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Alexander N. Krot - One of the best experts on this subject based on the ideXlab platform.
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oxygen isotope heterogeneity in the northwest africa 3358 h3 1 refractory inclusions fluid assisted isotopic exchange on the h chondrite parent body
Geochimica et Cosmochimica Acta, 2020Co-Authors: S Ebert, Alexander N. Krot, Kazuhide Nagashima, A BischoffAbstract:Abstract The nature of oxygen-isotope heterogeneity in refractory inclusions [Ca,Al-rich inclusions (CAIs) and amoeboid olivine aggregates (AOAs)] from weakly metamorphosed chondrites is one of the outstanding problems in cosmochemistry. To obtain insights into possible processes resulting in O-isotope heterogeneity of refractory inclusions, we investigated the mineralogy, petrology, and oxygen isotopic compositions of six CAIs and two AOAs and aqueously formed Fayalite grains within the matrix of the H3.1 chondrite Northwest Africa (NWA) 3358. Most of the refractory inclusions studied appear to be unmolten solar nebula condensates; some may have experienced partial melting and/or high-temperature annealing. The NWA 3358 refractory inclusions nearly completely avoided metasomatic alteration on the H-chondrite parent body: nepheline grains replacing anorthite and/or melilite are either very minor or absent. Five out of eight refractory inclusions studied have heterogeneous O-isotope composition: Δ17O ranges from ∼− 25‰ to ∼3.5 ± 2‰ (2σ). This O-isotope heterogeneity appears to be mineralogically controlled with melilite and anorthite being systematically 16O-depleted compared to hibonite, spinel, Al,Ti-diopside, and forsterite all having similar solar-like Δ17O of ∼−24 ± 2‰. In contrast to NWA 3358 refractory inclusions, the previously studied AOAs and a fine-grained CAI from the LL3.00 chondrite Semarkona have uniform Δ17O of ∼−25‰ ( Itoh et al., 2007 , McKeegan et al., 1998 ). Because the mineralogically-controlled O-isotope heterogeneity in refractory inclusions from ordinary chondrites appears to correlate with petrologic type of a host meteorite experienced by aqueous alteration, we suggest O-isotope exchange in NWA 3358 CAIs and AOAs resulted from aqueous fluid-rock interaction on the H-chondrite parent asteroids. This is supported by the presence of 16O-depleted anorthite (Δ17O ∼ 3.5 ± 2‰) and aqueously formed Fayalite similar depleted in 16O (Δ17O ∼ 4 ± 2‰). The Δ17O of NWA 3358 Fayalite is comparable to that of magnetite and Fayalite in Semarkona and other weakly metamorphosed L3 and LL3 chondrites ( Choi et al., 1998 , Doyle et al., 2015 ) suggesting similar Δ17O of aqueous fluids on the H, L, and LL chondrite parent asteroids.
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mn cr relative sensitivity factor in ferromagnesian olivines defined for sims measurements with a cameca ims 1280 ion microprobe implications for dating secondary Fayalite
Geochimica et Cosmochimica Acta, 2016Co-Authors: P M Doyle, G R Huss, K Jogo, Kazuhide Nagashima, Alexander N. KrotAbstract:Abstract The short-lived radionuclide 53Mn, which decays to 53Cr with a half-life of ∼3.7 Myr, is useful for sequencing objects that formed within the first 20 Myr of Solar System evolution. 53Mn–53Cr relative chronology enables aqueously formed secondary minerals such as Fayalite and various carbonates in ordinary and carbonaceous chondrites to be dated, thereby providing chronological constraints on aqueous alteration processes. In situ measurements of Mn–Cr isotope systematics in Fayalite by secondary ion mass spectrometry (SIMS) require consideration of the relative sensitivities of the 55Mn+ and 52Cr+ ions, for which a relative sensitivity factor [RSF = (55Mn+/52Cr+)SIMS/(55Mn/52Cr)true] is defined using appropriate standards. In the past, San Carlos olivine (Fa∼10) was commonly used for this purpose, but a growing body of evidence suggests that it is an unsuitable standard for meteoritic Fayalite (Fa>90). Natural Fayalite also cannot be used as a standard because it contains only trace amounts of chromium, which makes determining a true 55Mn/52Cr ratio and its degree of heterogeneity very difficult. To investigate the dependence of the Mn–Cr RSF on ferromagnesian olivine compositions, we synthesized a suite of compositionally homogeneous Mn,Cr-bearing liquidus-phase ferromagnesian olivines (Fa31–99). Manganese–chromium isotopic measurements of San Carlos olivine and synthesized ferromagnesian olivines using the University of Hawai‘i Cameca ims-1280 SIMS show that the RSF for Fa10 is ∼0.9; it increases rapidly between Fa10 and Fa31 and reaches a plateau value of ∼1.5 ± 0.1 for Fa>34. The RSF is time-dependent: it increases during the measurements of olivines with Fayalite content 50. The RSF measured on ferroan olivine (Fa>90) is influenced by pit shape, whereas the RSF measured on magnesian olivine (Fa10) is less sensitive to changes in pit shape. For these reasons, 53Mn–53Cr systematics of chondritic Fayalite (Fa>90) should be determined using standards of similar composition that are measured under the same analytical conditions as the “unknown”. The 53Mn–53Cr ages of secondary Fayalites (Fa90–100) in the Elephant Moraine (EET) 90161 (L3.05), Vicencia (LL3.2), Asuka 881317 (CV3) and MacAlpine Hills (MAC) 88107 (C3) chondrites ( 2.4 - 1.3 + 1.8 , 4.0 - 1.1 + 1.4 , 4.2 - 0.7 + 0.8 and 5.1 - 0.4 + 0.5 Myrs after CV CAIs, respectively) are ∼3 Myr older when using an RSF measured on a matrix-matched (Fa99) standard, rather than on a San Carlos olivine. The inferred 53Mn–53Cr ages of Fayalite formation are consistent with the ages reported for calcites in CM chondrites measured with similarly matrix-matched standards, suggesting an early onset of aqueous alteration on the ordinary and carbonaceous chondrite parent bodies heated by decay of 26Al.
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early aqueous activity on the ordinary and carbonaceous chondrite parent bodies recorded by Fayalite
Nature Communications, 2015Co-Authors: Alexander N. Krot, Kaori Jogo, Kazuhide Nagashima, Patricia M Doyle, Shigeru Wakita, Fred J Ciesla, I D HutcheonAbstract:The parent bodies of many chondritic meteorites experienced aqueous alteration, the chronology of which helps constrain their histories. Here, the authors synthesize a Fayalite standard and report reliable ages of secondary Fayalite, from which model accretion ages are determined and the place of accretion is inferred.
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the vicencia meteorite fall a new unshocked s1 weakly metamorphosed 3 2 ll chondrite
Meteoritics & Planetary Science, 2015Co-Authors: K Keil, Alexander N. Krot, Patricia M Doyle, John T Wasson, Maria Elizabeth Zucolotto, Myriam Telus, Tatiana V Krot, R C Greenwood, I A Franchi, K C WeltenAbstract:The Vicencia meteorite, a stone of 1.547 kg, fell on September 21, 2013, at the village Borracha, near the city of Vicencia, Pernambuco, Brazil. It was recovered immediately after the fall, and our consortium study showed it to be an unshocked (S1) LL3.2 ordinary chondrite. The LL group classification is based on the bulk density ($3.13\; g\; cm^{-3}$); the chondrule mean apparent diameter (0.9 mm); the bulk oxygen isotopic composition ($\delta^{17}O=3.768\pm0.042{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$, $\delta^{18}O=5.359\pm0.042{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$, $\Delta^{17}O = 0.981\pm 0.020{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$); the content of metallic Fe,Ni (1.8 vol%); the Co content of kamacite (1.73 wt%); the bulk contents of the siderophile elements Ir and Co versus Au; and the ratios of metallic $Fe^{0}$/total iron (0.105) versus total Fe/Mg (1.164), and of Ni/Mg (0.057) versus total Fe/Mg. The petrologic type 3.2 classification is indicated by the beautifully developed chondritic texture, the standard deviation (~0.09) versus mean $Cr_{2}O_{3}$ content (~0.14 wt%) of ferroan olivine, the TL sensitivity and the peak temperature and peak width at half maximum, the cathodoluminescence properties of chondrules, the content of trapped $^{132}Xe_{tr}$(0.317 × $10^{-8}cm^{3}STP\; g^{-1}$), and the Raman spectra for organic material in the matrix. The cosmic ray exposure age is ~72 Ma, which is at the upper end of the age distribution of LL group chondrites. The meteorite is unusual in that it contains relatively large, up to nearly 100 μm in size, secondary Fayalite grains, defined as olivine with $Fa_{{\textgreater}75}$, large enough to allow in situ measurement of oxygen and Mn-Cr isotope systematics with SIMS. Its oxygen isotopes plot along a mass-dependent fractionation line with a slope of ~0.5 and ${\Delta}17O$ of $4.0 \pm 0.3{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$, and are similar to those of secondary Fayalite and magnetite in the unequilibrated chondrites EET 90161, MET 96503, and Ngawi. These data suggest that secondary Fayalite in Vicencia was in equilibrium with a fluid with a $\Delta^{17}O$ of ~$4{}^\text{o}\mkern-5mu/\mkern-3mu_\text{oo}$, consistent with the composition of the fluid in equilibrium with secondary magnetite and Fayalite in other unequilibrated ordinary chondrites. Secondary Fayalite and the chondrule olivine phenocrysts in Vicencia are not in isotopic equilibrium, consistent with low-temperature formation of Fayalite during aqueous alteration on the LL parent body. That alteration, as dated by the $^{53}Mn-^{53}Cr$ chronology age of secondary Fayalite, took place $4.0^{+1.4}_{-1.1}$Ma after formation of CV CAIs when anchored to the quenched angrite D'Orbigny.
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oxygen isotopes in magnetite and Fayalite in cv chondrites kaba and mokoia
Meteoritics & Planetary Science, 2000Co-Authors: Alexander N. Krot, Byeongak Choi, John T WassonAbstract:— We report in situ measurements of O-isotopic compositions of magnetite and primary and secondary olivine in the highly unequilibrated oxidized CV chondrites Kaba and Mokoia. In both meteorites, the magnetite and the secondary olivine (Fayalite, Fa90–100) have O-isotopic compositions near the terrestrial fractionation (TF) line; the mean Δ17O (= δ17O-0.52 × δ18O) value is about −1%‰. In contrast, the compositions of nearby primary (chondrule), low-FeO olivines (Fa1–2) are well below the TF line; Δ17O values range from −3 to −9%‰. Krot et al. (1998) summarized evidence indicating that the secondary phases in these chondrites formed by aqueous alteration in an asteroidal setting. The compositions of magnetite and Fayalite in Kaba and Mokoia imply that the O-isotopic composition of the oxidant was near or somewhat above the TF line. In Mokoia the Fayalite and magnetite differ in δ18O by ∼20%‰, whereas these same materials in Kaba have virtually identical compositions. The difference between Mokoia magnetite and Fayalite may indicate formation in isotopic equilibrium in a water-rich environment at low temperatures, ∼300 K. In contrast, the similar compositions of these phases in Kaba may indicate formation of the Fayalite by replacement of preexisting magnetite in dry environment, with the O coming entirely from the precursor magnetite and silica. The Δ17O of the oxidant incorporated into the CV parent body (as phyllosilicates or H2O) appears to have been much (7–8%‰) lower than that in that incorporated into the LL parent body (Choi et al, 1998), which suggests that the O-isotopic composition of the nebular gas was spatially or temporally variable.
Edgar Dachs - One of the best experts on this subject based on the ideXlab platform.
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the heat capacity of Fayalite at high temperatures
American Mineralogist, 2012Co-Authors: Artur Benisek, Herbert Kroll, Edgar DachsAbstract:The high-temperature heat capacity of Fayalite was reinvestigated using drop and differential scanning calorimetry. The resulting data together with drop calorimetry data taken from the literature were analyzed yielding C P J/(mol·K) = −584.388 + 129 440· T −1 − 3.84956·107· T −2 + 4.10143·109· T −3 + 98.4368·ln( T ). This new C P polynomial is recommended for calculating phase equilibria involving Fayalite at mantle conditions. Using thermal expansion coefficient and isothermal bulk modulus data from the literature, the isochoric heat capacity was calculated resulting in C V J/(mol·K) = − 217.137 + 63 023.1· T −1 − 2.15863·107· T −2 + 2.23513·109· T −3 + 51.7620·ln( T ).
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a low temperature calorimetric study of synthetic forsterite Fayalite mg2sio4 fe2sio4 solid solutions an analysis of vibrational magnetic and electronic contributions to the molar heat capacity and entropy of mixing
The Journal of Chemical Thermodynamics, 2007Co-Authors: Edgar Dachs, Charles A Geiger, Volker Von Seckendorff, Michael GrodzickiAbstract:Abstract The molar heat capacities (Cp,m) of a series of synthetic forsterite (Fo)–Fayalite (Fa), (Mg2SiO4 + Fe2SiO4), olivines have been measured between 5 K and 300 K on milligram-sized samples with the Physical Properties Measurement System (Quantum Design®). Sharp, λ-type heat capacity anomalies are observed in the Fe-rich compositions Fayalite, Fo10Fa90, Fo20Fa80, Fo30Fa70, and Fo40Fa60. The corresponding Neel temperatures TN decrease linearly from 64.5 K in Fayalite to 32.8 K in Fo40Fa60 following the relationship TN = 79.02 · xFa − 14.07. Fo50Fa50 and Mg-richer olivines show weak broad features in the heat capacity data around 15 K to 20 K that decrease in magnitude with increasing forsterite content. In order to derive and separate molar electronic, magnetic and vibrational heat capacity contributions, Cel,m, Cmag,m, and Cvib,m from the experimental heat capacities (Ctot,m), we used a single-parametric phonon dispersion model to calculate Cvib,m for the solid-solution members and Fayalite. The Cel,m + Cmag,m(= Ctot,m − Cvib,m) contributions were fit to expressions describing a Schottky-type electronic anomaly and a paramagnetic–antiferromagnetic transition. For Fo50Fa50 and Mg-richer olivines, our analysis of Ctot,m shows that also these compositions have a Cmag,m contribution with a maximum around 25 K. Decomposition of the molar excess heat capacity C p ,m E into electronic, magnetic and vibrational contributions yields the largest absolute values for C mag,m E . Molar excess entropies of mixing S m E at T = 298.15 K were also calculated from the heat capacity data. Despite considerable C mag,m E , the molar magnetic excess entropy at T = 298.15 K S mag,m E ( 298.15 K ) is only weakly negative for the solid solution (1.7 J · K−1 · mol−1to 2.7 J · K−1 · mol−1), because positive and negative contributions of C mag,m E / T as a function of temperature largely cancel each other between 0 K and 298.15 K. The molar electronic excess heat capacity C el,m E is positive for all temperatures and compositions, S el,m E ( 298.15 K ) thus shows a positive contribution with a maximum of 0.8 J · K−1 · mol−1 for Fo50Fa50. The molar vibrational excess entropy S vib,m E ( 298.15 K ) is also slightly positive for most members (maximum of 1.0 J · K−1 · mol−1 for Fo40Fa60). The resulting overall molar excess entropy, S tot,m E ( 298.15 K ) = S vib,m E ( 298.15 K ) + S el,m E ( 298.15 K ) + S mag,m E ( 298.15 K ) along the (forsterite + Fayalite) join is weakly negative within 2σ-uncertainty. Smoothed values of the molar heat capacity Cp,m, the molar entropies Δ 0 T S m , molar enthalpies Δ 0 T H m , and the molar Planck function Φm have been tabulated at selected temperatures for all olivine compositions.
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a low temperature calorimetric study of synthetic forsterite Fayalite mg2sio4 fe2sio4 solid solutions an analysis of vibrational magnetic and electronic contributions to the molar heat capacity and entropy of mixing
The Journal of Chemical Thermodynamics, 2007Co-Authors: Edgar Dachs, Charles A Geiger, Volker Von Seckendorff, Michael GrodzickiAbstract:The molar heat capacities (C-p,C-m)of a series of synthetic forsterite (Fo)-Fayalite (Fa), (Mg2SiO4 + Fe2SiO4), olivines have been measured between 5 K and 300 K on milligram-sized samples with the Physical Properties Measurement System (Quantum Design ((R))). Sharp, k-type heat capacity anomalies are observed in the Fe-rich compositions Fayalite, Fo(10)Fa(90), Fo(20)Fa(80), Fo(30)Fa(70), and Fo(40)Fa(60). The corresponding Neel temperatures T-N decrease linearly from 64.5 K in Fayalite to 32.8 K in Fo(40)Fa(60) following the relationship T-N = 79.02 . x(Fa) - 14.07. Fo(50)Fa(50) and Mg-richer olivines show weak broad features in the heat capacity data around 15 K to 20 K that decrease in magnitude with increasing forsterite content. In order to derive and separate molar electronic, magnetic and vibrational heat capacity contributions, C-el,C-m,C- C-mag,C-m,C- and C-vib,C-m from the experimental heat capacities (C-tot,C-m), we used a single-parametric phonon dispersion model to calculate C-vib,C-m for the solid-solution members and Fayalite. The C-el,C-m + C-mag,C-m(= C-tot,C-m - C-vib,C-m) contributions were fit to expressions describing a Schottky-type electronic anomaly and a paramagnetic-antiferromagnetic transition. For Fo(50)Fa(50) and Mg-richer olivines, our analysis of C-tot,C-m shows that also these compositions have a C-mag,C-m contribution with a maximum around 25 K. Decomposition of the molar excess heat capacity C-p,m(E) into electronic, magnetic and vibrational contributions yields the largest absolute values for C-mag,m,(E). Molar excess entropies of mixingp S-m(E) C-mag,m,(E). Molar magnetic excess entropies of mixing S-m(E) at T = 298.15 K were also calculated from the heat capacity data. Despite Considerable the molar magnetic excess entropy at T = 298.15 K S-mag,m(E) (298.15 K) is only weakly negative for the solid solution rnag,m mag,m of CE (1.7 J . K-1 mol(-1) to 2.7 J . K-1 . mol(-1)), because positive and negative contributions of C-el,m(E)/T as a function of temperature largely cancel each other between 0 K and 298.15 K. The molar electronic excess heat capacity C-el,m(E) is positive for all temperatures and compositions, S-vib,m(E) (298.15 K) thus shows a positive contribution with a maximum of 0.8 J . K-1 mol(-1) for Fo(50)Fa(50). The molar vibrational SE excess entropy S-vib,m(E) (298.15 K) is also slightly positive for most members (maximum of 1.0 J . K-1 . mol(-1) for Fo(40)Fa(60)). The resulting overall molar excess entropy, S-tot,m(E) (298.15 K) = S-vib,m(E) (298.15 K) + S-el,m(E) (298.15 K) + S-mag.m(E) (298.15 K) along the (forsterite + Fayalite) to Vi el magp TSttt, join is weakly negative within 2 sigma-uncertainty. Smoothed values of the molar heat capacity C-p,C-m,C- the molar entropies Delta(T)(0) S-m,S- molar enthalpies A T H., and the molar Planck function phi(m) have been tabulated at selected temperatures for all olivine compositions. (c) 2006 Elsevier Ltd. All rights reserved.
Michael Grodzicki - One of the best experts on this subject based on the ideXlab platform.
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a semi quantitative approach to derive the electric field gradient applied to synthetic Fayalite α fe2sio4 a reappraisal
European Journal of Mineralogy, 2012Co-Authors: Werner Lottermoser, Michael Grodzicki, Svenulf Weber, A Kirfel, Georg AmthauerAbstract:Experimental and calculated structure factors from a previous synchrotron diffraction measurement on synthetic Fayalite have been converted by an inverse Fourier transformation to difference electron (deformation) densities (DED). These were processed in a revised 3D-display program giving hyperareas of DED floating in space around the iron positions M1 and M2 within the Fayalite unit-cell and spanning a cluster size of 6 and 4 A, respectively. These relatively wide limits are due to the different site symmetries and had been proposed by earlier DFT (density functional theory) calculations. From the different hyperareas the supposed charges were integrated in space and processed to electric field gradients (EFG) on M1 and M2 using a point-charge model. The two EFGs were compared with respect to the system of crystallographic axes with those obtained from published single-crystal Mossbauer measurements (experimental EFGs), yielding excellent agreement within ±5° and surpassing even the DFT results. This study reports the procedure and the conditions of success of the underlying semi-quantitative method, which is halfway between theory (DFT) and experiment (diffractometry) and is promising valuable results on many other compounds. The term “nanoscope” for the graphical representation may be justified due to its high spatial resolution.
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a low temperature calorimetric study of synthetic forsterite Fayalite mg2sio4 fe2sio4 solid solutions an analysis of vibrational magnetic and electronic contributions to the molar heat capacity and entropy of mixing
The Journal of Chemical Thermodynamics, 2007Co-Authors: Edgar Dachs, Charles A Geiger, Volker Von Seckendorff, Michael GrodzickiAbstract:Abstract The molar heat capacities (Cp,m) of a series of synthetic forsterite (Fo)–Fayalite (Fa), (Mg2SiO4 + Fe2SiO4), olivines have been measured between 5 K and 300 K on milligram-sized samples with the Physical Properties Measurement System (Quantum Design®). Sharp, λ-type heat capacity anomalies are observed in the Fe-rich compositions Fayalite, Fo10Fa90, Fo20Fa80, Fo30Fa70, and Fo40Fa60. The corresponding Neel temperatures TN decrease linearly from 64.5 K in Fayalite to 32.8 K in Fo40Fa60 following the relationship TN = 79.02 · xFa − 14.07. Fo50Fa50 and Mg-richer olivines show weak broad features in the heat capacity data around 15 K to 20 K that decrease in magnitude with increasing forsterite content. In order to derive and separate molar electronic, magnetic and vibrational heat capacity contributions, Cel,m, Cmag,m, and Cvib,m from the experimental heat capacities (Ctot,m), we used a single-parametric phonon dispersion model to calculate Cvib,m for the solid-solution members and Fayalite. The Cel,m + Cmag,m(= Ctot,m − Cvib,m) contributions were fit to expressions describing a Schottky-type electronic anomaly and a paramagnetic–antiferromagnetic transition. For Fo50Fa50 and Mg-richer olivines, our analysis of Ctot,m shows that also these compositions have a Cmag,m contribution with a maximum around 25 K. Decomposition of the molar excess heat capacity C p ,m E into electronic, magnetic and vibrational contributions yields the largest absolute values for C mag,m E . Molar excess entropies of mixing S m E at T = 298.15 K were also calculated from the heat capacity data. Despite considerable C mag,m E , the molar magnetic excess entropy at T = 298.15 K S mag,m E ( 298.15 K ) is only weakly negative for the solid solution (1.7 J · K−1 · mol−1to 2.7 J · K−1 · mol−1), because positive and negative contributions of C mag,m E / T as a function of temperature largely cancel each other between 0 K and 298.15 K. The molar electronic excess heat capacity C el,m E is positive for all temperatures and compositions, S el,m E ( 298.15 K ) thus shows a positive contribution with a maximum of 0.8 J · K−1 · mol−1 for Fo50Fa50. The molar vibrational excess entropy S vib,m E ( 298.15 K ) is also slightly positive for most members (maximum of 1.0 J · K−1 · mol−1 for Fo40Fa60). The resulting overall molar excess entropy, S tot,m E ( 298.15 K ) = S vib,m E ( 298.15 K ) + S el,m E ( 298.15 K ) + S mag,m E ( 298.15 K ) along the (forsterite + Fayalite) join is weakly negative within 2σ-uncertainty. Smoothed values of the molar heat capacity Cp,m, the molar entropies Δ 0 T S m , molar enthalpies Δ 0 T H m , and the molar Planck function Φm have been tabulated at selected temperatures for all olivine compositions.
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a low temperature calorimetric study of synthetic forsterite Fayalite mg2sio4 fe2sio4 solid solutions an analysis of vibrational magnetic and electronic contributions to the molar heat capacity and entropy of mixing
The Journal of Chemical Thermodynamics, 2007Co-Authors: Edgar Dachs, Charles A Geiger, Volker Von Seckendorff, Michael GrodzickiAbstract:The molar heat capacities (C-p,C-m)of a series of synthetic forsterite (Fo)-Fayalite (Fa), (Mg2SiO4 + Fe2SiO4), olivines have been measured between 5 K and 300 K on milligram-sized samples with the Physical Properties Measurement System (Quantum Design ((R))). Sharp, k-type heat capacity anomalies are observed in the Fe-rich compositions Fayalite, Fo(10)Fa(90), Fo(20)Fa(80), Fo(30)Fa(70), and Fo(40)Fa(60). The corresponding Neel temperatures T-N decrease linearly from 64.5 K in Fayalite to 32.8 K in Fo(40)Fa(60) following the relationship T-N = 79.02 . x(Fa) - 14.07. Fo(50)Fa(50) and Mg-richer olivines show weak broad features in the heat capacity data around 15 K to 20 K that decrease in magnitude with increasing forsterite content. In order to derive and separate molar electronic, magnetic and vibrational heat capacity contributions, C-el,C-m,C- C-mag,C-m,C- and C-vib,C-m from the experimental heat capacities (C-tot,C-m), we used a single-parametric phonon dispersion model to calculate C-vib,C-m for the solid-solution members and Fayalite. The C-el,C-m + C-mag,C-m(= C-tot,C-m - C-vib,C-m) contributions were fit to expressions describing a Schottky-type electronic anomaly and a paramagnetic-antiferromagnetic transition. For Fo(50)Fa(50) and Mg-richer olivines, our analysis of C-tot,C-m shows that also these compositions have a C-mag,C-m contribution with a maximum around 25 K. Decomposition of the molar excess heat capacity C-p,m(E) into electronic, magnetic and vibrational contributions yields the largest absolute values for C-mag,m,(E). Molar excess entropies of mixingp S-m(E) C-mag,m,(E). Molar magnetic excess entropies of mixing S-m(E) at T = 298.15 K were also calculated from the heat capacity data. Despite Considerable the molar magnetic excess entropy at T = 298.15 K S-mag,m(E) (298.15 K) is only weakly negative for the solid solution rnag,m mag,m of CE (1.7 J . K-1 mol(-1) to 2.7 J . K-1 . mol(-1)), because positive and negative contributions of C-el,m(E)/T as a function of temperature largely cancel each other between 0 K and 298.15 K. The molar electronic excess heat capacity C-el,m(E) is positive for all temperatures and compositions, S-vib,m(E) (298.15 K) thus shows a positive contribution with a maximum of 0.8 J . K-1 mol(-1) for Fo(50)Fa(50). The molar vibrational SE excess entropy S-vib,m(E) (298.15 K) is also slightly positive for most members (maximum of 1.0 J . K-1 . mol(-1) for Fo(40)Fa(60)). The resulting overall molar excess entropy, S-tot,m(E) (298.15 K) = S-vib,m(E) (298.15 K) + S-el,m(E) (298.15 K) + S-mag.m(E) (298.15 K) along the (forsterite + Fayalite) to Vi el magp TSttt, join is weakly negative within 2 sigma-uncertainty. Smoothed values of the molar heat capacity C-p,C-m,C- the molar entropies Delta(T)(0) S-m,S- molar enthalpies A T H., and the molar Planck function phi(m) have been tabulated at selected temperatures for all olivine compositions. (c) 2006 Elsevier Ltd. All rights reserved.
Mikhail Yu Zolotov - One of the best experts on this subject based on the ideXlab platform.
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mn cr ages and formation conditions of Fayalite in cv3 carbonaceous chondrites constraints on the accretion ages of chondritic asteroids
Geochimica et Cosmochimica Acta, 2017Co-Authors: K Jogo, Tomoki Nakamura, Mikhail Yu Zolotov, Shigeru Wakita, Motoo Ito, S MessengerAbstract:Abstract Chondritic planetesimals are among the first planetary bodies that accreted inside and outside water snow line in the protoplanetary disk. CV3 carbonaceous chondrite parent body accreted relatively small amount of water ice, probably near the snow line, and experienced water-assisted metasomatic alteration that resulted in formation of diverse secondary minerals, including Fayalite (Fa 80–100 ). Chemical compositions of the CV3 Fayalite and its Mn–Cr isotope systematics indicate that it formed at different temperature (10–300 °C) and fluid pressure (3–300 bars) but within a relatively short period of time. Thermal modeling of the CV3 parent body suggests that it accreted ∼3.2–3.3 Ma after CV3 CAIs formation and had a radius of >110–150 km. The inferred formation age of the CV3 parent body is similar to that of the CM2 chondrite parent body that probably accreted beyond the snow line, but appears to have postdated accretion of the CO and ordinary chondrite parent bodies that most likely formed inside the snow line. The inferred differences in the accretion ages of chondrite parent bodies that formed inside and outside snow line are consistent with planetesimal formation by gravitational/streaming instability.
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Fayalite in the vigarano cv3 carbonaceous chondrite occurrences formation age and conditions
Earth and Planetary Science Letters, 2009Co-Authors: Kaori Jogo, Tomoki Nakamura, Takaaki Noguchi, Mikhail Yu ZolotovAbstract:Abstract We have performed petrographic characterization, 53Mn–53Cr age determination and thermodynamic stability evaluations of Fayalite in Vigarano meteorite that belongs to the reduced subgroup of CV3 chondrites. Vigarano is a breccia consisting of clasts which are separate chondrules surrounded by olivine-rich fine-grained materials. Four out of twenty three explored clasts contain Fayalites that represent materials of the Bali-like oxidized subgroup of CV3 chondrites. The Fayalites (Fa> 80) with grain sizes typically
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thermodynamic constraints on Fayalite formation on parent bodies of chondrites
Meteoritics & Planetary Science, 2006Co-Authors: Mikhail Yu Zolotov, M V Mironenko, Everett L ShockAbstract:Thermochemical equilibria are calculated in the multicomponent gas-solution-rock system in order to evaluate the formation conditions of Fayalite, (Fe0.881.0Mg0.120)2SiO4, Fa88100, in unequilibrated chondrites. Effects of temperature, pressure, water/rock ratio, rock composition, and progress of alteration are evaluated. The modeling shows that Fayalite can form as a minor secondary and transient phase with and without aqueous solution. Fayalite can form at temperatures below ~350 °C, but only in a narrow range of water/rock ratios that designates a transition between aqueous and metamorphic conditions. Pure Fayalite forms at lower temperatures, higher water/rock ratios, and elevated pressures that correspond to higher H2/H2O ratios. Lower pressure and water/rock ratios and higher temperatures favor higher Mg content in olivine. In equilibrium assemblages, Fayalite usually coexists with troilite, kamacite, magnetite, chromite, Ca-Fe pyroxene, and phyllosilicates. Formation of Fayalite can be driven by changes in temperature, pressure, H2/H2O, and water/rock ratios. However, in Fayalite-bearing ordinary and CV3 carbonaceous chondrites, the mineral could have formed during the aqueous-to-metamorphic transition. Dissolution of amorphous silicates in matrices and/or silica grains, as well as low activities of Mg solutes, favored aqueous precipitation of Fayalite. During subsequent metamorphism, Fayalite could have formed through the reduction of magnetite and/or dehydration of ferrous serpentine. Further metamorphism should have caused reductive transformation of Fayalite to Ca-Fe pyroxene and secondary metal, which is consistent with observations in metamorphosed chondrites. Although bulk compositions of matrices/chondrites have only a minor effect on Fayalite stability, specific alteration paths led to different occurrences, quantities, and compositions of Fayalite in chondrites.
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a low temperature calorimetric study of synthetic forsterite Fayalite mg2sio4 fe2sio4 solid solutions an analysis of vibrational magnetic and electronic contributions to the molar heat capacity and entropy of mixing
The Journal of Chemical Thermodynamics, 2007Co-Authors: Edgar Dachs, Charles A Geiger, Volker Von Seckendorff, Michael GrodzickiAbstract:Abstract The molar heat capacities (Cp,m) of a series of synthetic forsterite (Fo)–Fayalite (Fa), (Mg2SiO4 + Fe2SiO4), olivines have been measured between 5 K and 300 K on milligram-sized samples with the Physical Properties Measurement System (Quantum Design®). Sharp, λ-type heat capacity anomalies are observed in the Fe-rich compositions Fayalite, Fo10Fa90, Fo20Fa80, Fo30Fa70, and Fo40Fa60. The corresponding Neel temperatures TN decrease linearly from 64.5 K in Fayalite to 32.8 K in Fo40Fa60 following the relationship TN = 79.02 · xFa − 14.07. Fo50Fa50 and Mg-richer olivines show weak broad features in the heat capacity data around 15 K to 20 K that decrease in magnitude with increasing forsterite content. In order to derive and separate molar electronic, magnetic and vibrational heat capacity contributions, Cel,m, Cmag,m, and Cvib,m from the experimental heat capacities (Ctot,m), we used a single-parametric phonon dispersion model to calculate Cvib,m for the solid-solution members and Fayalite. The Cel,m + Cmag,m(= Ctot,m − Cvib,m) contributions were fit to expressions describing a Schottky-type electronic anomaly and a paramagnetic–antiferromagnetic transition. For Fo50Fa50 and Mg-richer olivines, our analysis of Ctot,m shows that also these compositions have a Cmag,m contribution with a maximum around 25 K. Decomposition of the molar excess heat capacity C p ,m E into electronic, magnetic and vibrational contributions yields the largest absolute values for C mag,m E . Molar excess entropies of mixing S m E at T = 298.15 K were also calculated from the heat capacity data. Despite considerable C mag,m E , the molar magnetic excess entropy at T = 298.15 K S mag,m E ( 298.15 K ) is only weakly negative for the solid solution (1.7 J · K−1 · mol−1to 2.7 J · K−1 · mol−1), because positive and negative contributions of C mag,m E / T as a function of temperature largely cancel each other between 0 K and 298.15 K. The molar electronic excess heat capacity C el,m E is positive for all temperatures and compositions, S el,m E ( 298.15 K ) thus shows a positive contribution with a maximum of 0.8 J · K−1 · mol−1 for Fo50Fa50. The molar vibrational excess entropy S vib,m E ( 298.15 K ) is also slightly positive for most members (maximum of 1.0 J · K−1 · mol−1 for Fo40Fa60). The resulting overall molar excess entropy, S tot,m E ( 298.15 K ) = S vib,m E ( 298.15 K ) + S el,m E ( 298.15 K ) + S mag,m E ( 298.15 K ) along the (forsterite + Fayalite) join is weakly negative within 2σ-uncertainty. Smoothed values of the molar heat capacity Cp,m, the molar entropies Δ 0 T S m , molar enthalpies Δ 0 T H m , and the molar Planck function Φm have been tabulated at selected temperatures for all olivine compositions.
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a low temperature calorimetric study of synthetic forsterite Fayalite mg2sio4 fe2sio4 solid solutions an analysis of vibrational magnetic and electronic contributions to the molar heat capacity and entropy of mixing
The Journal of Chemical Thermodynamics, 2007Co-Authors: Edgar Dachs, Charles A Geiger, Volker Von Seckendorff, Michael GrodzickiAbstract:The molar heat capacities (C-p,C-m)of a series of synthetic forsterite (Fo)-Fayalite (Fa), (Mg2SiO4 + Fe2SiO4), olivines have been measured between 5 K and 300 K on milligram-sized samples with the Physical Properties Measurement System (Quantum Design ((R))). Sharp, k-type heat capacity anomalies are observed in the Fe-rich compositions Fayalite, Fo(10)Fa(90), Fo(20)Fa(80), Fo(30)Fa(70), and Fo(40)Fa(60). The corresponding Neel temperatures T-N decrease linearly from 64.5 K in Fayalite to 32.8 K in Fo(40)Fa(60) following the relationship T-N = 79.02 . x(Fa) - 14.07. Fo(50)Fa(50) and Mg-richer olivines show weak broad features in the heat capacity data around 15 K to 20 K that decrease in magnitude with increasing forsterite content. In order to derive and separate molar electronic, magnetic and vibrational heat capacity contributions, C-el,C-m,C- C-mag,C-m,C- and C-vib,C-m from the experimental heat capacities (C-tot,C-m), we used a single-parametric phonon dispersion model to calculate C-vib,C-m for the solid-solution members and Fayalite. The C-el,C-m + C-mag,C-m(= C-tot,C-m - C-vib,C-m) contributions were fit to expressions describing a Schottky-type electronic anomaly and a paramagnetic-antiferromagnetic transition. For Fo(50)Fa(50) and Mg-richer olivines, our analysis of C-tot,C-m shows that also these compositions have a C-mag,C-m contribution with a maximum around 25 K. Decomposition of the molar excess heat capacity C-p,m(E) into electronic, magnetic and vibrational contributions yields the largest absolute values for C-mag,m,(E). Molar excess entropies of mixingp S-m(E) C-mag,m,(E). Molar magnetic excess entropies of mixing S-m(E) at T = 298.15 K were also calculated from the heat capacity data. Despite Considerable the molar magnetic excess entropy at T = 298.15 K S-mag,m(E) (298.15 K) is only weakly negative for the solid solution rnag,m mag,m of CE (1.7 J . K-1 mol(-1) to 2.7 J . K-1 . mol(-1)), because positive and negative contributions of C-el,m(E)/T as a function of temperature largely cancel each other between 0 K and 298.15 K. The molar electronic excess heat capacity C-el,m(E) is positive for all temperatures and compositions, S-vib,m(E) (298.15 K) thus shows a positive contribution with a maximum of 0.8 J . K-1 mol(-1) for Fo(50)Fa(50). The molar vibrational SE excess entropy S-vib,m(E) (298.15 K) is also slightly positive for most members (maximum of 1.0 J . K-1 . mol(-1) for Fo(40)Fa(60)). The resulting overall molar excess entropy, S-tot,m(E) (298.15 K) = S-vib,m(E) (298.15 K) + S-el,m(E) (298.15 K) + S-mag.m(E) (298.15 K) along the (forsterite + Fayalite) to Vi el magp TSttt, join is weakly negative within 2 sigma-uncertainty. Smoothed values of the molar heat capacity C-p,C-m,C- the molar entropies Delta(T)(0) S-m,S- molar enthalpies A T H., and the molar Planck function phi(m) have been tabulated at selected temperatures for all olivine compositions. (c) 2006 Elsevier Ltd. All rights reserved.
