedral pairs. Absorptions in the 600–400 cm−1 range are essentially determined by M–O stretching modes of the M cations in octahedral coordination. 相似文献
5.
A. Mücke 《Mineralogy and Petrology》2003,77(3-4):215-234
Summary ?Detailed petrographic studies and microchemical analyses of titanomagnetite from igneous and metamorphic rocks and ore deposits
form the basis of this investigation. Its aim is to compare the data obtained and their interpretations with the experimentally
deduced subsolidus oxidation-exsolution model of Buddington and Lindsley (1964). The results are also considered relevant for the interpretation of compositional variations in black sands which
are recovered for titanium production. The arrangement of the samples investigated is in accordance with textural stages C1
to C5 caused by subsolidus exsolution with increasing degrees of oxidation (Haggerty, 1991).
Stage 1 is represented by two types of optically homogeneous TiO2-rich magnetite: a. An isotropic type considered to represent solid solutions of magnetite and ulvite containing between 5.2
to 27.5 wt% TiO2 corresponding to about 14.7 to 77.7 mol% Fe2TiO4 in solid solution with magnetite. The general formula of this type is Fe2+
1+x
Fe3+
2−2x
Ti
x
O4 (x = 0.0–1.0). b. The second type which has not been reported so far is anisotropic and shows complex internal twinning resembling
inversion textures. It is thus attributed to inversion of a high-temperature ilmenite modification (with statistical distribution
of the cations) which forms solid solutions with magnetite. TiO2 varies between 9.3 and 24.5 wt% corresponding to about 17.2 to 43.6 mol% ilmenite in solid solution with magnetite. This
type is interpreted as a cation-deficient spinel with the general formula Fe2+
12/12 + 1/4xFe3+
24/12 − 3/2x
□
0 + 1/4x
Ti
x
O4 (x = 0.0–16/12). Isotropic and anisotropic homogeneous magnetites occur in volcanic rocks only; the homogeneity of the solid
solutions was explained by fast cooling which prevented the development of exsolution textures.
Stages 2 and 3 are represented by magnetite with or without ulvite. The magnetite host contains ilmenite lamellae forming
trellis and sandwich textures. In contrast to the requirement of the oxidation-exsolution model, the ilmenite lamellae are
concentrated exclusively in the cores of the host crystals. The reverse host-guest relationship may also occur. Stages 4 and
5 are identical with thermally generated martite (= martite due to heating). The textures are characterized by very broad
lamellae of ferrian ilmenite or titanohematite dominantly concentrated along the margins of the host crystals. Thermally generated
martite is restricted to subsolidus-oxidation reactions.
The ilmenite lamellae of trellis and sandwich textures contain low Fe2O3-concentrations (average 4.8 mol%; to a maximum of 8.3), whereas the Fe2O3-content of thermally generated martite is between 32 to 71 mol%. With respect to the Fe2O3-concentrations in the ilmenite lamellae, no transition between the two types was observed.
The results of this paper show that the widely accepted oxy-exsolution model of Buddington and Lindsley (1964) which is based on experimental results can – with the exception of thermally generated martite – not explain the tremendous
variety of magnetite–ilmenite–ulvite relationships in natural rocks and ore deposits.
Received October 16, 2001; accepted May 2, 2002 相似文献
6.
K.-D. Grevel A. Navrotsky W. A. Kahl D. W. Fasshauer J. Majzlan 《Physics and Chemistry of Minerals》2001,28(7):475-487
Calorimetric and P–V–T data for the high-pressure phase Mg5Al5Si6O21(OH)7 (Mg-sursassite) have been obtained. The enthalpy of drop solution of three different samples was measured by high-temperature
oxide melt calorimetry in two laboratories (UC Davis, California, and Ruhr University Bochum, Germany) using lead borate (2PbO·B2O3) at T=700 ∘C as solvent. The resulting values were used to calculate the enthalpy of formation from different thermodynamic datasets;
they range from −221.1 to −259.4 kJ mol−1 (formation from the oxides) respectively −13892.2 to −13927.9 kJ mol−1 (formation from the elements). The heat capacity of Mg5Al5Si6O21(OH)7 has been measured from T=50 ∘C to T=500 ∘C by differential scanning calorimetry in step-scanning mode. A Berman and Brown (1985)-type four-term equation represents
the heat capacity over the entire temperature range to within the experimental uncertainty: C
P
(Mg-sursassite) =(1571.104 −10560.89×T
−0.5−26217890.0 ×T
−2+1798861000.0×T
−3) J K−1 mol−1 (T in K). The P
V
T behaviour of Mg-sursassite has been determined under high pressures and high temperatures up to 8 GPa and 800 ∘C using a MAX 80 cubic anvil high-pressure apparatus. The samples were mixed with Vaseline to ensure hydrostatic pressure-transmitting
conditions, NaCl served as an internal standard for pressure calibration. By fitting a Birch-Murnaghan EOS to the data, the
bulk modulus was determined as 116.0±1.3 GPa, (K
′=4), V
T,0
=446.49 3 exp[∫(0.33±0.05) × 10−4 + (0.65±0.85)×10−8
T dT], (K
T/T)
P
= −0.011± 0.004 GPa K−1. The thermodynamic data obtained for Mg-sursassite are consistent with phase equilibrium data reported recently (Fockenberg
1998); the best agreement was obtained with Δf
H
0
298 (Mg-sursassite) = −13901.33 kJ mol−1, and S
0
298 (Mg-sursassite) = 614.61 J K−1 mol−1.
Received: 21 September 2000 / Accepted: 26 February 2001 相似文献
7.
The structural behavior of synthetic gahnite (ZnAl2O4) has been investigated by X-ray powder diffraction at high pressure (0–43 GPa) and room temperature, on the ID9 beamline
at ESRF. The equation of state of gahnite has been derived using the models of Birch–Murnaghan, Vinet and Poirier–Tarantola,
and the results have been mutually compared (the elastic bulk modulus and its derivatives versus P determined by the third-order Birch–Murnaghan equation of state are K
0=201.7(±0.9) GPa, K
′
0=7.62(±0.09) and K
″
0=−0.1022 GPa−1 (implied value). The compressibilities of the tetrahedral and octahedral bond lengths [0.00188(8) and 0.00142(5) GPa−1 at P=0, respectively], and the␣polyhedral volume compressibilities of the four-␣and␣sixfold coordination sites [0.0057(2) and
0.0041(2) GPa−1 at P=0, respectively] are discussed.
Received: 15 January 2001 / Accepted: 23 April 2001 相似文献
8.
Structural parameters and cation ordering are determined for four compositions in the synthetic MgGa2O4-Mg2GeO4 spinel solid solution (0, 8, 15 and 23 mol% Mg2GeO4; 1400 °C, 1 bar) and for spinelloid β-Mg3Ga2GeO8 (1350 °C, 1 bar), by Rietveld refinement of room-temperature neutron diffraction data. Sample chemistry is determined by
XRF and EPMA. Addition of Mg2GeO4 causes the cation distribution of the MgGa2O4 component to change from a disordered inverse distribution in end member MgGa2O4, [4]Ga = x = 0.88(3), through the random distribution, toward a normal cation distribution, x = 0.37(3), at 23 mol% Mg2GeO4. An increase in ao with increasing Mg2GeO4 component is correlated with an increase in the amount of Mg on the tetrahedral site, through substitution of 2 Ga3+⇄ Mg2++Ge4+. The spinel exhibits high configurational entropy, reaching 20.2 J mol−1 (four oxygen basis) near the compositional upper limit of the solid solution. This stabilizes the spinel in spite of positive
enthalpy of disordering over the solid solution, where ΔH
D
= αx + βx
2, α = 22(3), β = −21(3) kJ mol−1. This model for the cation distribution across the join suggests that the empirically determined limit of the spinel solid
solution is correlated with the limit of tetrahedral ordering of Mg, after which local charge-balanced substitution is no
longer maintained.
Spinelloid β-Mg3Ga2GeO8 has cation distribution M1[Mg0.50(2)Ga0.50(2)] M2[Mg0.96(2)Ga0.04(2)] M3[Mg0.77(2) Ga0.23(2)]2 (Ge0.5Ga0.5)2O8 (tetrahedral site occupancies are assumed). Octahedral site size is correlated to Mg distribution, where site volume, site
distortion, and Mg content follow the relation M1<M3<M2. The disordered cation distribution provides local electrical neutrality
in the structure, and stabilization through increased configurational entropy (27.6 J mol−1; eight oxygen basis). Comparison of the crystal structures of Mg1+
N
Ga2−2
N
Ge
N
O4 spinel, β-Mg3Ga2GeO8, and Mg2GeO4 olivine reveals β-Mg3Ga2GeO8 to be a true structural intermediate. Phase transitions across the pseudobinary are necessary to accommodate an increasing
divergence of cation size and valence, with addition of Mg2GeO4 component. Octahedral volume increases while tetrahedral volume decreases from spinel to β-Mg3Ga2GeO8 to olivine, with addition of Mg and Ge, respectively. Furthermore, M-M distances increase regularly across the join, suggesting
that changes in topology reduce cation-cation repulsion.
Received: 9 November 1998 / Revised, accepted: 3 August 1999 相似文献
9.
Frédéric Hatert André-Mathieu Fransolet Walter V. Maresch 《Contributions to Mineralogy and Petrology》2006,152(4):399-419
In order to assess the geothermometric potential of the Na2(Mn2−2x
Fe1+2x
)(PO4)3 system (x = 0–1), which represents the compositions of natural weakly oxidized alluaudites, we performed hydrothermal experiments between 400 and 800°C, at 1 kbar, under an oxygen fugacity (f(O2)) controlled by the Ni–NiO (NNO), Fe2O3–Fe3O4 (HM), Cu2O–CuO (CT), and Fe–Fe3O4 (MI) buffers. When f(O2) is controlled by NNO, single-phase alluaudites crystallize at 400 and 500°C, whereas the association alluaudite + marićite appears between 500 and 700°C. The limit between these two fields corresponds to the maximum temperature that can be reached by alluaudites in granitic pegmatites, because marićite has never been observed in these geological environments. Because alluaudites are very sensitive to variations of oxygen fugacity, the field of hagendorfite, Na2MnFe2+Fe3+(PO4)3, has been positioned in the f(O2)–T diagram, and provides a tool that can be used to estimate the oxygen fugacity conditions that prevailed in granitic pegmatites during the crystallization of this phosphate. 相似文献
10.
Enthalpies of drop solution (ΔH
drop-sol) of CaGeO3, Ca(Si0.1Ge0.9)O3, Ca(Si0.2Ge0.8)O3, Ca(Si0.3Ge0.7)O3 perovskite solid solutions and CaSiO3 wollastonite were measured by high-temperature calorimetry using molten 2PbO · B2O3 solvent at 974 K. The obtained values were extrapolated linearly to the CaSiO3 end member to give ΔH
drop-sol of CaSiO3 perovskite of 0.2 ± 4.4 kJ mol−1. The difference in ΔH
drop-sol between CaSiO3, wollastonite, and perovskite gives a transformation enthalpy (wo → pv) of 104.4 ± 4.4 kJ mol−1. The formation enthalpy of CaSiO3 perovskite was determined as 14.8 ± 4.4 kJ mol−1 from lime + quartz or −22.2 ± 4.5 kJ mol−1 from lime + stishovite. A comparison of lattice energies among A2+B4+O3 perovskites suggests that amorphization during decompression may be due to the destabilizing effect on CaSiO3 perovskite from a large nonelectrostatic energy (repulsion energy) at atmospheric pressure. By using the formation enthalpy
for CaSiO3 perovskite, phase boundaries between β-Ca2SiO4 + CaSi2O5 and CaSiO3 perovskite were calculated thermodynamically utilizing two different reference points [where ΔG(P,T )=0] as the measured phase boundary. The calculations suggest that the phase equilibrium boundary occurs between 11.5 and
12.5 GPa around 1500 K. Its slope is still not well constrained.
Received: 20 September 2000 / Accepted: 17 January 2001 相似文献
11.
Jian-Wei Li Xin-Fu Zhao Mei-Fu Zhou Paulo Vasconcelos Chang-Qian Ma Xiao-Dong Deng Zorano Sérgio de Souza Yong-Xin Zhao Gang Wu 《Mineralium Deposita》2008,43(3):315-336
The Tongshankou Cu–Mo deposit, located in the westernmost Daye district of the Late Mesozoic Metallogenic Belt along the Middle-Lower
reaches of the Yangtze River, eastern China, consists mainly of porphyry and skarn ores hosted in the Tongshankou granodiorite
and along the contact with the Lower Triassic marine carbonates, respectively. Sensitive high-resolution ion microprobe zircon
U–Pb dating constrains the crystallization of the granodiorite at 140.6 ± 2.4 Ma (1σ). Six molybdenite samples from the porphyry ores yield Re–Os isochron age of 143.8 ± 2.6 Ma (2σ), while a phlogopite sample from the skarn ores yields an 40Ar/39Ar plateau age of 143.0 ± 0.3 Ma and an isochron age of 143.8 ± 0.8 Ma (2σ), indicating an earliest Cretaceous mineralization event. The Tongshankou granodiorite has geochemical features resembling
slab-derived adakites, such as high Sr (740–1,300 ppm) and enrichment in light rare earth elements (REE), low Sc (<10 ppm),
Y (<13.3 ppm), and depletion in heavy REE (<1.2 ppm Yb), and resultant high Sr/Y (60–92) and La/Yb (26–75) ratios. However,
they differ from typical subduction-related adakites by high K, low MgO and Mg#, and radiogenic Sr–Nd–Hf isotopic compositions,
with (87Sr/86Sr)
t
= 0.7062–0.7067, ɛ
Nd(t) = −4.37 to −4.63, (176Hf/177Hf)
t
= 0.282469–0.282590, and ɛ
Hf(t) = −3.3 to −7.6. The geochemical and isotopic data, coupled with geological analysis, indicate that the Tongshankou granodiorite
was most likely generated by partial melting of enriched lithospheric mantle that was previously metasomitized by slab melts
related to an ancient subduction system. Magmas derived from such a source could have acquired a high oxidation state, as
indicated by the assemblage of quartz–magnetite–titanite–amphibole–Mg-rich biotite in the Tongshankou granodiorite and the
compositions of magmatic biotite that fall in the field between the NiNiO and magnetite–hematite buffers in the Fe3+–Fe2+–Mg diagram. Sulfur would have been present as sulfates in such highly oxidized magmas, so that chalcophile elements Cu and
Mo were retained as incompatible elements in the melt, contributing to subsequent mineralization. A compilation of existing
data reveals that porphyry and porphyry-related Cu–Fe–Au–Mo mineralization from Daye and other districts of the Metallogenic
Belt along the Middle-Lower reaches of the Yangtze River took place coevally in the Early Cretaceous and was related to an
intracontinental extensional environment, distinctly different from the arc-compressive setting of the Cenozoic age that has
been responsible for the emplacement of most porphyry Cu deposits of the Pacific Rim. 相似文献
12.
The variation of the oxygen content in olivines, (Fe
x
Mg1−
x
)2SiO4, with 0.2 ≤ x ≤ 1.0, was investigated by thermogravimetric measurements. Mass changes occurring upon oxygen activity changes were measured
as a function of oxygen activity and cationic composition at 1130 and 1200 °C. During the measurements the samples were in
direct contact with gases containing CO, CO2 and N2 and, at a few spots at the bottom of the sample stack, also with SiO2. By fitting experimental data of mass changes to equations derived using point defect thermodynamics, it was shown for olivines
with 0.2 ≤ x ≤ 1.0 at 1130 °C and 0.2 ≤ x ≤ 0.7 at 1200 °C within the oxygen activity ranges investigated that the observed variations in the oxygen contents are compatible
with cation vacancies and Fe3+ ions on M sites and Fe3+ ions on silicon sites as majority defects if it is assumed that only three types of point defects occur as majority defects.
Different cases were considered, closed systems, taking into account that ξ=[Si]/([Si]+[Fe]+[Mg]) is not necessarily equal
to 1/3, and olivines in equilibrium with SiO2 or pyroxenes. The oxygen content variations observed in this study are significantly smaller than those reported previously
in the literature. It is proposed that these differences are related to the dissolution of Fe into noble metal containers
used as sample holders in earlier studies and/or to the presence of secondary phases.
Received: 1 November 1995 / Accepted: 15 September 2002
Acknowledgements This work was supported by the Cornell Center for Materials Research (CCMR), a Materials Research Science and Engineering
Center of the National Science Foundation (DMR-0079992). The authors thank Mr. Daniel M. DiPasquo and Mr. Jason A. Schick
for helping in experimental work. 相似文献
13.
N. V. Zubkova D. Yu. Pushcharovsky G. Giester E. Tillmanns I. V. Pekov D. A. Kleimenov 《Mineralogy and Petrology》2002,75(1-2):79-88
Summary
The crystal structure of arsentsumebite, ideally, Pb2Cu[(As, S)O4]2(OH), monoclinic, space group P21/m, a = 7.804(8), b = 5.890(6), c = 8.964(8) ?, β = 112.29(6)°, V = 381.2 ?3, Z = 2, dcalc. = 6.481 has been refined to R = 0.053 for 898 unique reflections with I> 2σ(I). Arsentsumebite belongs to the brackebuschite group of lead minerals with the general formula Pb2
Me(XO4)2(Z) where Me = Cu2+, Mn2+, Zn2+, Fe2+, Fe3+; X = S, Cr, V, As, P; Z = OH, H2O. Members of this group include tsumebite, Pb2Cu(SO4)(PO4)(OH), vauquelinite, Pb2Cu(CrO4)(PO4)(OH), brackebuschite, Pb2 (Mn, Fe)(VO4)2(OH), arsenbracke buschite, Pb2(Fe, Zn)(AsO4)2(OH, H2O), fornacite, Pb2Cu(AsO4)(CrO4)(OH), and feinglosite, Pb2(Zn, Fe)[(As, S)O4]2(H2O). Arsentsumebite and all other group members contain M = M–T chains where M = M means edge-sharing between MO6 octahedra and M–T represents corner sharing between octahedra and XO4 tetrahedra. A structural relationship exists to tsumcorite, Pb(Zn, Fe)2(AsO4)2 (OH, H2O)2 and tsumcorite-group minerals Me(1)Me(2)2(XO4)2(OH, H2O)2.
Received June 24, 2000; revised version accepted February 8, 2001 相似文献
14.
Amphiboles were synthesized from bulk compositions prepared along the join Ca1.8Mg5.2Si8O22(OH)2–Ca1.8Mg3Ga4Si6O22(OH)2 hydrothermally at 750–850 °C and 1.0–1.8 GPa, and along the join Ca2Mg5Si8O22F2–Ca2Mg3Ga4Si6O22F2, anhydrously at 1000 °C and 0.7 GPa to document how closely the tschermak-type substitution is obeyed in these analogues
of aluminous amphiboles. Electron-microprobe analyses and Rietveld X-ray diffraction structure refinements were performed
to determine cation site occupancies. The extent of Ga substitution was found to be limited in both joins, but with the fluorine
series having about twice the Ga content (0.6 atoms per formula unit, apfu) of the hydroxyl-series amphiboles (0.3 apfu).
The tschermak-type substitution was followed very closely in the hydroxyl series with essentially equal partitioning of Ga
between tetrahedral and octahedral sites. The fluorine-series amphiboles deviated significantly from the tschermak-type substitution
and, instead, appeared to follow a substitution that is close to a Ca-pargasite substitution of the type: [6]Ga3++2[4]Ga3++1/2[A] Ca2+ = [6]Mg2++2[4]Si4++1/2[A]□. Infrared spectroscopy revealed an inverse correlation between the intensity of the OH-stretching bands and the Ga content
for the hydroxyl- and fluorine-series amphiboles. The direct correlation between the Ga and F content and inverse relationship between the Ga and
OH content may be a general phenomenon present in other minerals and suggests, for example, that high F contents in titanite
are controlled by the Al content of the host rock and that there may be similar direct Al–F correlations in tschermakitic
amphiboles. Evidence for the possibility that Al (Ga) might substitute onto only a subset of the tetrahedral sites in tschermakitic
amphiboles was sought but not observed in this study.
Received: 5 March 2001 / Accepted: 31 July 2001 相似文献
15.
The lattice constants of paragonite-2M1, NaAl2(AlSi3)O10(OH)2, were determined to 800 °C by the single-crystal diffraction method. Mean thermal expansion coefficients, in the range 25–600 °C,
were: αa = 1.51(8) × 10−5, αb = 1.94(6) × 10−5, αc = 2.15(7) × 10−5 °C−1, and αV = 5.9(2) × 10−5 °C−1. At T higher than 600 °C, cell parameters showed a change in expansion rate due to a dehydroxylation process. The structural refinements
of natural paragonite, carried out at 25, 210, 450 and 600 °C, before dehydroxylation, showed that the larger thermal expansion
along the c parameter was mainly due to interlayer thickness dilatation. In the 25–600 °C range, Si,Al tetrahedra remained quite unchanged,
whereas the other polyhedra expanded linearly with expansion rate proportional to their volume. The polyhedron around the
interlayer cation Na became more regular with temperature. Tetrahedral rotation angle α changed from 16.2 to 12.9°. The structure
of the new phase, nominally NaAl2 (AlSi3)O11, obtained as a consequence of dehydroxylation, had a cell volume 4.2% larger than that of paragonite. It was refined at room
temperature and its expansion coefficients determined in the range 25–800 °C. The most significant structural difference from
paragonite was the presence of Al in fivefold coordination, according to a distorted trigonal bipyramid. Results confirm the
structural effects of the dehydration mechanism of micas and dioctahedral 2:1 layer silicates. By combining thermal expansion
and compressibility data, the following approximate equation of state in the PTV space was obtained for paragonite: V/V
0 = 1 + 5.9(2) × 10−5
T(°C) − 0.00153(4) P(kbar).
Received: 12 July 1999 / Revised, accepted: 7 December 1999 相似文献
16.
The partitioning of Mg and Fe between magnesiowüstite and ringwoodite solid solutions has been measured between 15 and 23 GPa
and 1200–1600 ∘C using both Fe and Re capsule materials to vary the oxidation conditions. The partitioning results show a clear dependence
on the capsule material used due to the variation in Fe3+ concentrations as a consequence of the different oxidation environments. Using results from experiments performed in Fe capsules,
where metallic Fe was also added to the starting materials, the difference in the interaction parameters for the two solid
solutions (W
FeMg
mw−W
FeMg
ring) is calculated to be 8.5±1 kJ mol−1. Similar experiments performed in Re metal capsules result in a value for W
FeMg
mw−W
FeMg
ring that is apparently 4 kJ higher, if all Fe is assumed to be FeO. Electron energy-loss near-edge structure (ELNES) spectroscopic
analyses, however, show Fe3+ concentrations to be approximately three times higher in magnesiowüstite produced in Re capsules than in Fe capsules and
that Fe3+ partitions preferentially into magnesiowüstite, with K
D
Fe3+
ring/mw estimated between 0.1 and 0.6. Using an existing activity composition model for magnesiowüstite, a least–squares fit to the
partitioning data collected in Fe capsules results in a value for the ringwoodite interaction parameter (W
FeMg
ring) of 3.5±1 kJ mol−1. The equivalent regular interaction parameter for magnesiowüstite (W
FeMg
mw) is 12.1±1.8 kJ mol. These determinations take into account the Fe3+ concentrations that occur in both phases in the presence of metallic Fe. The free energy change in J mol−1 for the Fe exchange reaction can be described, over the range of experimental conditions, by 912 + 4.15 (T−298)+18.9P with T in K, P in kbar. The estimated volume change for this reaction is smaller than that predicted using current compilations of equation
of state data and is much closer to the volume change at ambient conditions. These results are therefore a useful test of
high pressure and temperature equation of state data. Using thermodynamic data consistent with this study the reaction of
ringwoodite to form magnesiowüstite and stishovite is calculated from the data collected using Fe capsules. Comparison of
these results with previous studies shows that the presence of Fe3+ in phases produced in multianvil experiments using Re capsules can have a marked effect on apparent phase relations and determined
thermodynamic properties.
Received: 13 September 2000 / Accepted: 25 March 2001 相似文献
17.
The deviation from stoichiometry, δ, in spinel solid solutions of the type (Ti
x
Fe
1−x
)3−δ O4 with x=0.1, 0.2 and 0.25 was studied thermogravimetrically as a function of oxygen activity, a
O2, at 1100, 1200 and 1300 ∘C. The experimental results, S-shaped curves for δ vs. log aO2, are presented and discussed with regard to the type of point defects prevailing under different conditions in the deviation
from stoichiometry. It is concluded that cation vacancies are the predominant point defects at high oxygen activities, while
cation interstitials prevail at low oxygen activities. The temperature and composition dependencies of point defect concentrations
are also discussed.
Received: 1 October 1996 / Accepted: 15 September 2002
Acknowledgements The authors thank the US Department of Energy for support of this work under Grant no. DE-FGO2–88ER45357. This work made
use of the Cornell Center of Materials Shared Experimental Facilities, supported through the National Science Foundation Materials
Research Science and Engineering Centers program (DMR-0079992). 相似文献
18.
An olivine grain from a peridotite nodule 9206 (Udachnaya kimberlite, Siberia) was investigated by TEM methods including
AEM, HRTEM, SAED and EELS techniques. A previous study of the 9206 olivine sample revealed OH absorption bands in the IR spectrum
and abundant nanometer-sized OH-bearing inclusions, of hexagonal-like or lamellar shape. Inclusions, which are several hundred
nm in size, consist of 10 ? phase, talc and serpentine (chrysotile and lizardite). The lamellar (LI) and hexagon-like small
inclusions of several ten nm in size (SI) are the topic of the present paper. AEM investigations of the inclusions reveal
Mg, Fe and Si as cations only. The Mg/Si and Fe/Si atomic ratios are lower in the inclusions than in the host olivine. The
Si concentration in the olivine host and both lamellar inclusions and small inclusions is the same. A pre-peak at 528eV was
observed in EEL spectra of LI and SI, which is attributed to OH− or Fe3+. From these data it is concluded that there is a OH−- or Fe3+-bearing cation-deficient olivine-like phase present.
HRTEM lattice fringe images of LI and SI exhibit modulated band-like contrasts, which are superimposed onto the olivine lattice.
Diffraction patterns (Fourier-transforms) of the HREM images as well as SAED patterns show that the band-like contrasts in
HRTEM images of the inclusions are caused by periodic modulations of the olivine lattice. Three kinds of superperiodicity
in the olivine structure such as 2a, 3a and 3c, were observed in SAED patterns. The corresponding olivine supercells labelled
here as Hy-2a, Hy-3a and Hy-3c were derived. The M1-vacancies located in the (100) and (001) octahedral layers of the olivine
lattice are suggested to form ordered arrays of planar defects (PD), which cause the band-like contrasts in HRTEM patterns
as well as the superperiodicity in the SAED patterns.
The vacancy concentrations as well as the chemical composition of Hy-2a, Hy-3a and Hy-3c olivine supercells were calculated
using crystal chemical approaches, assuming either {(OH)<
O−V"
Me−(OH)<
O}↔, or {F
e
<
Fe
−H
Me
′}↔ or {2F
e
<
Fe
−V
Me
"}↔ point defect associates. The calculated theoretical compositions Mg1.615Fe+2
0.135v0.25SiO4H0.5 (Hy-2a) and Mg1.54Fe2+
0.12v0.33SiO4H0.66 (Hy-3a and Hy-3c) are in a good agreement with the AEM data on inclusions. Hy-2a, Hy-3a and Hy-3c are considered to be a
hydrous olivine with the extended chemical formula (Mg1-yFe2+
y)2−xvxSiO4H2x. The crystal structure of hydrous olivine is proposed to be a modular olivine structure with Mg-vacant modules. The crystal
chemical formula of hydrous olivines in terms of a modular structure can be written as [MgSiO4H2] · 3[Mg1.82Fe0.18SiO4] for Hy-2a, [MgSiO4H2] · 2[Mg1.82Fe0.18SiO4] for Hy-3a and Hy-3c.
Hydrous olivine is suggested to be exsolved from the olivine 9206, which has been initially saturated by OH-bearing point
defects. The olivine 9206 hydration as well as the following exsolution of hydrous olivine inclusions is suggested to occur
at high pressure-high temperature conditions of the upper mantle.
Received: 15 January 2001 / Accepted: 2 July 2001 相似文献
19.
The cation distribution of Co, Ni, and Zn between the M1 and M2 sites of a synthetic olivine was determined with a single-crystal
diffraction method. The crystal data are (Co0.377Ni0.396Zn0.227)2SiO4, M
r
= 212.692, orthorhombic, Pbnm, a = 475.64(3), b = 1022.83(8), and c = 596.96(6) pm, V = 0.2904(1) nm3, Z = 4, D
x
= 4.864 g cm−3, and F(0 0 0) = 408.62. Lattice, positional, and thermal parameters were determined with MoKα radiation; R = 0.025 for 1487 symmetry-independent reflections with F > 4σ(F). The site occupancies of Co, Ni, and Zn were determined with synchrotron radiation employing the anomalous dispersion effect
of Co and Ni. The synchrotron radiation data include two sets of intensity data collected at 161.57 and 149.81 pm, which are
about 1 pm longer than Co and Ni absorption edges, respectively. The R value was 0.022 for Co K edge data with 174 independent reflections, and 0.034 for Ni K edge data with 169 reflections. The occupancies are 0.334Co + 0.539Ni + 0.127Zn in the M1 sites, and 0.420Co + 0.253Ni + 0.327Zn
in the M2 sites. The compilation of the cation distributions in olivines shows that the distributions depend on ionic radii
and electronegativities of constituent cations, and that the partition coefficient can be estimated from the equation: ln [(A/B)M1/(A/B)M2] = −0.272 (IR
A
-IR
B
) + 3.65 (EN
A
−EN
B
), where IR (pm) and EN are ionic radius and electronegativity, respectively.
Received: 8 April 1999 / Revised, accepted: 7 September 1999 相似文献
20.
Virender K. Sharma Ria A. Yngard Zoltan Homonnay Abhishek Dey Chun He 《Aquatic Geochemistry》2010,16(3):483-490
The kinetics of the formation of the purple-colored species between FeIII-EDTA and peroxynitrite were studied as a function of pH (10.4–12.3) at 22°C in aqueous solutions using a stopped-flow technique.
A purple-colored species was immediately formed upon mixing, which had an absorbance maximum at 520 nm. The increase in absorbance
with time could be fit empirically by a power function with two parameters a and b. The power equation determined was absorbance = a*t
b
, where a increased linearly with pH and the concentration of peroxynitrite, while b almost remained constant with a value of ~0.25. The molar extinction coefficient ε520 nm for the colored species was determined as 13 M−1cm−1, which is much lower than ε520 nm = 520 M−1 cm−1 for the [FeIII(EDTA)O2]3−, a purple species observed in the FeIII–EDTA–H2O2 system. The results of kinetics and spectral measurements of the present study are briefly discussed and compared with those
of the reaction between Fe(III)-EDTA and hydrogen peroxide. 相似文献