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1.
57Fe Mössbauer spectra are presented for synthetic cation-deficient Fe2TiO4 and FeCr2O4 spinel particles (<1μm) at various temperatures. The spectra of ferrimagnetic cation-deficient Fe2TiO4 show characteristic features due to relaxation because of superparamagnetism and spin relaxation in the temperature range 5–294 K. At 5 K and 78 K, a superposition of at least two sextets is observed which appear to arise from Fe3+ onA-sites (Fe A 3+ andB-sites (Fe B 3+ ) of the spinal lattice with magnetic hyperfine fields at 5 K ofB hf ((Fe B 3+ )≈47.5 T andB hf (Fe B 3+ )≈51.0 T, respectively. Cation-deficient FeCr2O4 particles reveal at 78 K a fieldB hf (Fe3+)≈46.9 T and exhibit relaxation spectra as a consequence of superparamagnetism in the temperature range 80 K - ～300 K. At 294 K, quadrupole splitting Δ(Fe A 3+ )=0.92 mm/s and isomer shift δ(Fe A 3+ )=0.29 mm/s (relative to metallic Fe) are measured. For both compounds the magnetic hyperfine fieldsB hf are discussed in terms of supertransferred hyperfine fields involving vacancies and in the case of cation-deficient Fe2TiO4 also diamagnetic Ti4+ neighbours of the Fe ions.  相似文献   

2.
The electron paramagnetic resonance (EPR) spectra of Fe3+ in a well cristallized kaolinite from Decazeville in France are well resolved. It is shown that in this sample there are mainly two slightly different spectra, well separated at low temperature and characterized at -150° C by the constants B 2 0 = 0.112 cm?1, B 2 2 = 0.0688 cm?1 for one and B 2 0 = 0.116 cm?1, B 2 2 = 0.0766 cm?1 for the second. These two spectra arise from Fe3+ substituted for Al3+ at the two octahedral positions in equal amounts. The temperature dependence of EPR spectra was studied and was explained by a modification of the octahedral sites.  相似文献   

3.
The mixed valence iron silicate ilvaite, CaFe 2 2+ Fe3+Si2O8(OH), displays electron delocalization associated with Fe2+→Fe3+ charge transfer as observed by Mössbauer spectroscopy. Previous studies report the observation of an ‘electron hopping phenomenon’ with resolution of discrete valence states below 320 K. Mössbauer spectra of a suite of naturally occurring ilvaites were recorded over a temperature range, 80 K to 575 K. Five quadrupole doublets were resolved by computer fitting and assigned to Fe2+(A), Fe2+(B), Fe3+(A), and Fe2+(A)→Fe3+(A)‖c and ⊥c. Contrary to prior work, doublets associated with electron delocalization are resolved at 80 K and preclude the use of a Verwey-type order-disorder model. We propose a thermal activation model and discuss its criteria from molecular orbital and mineralogical viewpoints.  相似文献   

4.
Laihuite reported in the present paper is a new iron silicate mineral found in China with the following characteristics:
  1. This mineral occurs in a metamorphic iron deposit, associated with fayalite, hypersthene, quartz, magnetitc, etc.
  2. The mineral is opaque, black in colour, thickly tabular in shape with luster metallic to sub-metallic, two perfect cleavages and specific gravity of 3.92.
  3. Its main chemical components are Fe and Si with Fe3+>Fe2+. The analysis gave the formula of Fe Fe 1.00 3+ ·Fe 0.58 2+ ·Mg 0.03 2+ ·Si0.96O4.
  4. Its DTA curve shows an exothermic peak at 713°C.
  5. The mineral has its own infrared spectrum distinctive from that of other minerals.
  6. This mineral is of orthorhombic system; space group:C 2h /5 ?P21/c; unit cell:α=5.813ű0.005,b=4.812ű0.005,c=10.211ű0.005,β=90.87°.
  7. The Mössbauer spectrum of this mineral is given, too.
  相似文献   

5.
Manganoan lipscombite (Fe x /2+ , M y /2+ ) Fe 3?(x +y)/3+ [OH)3?(x+y)(PO4)2] was synthesized from pure chemicals. From the study of the Mn2+/Fe2+ atomic ratio by Mössbauer spectra, solubility, and electrokinetic properties, it was found that the crystal structure of lipscombite is not changed substantially by the manganese substitution. The unit cell parameters were determined from Guinier-Hägg X-ray diffraction patterns, which are identical for both synthetic ferrous-ferric and manganoan lipscombite. The two compounds crystallize in the tetragonal system with a=5.3020±0.0005 Å and c=12.8800±0.0005 Å.  相似文献   

6.
Non-metamict perrierite-(La) discovered in the Dellen pumice quarry, near Mendig, in the Eifel volcanic district, Rheinland-Pfalz, Germany has been approved as a new mineral species (IMA no. 2010-089). The mineral was found in the late assemblage of sanidine, phlogopite, pyrophanite, zirconolite, members of the jacobsite-magnetite series, fluorcalciopyrochlore, and zircon. Perrierite-(La) occurs as isolated prismatic crystals up to 0.5 × 1 mm in size within cavities in sanidinite. The new mineral is black with brown streak; it is brittle, with the Mohs hardness of 6 and distinct cleavage parallel to (001). The calculated density is 4.791 g/cm3. The IR spectrum does not contain absorption bands that correspond to H2O and OH groups. Perrierite-(La) is biaxial (-), α = 1.94(1), β = 2.020(15), γ = 2.040(15), 2V meas = 50(10)°, 2V calc = 51°. The chemical composition (electron microprobe, average of seven point analyses, the Fe2+/Fe3+ ratio determined from the X-ray structural data, wt %) is as follows: 3.26 CaO, 22.92 La2O3, 19.64 Ce2O3, 0.83 Pr2O2, 2.09 Nd2O3, 0.25 MgO, 2.25 MnO, 3.16 FeO, 5.28 Fe2O3, 2.59 Al2O3, 16.13 TiO2, 0.75 Nb2O5, and 20.06 SiO2, total is 99.21. The empirical formula is (La1.70Ce1.45Nd0.15Pr0.06Ca0.70)Σ4.06(Fe 0.53 2+ Mn0.38Mg0.08)Σ0.99(Ti2.44Fe 0.80 3+ Al0.62Nb0.07)Σ3.93Si4.04O22. The simplified formula is (La,Ce,Ca)4(Fe2+,Mn)(Ti,Fe3+,Al)4(Si2O7)2O8. The crystal structure was determined by a single crystal. Perrierite-(La) is monoclinic, space group P21/a, and the unit-cell dimensions are as follows: a =13.668(1), b = 5.6601(6), c = 11.743(1) Å, β = 113.64(1)°; V = 832.2(2) Å3, Z = 2. The strong reflections in the X-ray powder diffraction pattern are [d, Å (I, %) (hkl)]: 5.19 (40) (110), 3.53 (40) ( $\overline 3 $ 11), 2.96 (100) ( $\overline 3 $ 13, 311), 2.80 (50) (020), 2.14 (50) ( $\overline 4 $ 22, $\overline 3 $ 15, 313), 1.947 (50) (024, 223), 1.657 (40) ( $\overline 4 $ 07, $\overline 4 $ 33, 331). The holotype specimen of perrierite-(La) is deposited at the Fersman Mineralogical Museum, Russian Academy of Sciences, Moscow, Russia, with the registration number 4059/1.  相似文献   

7.
The transformation of vivianite and the direct synthesis starting from pure chemicals lead to the formation of lipscombite {Fe x 2+ Fe 3?x 3+ [(OH)3?x/(PO4)2]} with varying Fe2+/Fe3+ molar ratios. The influence of this ratio on the Mössbauer spectra, solubility, electrokinetic potential and infrared spectra has been studied. By means of Mössbauer spectroscopy, the distribution of the Fe2+ and Fe3+ ions between the octahedral sites I and II has been investigated. The unit cell dimensions have been determined from Guinier-Hägg X-ray diffraction patterns. The crystal system is tetragonal for synthetic lipscombite with a=5.3020±0.0005 Å and c=12.8800±0.0005 Å. Lipscombite has been found to show a negative and time-dependent zeta-potential which, moreover, is influenced by the pH of the suspension and the Fe2+/Fe3+ molar ratio. An explanation of the time-dependence of the zeta-potential on variations of solubility is proposed. Infrared absorption spectrum only is characterized by two absorption bands: v OH(3,500 cm?1) and v P?O(1,100-960 cm?1). The density at 25° C is determined in toluene as 3.36±0.01 g·cm?3.  相似文献   

8.
A new mineral, ferrotochilinite, ideally 6FeS · 5Fe(OH)2, was found at the Oktyabr’sky Mine, Oktyabr’skoe Cu-Ni deposit, Noril’sk, Krasnoyarsk krai, Siberia, Russia. It is associated with ferrovalleriite, magnetite and Fe-rich, chlorite-like phyllosilicate in the cavities of pentlandite-mooihoekite-cubanite ore with subordinate magnetite and chalcopyrite. Ferrotochilinite occurs as flattened on [001], prismatic to elongated lamellar crystals up to 0.1 × 0.5 × 3.2 mm, typically split and curved. Aggregates (up to 6.5 mm in size) are fanlike, rosette-like, or chaotic. Ferrotochilinite is dark bronze. The streak is black. The luster is moderately metallic. The Mohs’ hardness is ca. 1; VHN is 13 kg/mm2. Cleavage is {001} perfect, micalike. Individuals are flexible, inelastic. D(calc) = 3.467 g/cm3. In reflected light, ferrotochilinite is gray, with the hue changing from pale beige to bluish; bireflectance is distinct. Anisotropy is distinct, with gray bluish to yellowish beige rotation colors. No internal reflections. Reflectance values [R min-R max, % (λ, nm)] are: 11.6–11.4 (470), 11.2–12.4 (546), 11.1–13.6 (589), 11.0–15.5 (650). The IR spectrum shows the presence of (OH) groups bonded with Fe cations and the absence of H2O molecules. Chemical composition (wt %; electron probe; H content is calculated) is as follows: 0.02 Mg, 61.92 Fe, 0.03 Ni, 0.09 Cu, 19.45 S, 16.3 O, 1.03 H calc; the total is 98.84. The empirical formula calculated on the basis of 6 S atoms is: Mg0.01Fe10.96Ni0.005Cu0.015S6(OH)10.07 = (Fe5.98Cu0.0015Ni0.005)Σ6S6(OH)9.80(Fe 4.89 2+ Mg0.01)Σ4.90(OH)9.80Fe 0.09 3+ (OH)0.27. Ferrotochilinite is monoclinic, space group is C2/m, Cm or C2, the unit-cell dimensions are: a = 5.463(5), b = 15.865(17), c = 10.825(12) Å, β = 93.7(1)°, V = 936(3) Å3, Z = 2. The strongest reflections in the X-ray powder diffraction pattern (d, Å-I[hkl]) are: 10.83-13[001], 5.392-100[002], 3.281-7[023], 2.777-7[150], 2.696-12[004, $20\bar 1$ ], 2.524-12[ $22\bar 1$ , $20\bar 2$ ], 2.152-8[134, 153], 1.837-11[135, $17\bar 3$ ]. Ferrotochilinite is a structural analog of tochilinite, with Fe2+ instead of Mg in the hydroxide part. The type specimen is deposited in Fersman Mineralogical Museum of Russian Academy of Sciences, Moscow.  相似文献   

9.
The ‘average’ interdiffusion coefficient ( \(\bar D\) ) for NaSi—CaAl exchange in plagioclase for the interval from An0 to An26 was estimated from experimentally determined homogenization times for peristerite exsolution lamellae. The average spacing between adjacent (unlike) lamellae is 554±77 Å. Dry heating in air at 1,100°C for 98 days produced no change in the exsolution microstructure; thus \(\bar D\) (dry)<10?17 cm2/s. This limit is consistent with the recently reported ‘average’ \(\bar D\) (dry) values for the Huttenlocher interval (An70–90) at this temperature. At 1.5 GPa with about 0.2 weight percent water added the ‘average’ diffusion coefficient from 1,100°C to 900°C is given by: \(\bar D\) (wet)=18 ?15 +108 (cm2/s) exp (?97±5 (kcal/mol)/RT), where R is the gas constant, and T is °K. This \(\bar D\) (wet) at 1,100°C is more than three orders of magnitude greater than \(\bar D\) (dry) for Na- and Ca-rich plagioclases.  相似文献   

10.
A new Cu-rich variety of lyonsite has been found from fumarolic sublimates of the Tolbachik volcano (Kamchatka, Russia). The empirical formula is Cu4.33Fe 2.37 3+ Ti0.26Al0.26Zn0.07(V5.85As0.07Mo0.07P0.01S0.01)O24. The crystal structure was studied on single crystal using synchrotron radiation, R = 0.0514. The mineral is orthorhombic, Pnma, a = 5.1736(7), b =10.8929(12), c = 18.220(2) Å, V = 1026.8(2) Å3, and Z = 2. The structural formula is (Cu0.6Ti0.3Al0.3Fe 0.2 3+ □0.6)Σ2Cu2(Fe 2.2 3+ Cu1.8)Σ4(V5.8As0.1Mo0.1)Σ6O24. It is proposed to recast the simplified formula of lyonsite as Cu3+x (Fe 4?2x 3+ Cu2x )(VO4)6, where 0 ≤ x ≤ 1.  相似文献   

11.
A new coexisting amphibole pair was recently found in the Jianshan iron deposit, Loufan of Shanxi Province, China. Electron microprobe analysis shows that the coexisting pair is composed of grünerite K0.001 (Na0.027 Ca0.073 Mn0.031 Fe 1.801 2+ )1.932 (Fe 2.948 2+ Mg1.964 Ti0.002 Al0.087)5Si8.069 O22.10(OH)2 and ferropargasite (K0.135 Na0.461)0.596 (Na0.088 Ca1.853 Mn0.005 Fe 0.072 2+ )2(Mn0.005Fe 2.789 2+ Mg0.875Ti0.021Fe 0.499 3+ Al0.812)5(Si6.103Al1.897)8O22.00(OH)2. The two kinds of amphiboles occur in amphibole schist not only as separate phenocrysts, but also are combined to form “single-crystal” phenocrysts in the form of topotactic intergrowths with the common c- and b-axes. The boundary between topotactic grünerite and ferropargasite is optically and chemically sharp. In comparison with the coexisting ferromagnesian amphibole and calcic amphibole pair discovered by predecessors, the newly discovered pair has lower Mg/Fe ratios and wider miscibility gaps.  相似文献   

12.
Exchange-mineral equilibria with Al and Fe3+ aqueous chloride solutions (aq.), Andr + AlCl aq 3 = FeCl aq 3 + Gros, (1) Psc + AlCl aq 3 = FeCl aq 3 + Czo, (2) were studied under the following experimental conditions: 500°;C and 580°;C and 1 and 2 kbar, respectively, with an overall concentration of metals in the aqueous solutions of about 0.5 M and pH 3. The mixing functions of the components in garnet and epidote were calculated from the experimental data. Thermodynamic treatment of experimental evidence for reaction (1) led to the conclusion that, within the accuracy of experiment, garnet in the andradite-grossularite series was an ideal solid solution. However, epidote solid solution markedly departed from the ideal, as was shown by concentration and pressure-temperature (PT) dependencies of Gibbs's molar excess energies and by mixing-volume concentration dependence.  相似文献   

13.
Kinetic rates of Fe2+-Mg disordering in three orthopyroxenes (mean value of XFe = Fe2+/(Fe2++Mg) = 0.175,0.482,0.770 respectively) have been determined employing heating experiments and single crystal X-ray structural refinements. Disordering rate constants \((\vec K)\) (550800° C) for two pyroxenes are given by: ln \((\vec K)\) = 27.107(±5.177)?32062(±783)T?1(XFe = 0.175) ln \((\vec K)\) = 16.142(±0.057)?18227(±423)T?1(XFe = 0.770) The distribution coefficients KD (representing a steady state of disordering FeM2 + MgM1 ? FeM1 + MgM2) are given by: ln KD = 5.016(±0.223)-7033(±1473) T?1(XFe = 0.175) ln KD = 1.988(±0.122)-3809(±913)T?1(XFe = 0.770) These distribution coefficients provide the constraint of the disordering reaction on the value of the equilibrium constant for Fe2+-Mg order-disorder. Until the low temperature dependence of KD is well constrained, the calculation of cooling rates of pyroxenes and host rocks cannot be done reliably.  相似文献   

14.
Fluids at crustal pressures and temperatures   总被引：1，自引：0，他引：1  
  相似文献   

15.
This paper presents the point-defect thermodynamics for fayalite and olivine solid solutions (Fe x Mg1?x )2SiO4. By means of thermogravimetry, the metal-to-oxygen ratio of these silicates has been determined as a function of oxygen potential, compositionx and temperature. Experiments were performed in the range of 1,000° C≦T≦1,280° C and 0.2≦x≦1.0. It is found that V Me ″ , Fe Me · and the associate {Fe′ Si ′ Fe Me · } are the majority defects. With this knowledge it is possible to calculate the nonstoichiometry at given temperature as a function of \(p_{O_2 } \) and \(a_{SiO_2 } \) . The cation vacancy concentration shows a \(p_{O_2 }^{1/5} \) -dependence (forx≧0.2) and increases at givenT and \(p_{O_2 } \) almost exponentially with compositionx. In the composition range studied here, the silicates show an oxygen excess, and FeO is more soluble in the olivine than SiO2.  相似文献   

16.
The results of thermochemical studies are reported for nontronite samples from the Pinares-de-Majari (Eastern Cuba) (Sample I) and Kempirsai serpentine massif (South Urals, Kazakhstan) (Sample II). The enthalpies of formation of dehydrated hydroxyl-bearing nontronites from elements were determined by melt dissolution calorimetry using high-temperature heat-flux Tiana-Calvet microcalorimeter: Δ f H el o (298.15 K): ?4958 ± 13 kJ/mol for Mg0.4(Fe 1.5 3+ Mg0.4Ni0.1)[Si3.7Al0.3O10](OH)2 (I) and ?5003.6 ± 8.0 kJ/mol for Mg0.3Na0.1Ca0.1(Fe 1.4 3+ Mg0.5Ni0.1)[Si3.7Al0.3O10](OH)2 (II). It was determined experimentally that the enthalpy of dehydration (removal of molecular adsorption and interlayer water) of the studied nontronites is 6 ± 2 kJ per 1 mole H2O. The enthalpy of formation of nontronite of theoretical composition Mg0.15Fe 2 3+ [Si3.7Al0.3]O10(OH)2 was estimated at ?4750 kJ/mol. The Gibbs free energies of formation of the nontronites were calculated.  相似文献   

17.
Ephesite, Na(LiAl2) [Al2Si2O10] (OH)2, has been synthesized for the first time by hydrothermal treatment of a gel of requisite composition at 300≦T(° C)≦700 and \(P_{H_2 O}\) upto 35 kbar. At \(P_{H_2 O}\) between 7 and 35 kbar and above 500° C, only the 2M1 polytype is obtained. At lower temperatures and pressures, the 1M polytype crystallizes first, which then inverts to the 2M1 polytype with increasing run duration. The X-ray diffraction patterns of the 1M and 2M1 poly types can be indexed unambiguously on the basis of the space groups C2 and Cc, respectively. At its upper thermal stability limit, 2M1 ephesite decomposes according to the reaction (1) $$\begin{gathered} {\text{Na(LiAl}}_{\text{2}} {\text{) [Al}}_{\text{2}} {\text{Si}}_{\text{2}} {\text{O}}_{{\text{10}}} {\text{] (OH)}}_{\text{2}} \hfill \\ {\text{ephesite}} \hfill \\ {\text{ = Na[AlSiO}}_{\text{4}} {\text{] + LiAl[SiO}}_{\text{4}} {\text{] + }}\alpha {\text{ - Al}}_{\text{2}} {\text{O}}_{\text{3}} {\text{ + H}}_{\text{2}} {\text{O}} \hfill \\ {\text{nepheline }}\alpha {\text{ - eucryptite corundum}} \hfill \\ \end{gathered}$$ Five reversal brackets for (1) have been established experimentally in the temperature range 590–750° C, at \(P_{H_2 O}\) between 400 and 2500 bars. The equilibrium constant, K, for this reaction may be expressed as (2) $$log K{\text{ = }}log f_{{\text{H}}_{\text{2}} O}^* = 7.5217 - 4388/T + 0.0234 (P - 1)T$$ where \(f_{H_2 O}^* = f_{H_2 O} (P,T)/f_{H_2 O}^0\) (1,T), with T given in degrees K, and P in bars. Combining these experimental data with known thermodynamic properties of the decomposition products in (1), the following standard state (1 bar, 298.15 K) thermodynamic data for ephesite were calculated: H f,298.15 0 =-6237372 J/mol, S 298.15 0 =300.455 J/K·mol, G 298.15 0 =-5851994 J/mol, and V 298.15 0 =13.1468 J/bar·mol.  相似文献   

18.
Violet, non-pleochroic and greenish-blue, pleochroic chromium-substituted sapphirines were found in corundum-bearing spinel-websterite xenolites from the Yakutian kimberlite pipes Noyabrskaya (N) and Sludyanka (Sl), respectively. The crystallochemical formulae of sapphirine crystals from such xenolites were determined by EMP to be (Mg3.40Fe0.23Al3.25Cr0.16)[6] Al 1.00 [6] [O2/Al4.53Si1.47O18] (N) and (Mg2.53Fe0.55 Mn0.04Ti 0.03 4+ Al3.55Cr 0.08 3+ )[6]Al 1.00 [16] [O2/Al4.28Si1.73O18] (Sl). Single crystal spectra in the range 35000–6000 cm1- showed a slightly polarization dependent absorption edge near 3200 cm1- (N) or 30000 cm1- (Sl) and unpolarized bands at 25300 and 17300 cm1-, typical of spin-allowed transitions, derived from 4A2g→4T1g and 4A2g→4T2g, of Cr3+ in octahedral sites, with point symmetry C1, of the structure. Another weak band at 23000 cm?1 in the sapphirine-N spectra is attributed to low symmetry splitting of the excited 4T1 (F)-State of Cr3+. These assignments lead to crystal field parameters Dq=1730cm?1 and B= 685cm?1 of Cr3+ in sapphirine. Crystallochemical and spectroscopic arguments suggest that Cr3+ subsitutes for Al in the M(1) or M(8) sites of the sapphirine structure. In addition to Cr3+-transitions, spectra of Sl exhibit weak dd-bands of Fe2+ at 10000 and 7700 cm1-, which are unpolarized in consistency with the C1 site symmetry of the octahedra in the structure. Spectra of Sl show also prominent, broad bands (Δv1/2～-5000 cm1-) at 15000 and 11000 cm1-, which occur in E//Y(//b) and E//Z(//c=12°) only and exhibit an intensity ratio αY∶αz close to 1∶3. This result, the large half width, as well as band energy — MM distance considerations suggest that these bands originate from Fe2+[6]-Fe3+[6] charge-transfer transitions in wall octahedra M(1)M(2), M(6)M(7) etc., forming MM vectors of 30° with the c-axis. The lack of Fe2+-Fe3+ charge-transfer bands in sapphirine N might indicate a lower oxygen fugacity during the formation of the websterite from the Noyabrskaya pipe compared to that from the Sludyanka pipe.  相似文献   

19.
Given the direction cosines a i ′ = (a 1 i , a 2 i , a 3 i )corresponding to a set of pspherically projected fabric poles, an initial estimate x′ = (x1, x2, x3, x4)for the angular radius x4,and direction cosines of the center of the least-squares small circle which minimizes the sum of the squares of the angular residuals $$r = \sum\limits_p {\left[ {x_4 - \cos ^{ - 1} \left( {a_1^i x_1 + a_2^i x_2 + a_3^i x_3 } \right)} \right]} ^2 $$ can be iteratively improved by taking xj+1 = xj + Δxwhere xj is the value of xat the jth iteration and $$\Delta x = - H_j^{ - 1} \left[ {q_j + x_j \left( {x'_j H_j^{ - 1} x_j } \right)\left( {q_j - x'_j H_j^{ - 1} q_j } \right)} \right],$$ where As an initial approximation for xwe have found it convenient to ignore the fact that the data are constrained to lie on the surface of the reference sphere and to use the parameters of a least-squares plane through the given poles. Generalization of this approach to fitting variously constrained great and small circles is easily made. The relative merits of differently constrained fits to the same data can be tested approximately if it is assumed that the errors in the location of the poles are isotropic and normally distributed. It is thus possible to statistically assess the relative significance of conflicting structural models which predict different geometrical patterns of fabric elements.  相似文献   

20.
The \(\mu _{O_2 } \) defined by the reaction 6 MnO+O2 =2 Mn3O4 has been determined from 917 to 1,433 K using electrochemical cells (with calcia-stabilized zirconta, CSZ) of the type: Steady emfs were achieved rapidly at all temperatures on both increasing and decreasing temperature, indicating that the MnO-Mn3O4 oxygen buffer equilibrates relatively easily. It therefore makes a useful alternative choice in experimental petrology to Fe2O3-Fe3O4 for buffering oxygen potentials at oxidized values. The results are (in J/mol, temperature in K, reference pressure 1 bar); \(\mu _{O_2 } \) (±200)=-563,241+1,761.758T-220.490T inT+0.101819T 2 with an uncertainty of ±200 J/mol. Third law analysis of these data, including a correction for the deviations in stoichiometry of MnO, impliesS 298.15 for Mn3O4 of 166.6 J/K · mol, which is 2.5 J/K · mol higher than the calorimetric determination of Robie and Hemingway (1985). The low value of the calorimetric entropy may be due to incomplete ordering of the magnetic spins. The third law value of Δ r H 298.15 0 is-450.09 kJ/mol, which is significantly different from the calorimetric value of-457.5±3.4 kJ/mol, calculated from Δ f H 298.15 0 of MnO and Mn3O4, implying a small error in one or both of these latter.  相似文献   

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