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George R Rossman - One of the best experts on this subject based on the ideXlab platform.
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Allendeite sc4zr3o12 and hexamolybdenum mo ru fe two new minerals from an ultrarefractory inclusion from the Allende Meteorite
American Mineralogist, 2014Co-Authors: John R Beckett, George R RossmanAbstract:During a nanomineralogy investigation of the Allende Meteorite with analytical scanning electron microscopy, two new minerals were discovered; both occur as micro- to nano-crystals in an ultrarefractory inclusion, ACM-1. They are Allendeite, Sc_4Zr_3O_(12), a new Sc- and Zr-rich oxide; and hexamolybdenum (Mo,Ru,Fe,Ir,Os), a Mo-dominant alloy. Allendeite is trigonal, R3, ɑ = 9.396, c = 8.720, V = 666.7 A^3, and Z = 3, with a calculated density of 4.84 g/cm^3 via the previously described structure and our observed chemistry. Hexamolybdenum is hexagonal, P6_3/mmc, ɑ = 2.7506, c = 4.4318 A, V = 29.04 A^3, and Z = 2, with a calculated density of 11.90 g/cm^3 via the known structure and our observed chemistry. Allendeite is named after the Allende Meteorite. The name hexamolybdenum refers to the symmetry (primitive hexagonal) and composition (Mo-rich). The two minerals reflect conditions during early stages of the formation of the Solar System. Allendeite may have been an important ultrarefractory carrier phase linking Zr-,Sc-oxides to the more common Sc-,Zr-enriched pyroxenes in Ca-Al-rich inclusions. Hexamolybdenum is part of a continuum of high-temperature alloys in Meteorites supplying a link between Os- and/or Ru-rich and Fe-rich meteoritic alloys. It may be a derivative of the former and a precursor of the latter.
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grossmanite cati3 alsio6 a new pyroxene from the Allende Meteorite
American Mineralogist, 2009Co-Authors: George R RossmanAbstract:Grossmanite, Ca(Ti3+,Mg,Ti4+)AlSiO6 with an end-member formula CaTi3+AlSiO6, is a new member of the Ca clinopyroxene group, where the trivalent cations are dominant in the M1 site with Ti3+ being the dominant trivalent cation. It occurs as micrometer-sized crystals along with spinel and perovskite in a melilite host in Ca-, Al-rich refractory inclusions from the Allende Meteorite. The mean chemical composition determined by electron microprobe analysis of the type material is (wt%) SiO2 27.99, Al2O3 24.71, CaO 24.58, Ti2O3 10.91, TiO2 6.68, MgO 4.45, Sc2O3 0.43, V2O3 0.19, ZrO2 0.13, FeO 0.08, Cr2O3 0.03, sum 100.20. Its empirical formula calculated on the basis of 6 O atoms is Ca1.00[(Ti0.353+Al0.18Sc0.01V0.013+)∑0.55Mg0.25Ti0.194+]∑1.00(Si1.07Al0.93)∑2.00O6. Grossmanite is monoclinic, C 2/ c; a = 9.80 A, b = 8.85 A, c = 5.36 A, β = 105.62°, V = 447.70 A3, and Z = 4. Its electron back-scatter diffraction pattern is an excellent match to that of Ti3+-rich pyroxene with the C 2/ c structure. The five strongest calculated X-ray powder diffraction lines are [ d spacing in A, ( I ), hkl ] 2.996 (100) (221), 2.964 (31) (310), 2.581 (42) (002), 2.600 (28) (131), 2.535 (47) (221). The name is for Lawrence Grossman, a cosmochemist at the University of Chicago.
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Grossmanite, CaTi3+AlSiO6, a new pyroxene from the Allende Meteorite
American Mineralogist, 2009Co-Authors: Chi Ma, George R RossmanAbstract:Grossmanite, Ca(Ti3+,Mg,Ti4+)AlSiO6 with an end-member formula CaTi3+AlSiO6, is a new member of the Ca clinopyroxene group, where the trivalent cations are dominant in the M1 site with Ti3+ being the dominant trivalent cation. It occurs as micrometer-sized crystals along with spinel and perovskite in a melilite host in Ca-, Al-rich refractory inclusions from the Allende Meteorite. The mean chemical composition determined by electron microprobe analysis of the type material is (wt%) SiO2 27.99, Al2O3 24.71, CaO 24.58, Ti2O3 10.91, TiO2 6.68, MgO 4.45, Sc2O3 0.43, V2O3 0.19, ZrO2 0.13, FeO 0.08, Cr2O3 0.03, sum 100.20. Its empirical formula calculated on the basis of 6 O atoms is Ca1.00[(Ti0.353+Al0.18Sc0.01V0.013+)∑0.55Mg0.25Ti0.194+]∑1.00(Si1.07Al0.93)∑2.00O6. Grossmanite is monoclinic, C 2/ c; a = 9.80 A, b = 8.85 A, c = 5.36 A, β = 105.62°, V = 447.70 A3, and Z = 4. Its electron back-scatter diffraction pattern is an excellent match to that of Ti3+-rich pyroxene with the C 2/ c structure. The five strongest calculated X-ray powder diffraction lines are [ d spacing in A, ( I ), hkl ] 2.996 (100) (221), 2.964 (31) (310), 2.581 (42) (002), 2.600 (28) (131), 2.535 (47) (221). The name is for Lawrence Grossman, a cosmochemist at the University of Chicago.
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davisite cascalsio6 a new pyroxene from the Allende Meteorite
American Mineralogist, 2009Co-Authors: George R RossmanAbstract:Davisite, ideally CaScAlSiO_6, is a new member of the Ca clinopyroxene group, where Sc^(3+) is dominant in the M1 site. It occurs as micro-sized crystals along with perovskite and spinel in an ultra-refractory inclusion from the Allende Meteorite. The mean chemical composition determined by electron microprobe analysis is (wt%) SiO_2 26.24, CaO 23.55, Al_2O_3 21.05, Sc_2O_3 14.70, TiO_2 (total) 8.66, MgO 2.82, ZrO_2 2.00, Y_2O_3 0.56, V_2O_3 0.55, FeO 0.30, Dy_2O_3 0.27, Gd_2O_3 0.13, Er_2O_3 0.08, sum 100.91. Its empirical formula calculated on the basis of 6 O atoms is Ca_(0.99)(Sc_(0.50)Ti^(3+)0.16^(Mg)0.16Ti^(4+)0.10 Zr_(0.04)V^(3+)_(0.02)Fe^(2+)_(0.01)Y_(0.01))_(∑1.00)(Si_(1.03)Al_(0.97))_(∑2).00O_6. Davisite is monoclinic, C2/c; a = 9.884 A, b = 8.988 A, c = 5.446 A, β =105.86°, V = 465.39 A^3, and Z = 4. Its electron back-scattered diffraction pattern is an excellent match to that of synthetic CaScAlSiO6 with the C2/c structure. The strongest calculated X-ray powder diffraction lines are [d spacing in A (I) (hkl)]: 3.039 (100) (221), 2.989 (31) (310), 2.943 (18) (311), 2.619 (40) (002), 2.600 (26) (131), 2.564 (47) (221), 2.159 (18) (331), 2.137 (15) (421), 1.676 (20) (223), and 1.444 (18) (531). The name is for Andrew M. Davis, a cosmochemist at the University of Chicago, Illinois.
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tistarite ti2o3 a new refractory mineral from the Allende Meteorite
American Mineralogist, 2009Co-Authors: George R RossmanAbstract:Tistarite, ideally Ti_2O_3, is a new member of the corundum-hematite group. It is found as one subhedral crystal in a cluster of micrometer-sized refractory grains along with khamrabaevite (TiC), rutile, and corundum crystals within a chondrule from the Allende Meteorite. The mean chemical composition determined by electron microprobe analysis is (wt%) Ti_2O_3 94.94, MgO 2.06, Al_2O_3 1.50, ZrO_2 0.44, FeO 0.24, CaO 0.10, Cr_2O_3 0.06, sum 99.34. The empirical formula calculated on the basis of 3 O atoms is (Ti^(3+)_(1.90)Mg_(0.07)Al_(0.04)Zr_(0.01))∑_(2.02)O_3. Tistarite is rhombohedral, R3–c; a = 5.158 A, c = 13.611 A, V = 313.61 A^3, and Z = 6. Its electron back-scatter diffraction pattern matches that of synthetic Ti_2O_3 with the R3–c structure. The strongest calculated X-ray powder diffraction lines from the synthetic Ti_2O_3 data are [d spacing in A (I) hkl]: 3.734 (84) (012), 2.707 (88) (104), 2.579 (90) (110), 2.242 (38) (113), 1.867 (33) (024), 1.703 (100) (116), 1.512 (28) (214), 1.489 (46) (300), 1.121 (20) (226), 0.896 (25) (416). The mineral is named after the composition "Ti" and the word "star," implying that this new refractory mineral is among the first solids formed in the solar system.
Junichi Matsuda - One of the best experts on this subject based on the ideXlab platform.
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an attempt to characterize phase q noble gas raman spectroscopy and transmission electron microscopy in residues prepared from the Allende Meteorite
Geochimica et Cosmochimica Acta, 2010Co-Authors: Junichi Matsuda, Sachiko Amari, Kazuhiko Morishita, Masayuki Nara, Hidetomo Tsukamoto, Chie Miyakawa, Tetsuya Uchiyama, Seiji TakedaAbstract:We have prepared a HF–HCl residue and its oxidized residue of the Allende Meteorite and have measured the elemental concentrations and the isotopic compositions of noble gases. In the HF–HCl reside, noble gases are enriched in colloidal fraction compared to the non-colloidal fraction by a factor of 2–4. The heavy noble gases were evidently lost after the oxidization, indicating that phase Q (carrier of planetary heavy noble gases) was removed by the oxidation. The Raman spectroscopic parameters show that the colloidal fraction of the HF–HCl residue is more amorphous compared to the non-colloidal fraction. As the ion irradiation converts carbon into a more amorphous form, our result indicates that the “plasma model” is more plausible than the “labyrinth model” as the origin of phase Q. TEM (Transmission Electron Microscope) observations also show such a trace of ion irradiation. While the TEM observations did not show any large difference between the HF–HCl residue and its oxidized residue, the Raman spectroscopic parameters changed discretely resulting from the oxidization. This observation indicates that the oxidization not only dissolved and removed oxidized carbon, but also changed the carbon structure itself to a more amorphous (disordered) state. The Raman spectroscopic results indicate the possibility that release of Q-gas during oxidation is not accompanied by mass loss and that the release of Q-gas simply resulted from rearrangement of carbon structure during oxidation.
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raman spectroscopic study of the noble gas carrier q in the Allende Meteorite
Geochemical Journal, 2009Co-Authors: Junichi Matsuda, Kazuhiko Morishita, Masayuki Nara, Sachiko AmariAbstract:We report Raman spectroscopic results of four density-separated fractions of a floating fraction (material similar to HF-HCl residues enriched in heavy noble gases) of the Allende Meteorite. The Raman analyses were performed at two laser powers of 0.5 mW and 2-6 mW with the excitation wavelength of 532 nm. The typical Raman spectra of carbon were observed for all the samples, but these carbonaceous materials were very sensitive to the laser power at the analysis. The Raman parameters except for the intensity ratio of D band and G band are similar in all the fractions at the low laser power, but they changed at the high laser power in a different manner, probably due to the different degree of laser-induced heating. Our findings are that phase Q (the carrier of noble gas of the normal isotopic composition in Meteorites) is enriched in the graphitic carbon having larger domain size compared to the major carbon in Allende and that this carbon is most affected by the laser heating.
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an attempt to separate q from the Allende Meteorite by physical methods
Geochimica et Cosmochimica Acta, 2003Co-Authors: Sachiko Amari, Shiho Zaizen, Junichi MatsudaAbstract:Abstract In order to characterize the planetary noble gas carrier Q, we separated a Q-rich floating fraction from the Allende Meteorite into ten fractions by a combination of colloidal and density separations. All five noble gases in the separated fractions were analyzed by pyrolysis in 600 and 1600°C temperature steps. Half of Q in the floating fraction is concentrated in the fraction C1-8D with the density of 1.65 ± 0.04 g/cm 3 . All the separated fractions show similar isotopic ratios except for 40 Ar/ 36 Ar ratios. C1-8D has the lowest 38 Ar/ 36 Ar and 40 Ar/ 36 Ar ratios (0.18784 ± 0.00020 and 4.36 ± 0.15, respectively) in the 1600°C fraction, confirming that the fraction is enriched in Q. Most grains in C1-8D are carbonaceous with small amounts of F and O. These results imply either that the density of Q is 1.65 ± 0.04 g/cm 3 or that Q preferentially sticks to matter of that density. All the separates have similar Q to diamond ratios, indicating that Q and diamond are closely associated.
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purely physical separation of a small fraction of the Allende Meteorite that is highly enriched in noble gases
Meteoritics & Planetary Science, 1999Co-Authors: Junichi Matsuda, Sachiko Amari, Keisuke NagaoAbstract:~~ Abstract-Fine material that floats during freeze-thaw disaggregation of the Allende Meteorite is greatly enriched in noble gases compared to the bulk Meteorite. Not only the elemental concentrations, but also most isotopic ratios of the noble gases in this fraction, strongly suggest that this material is very similar to the gas- rich carbonaceous residue isolated from the bulk Meteorite by chemical treatment. The only significant difference in noble gas signature between our separated fraction and the chemical residues is that the 129Xe/132Xe ratio in the former is significantly lower than that in the latter, which suggests readsorption of 129Xe released from the dissolved minerals during the chemical treatment. This is the first time that a gas- rich residue of a Meteorite has been separated by a purely physical method alone. We also show that noble gases in phase Q and presolar diamond may be separable physically, although both are closely associated.
Edward D Young - One of the best experts on this subject based on the ideXlab platform.
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mg isotope heterogeneity in the Allende Meteorite measured by uv laser ablation mc icpms and comparisons with o isotopes
Geochimica et Cosmochimica Acta, 2002Co-Authors: Edward D Young, Albert Galy, Nick S BelshawAbstract:First results from a new UV laser ablation MC-ICPMS method for measuring Mg isotope ratios in situ in meteoritical materials show that there are mass-dependent variations in 25 Mg and 26 Mg up to 1.5 ‰ per amu in chondrules and 0.3‰ per amu in a CAI from the Allende Meteorite. In both cases the mass-dependent fractionation is associated with alteration. Comparisons with laser ablation O isotope data indicate that incorporation of pre-existing grains of forsterite with distinct Mg and O isotopic compositions and post-formation alteration both contributed to the variability in Mg isotope ratios in the chondrules, resulting in a correlation between high 25 Mg and low 17 O. The laser ablation analyses of the CAI show that high-precision determinations of both 25 Mg and 26 Mg can be used to discriminate features of the 26 Al- 26 Mg isotope system that are relevant to chronology from those that result from element mobility. Copyright © 2002 Elsevier Science Ltd
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uv laser ablation and irm gcms microanalysis of 18o 16o and 17o 16o with application to a calcium aluminium rich inclusion from the Allende Meteorite
Geochimica et Cosmochimica Acta, 1998Co-Authors: Edward D Young, David W Coutts, D KapitanAbstract:Abstract Analyses of 18O/16O and 17O/16O in silicate and oxide minerals by UV laser ablation of 100 × 80 × 50 μm sample pits combined with irm-GCMS yield precision and accuracy similar to that of conventional methods. This represents a 100-fold reduction in minimum size relative to other fluorination methods based on gas-source mass spectrometry and enables high-precision in-situ intracrystalline analysis of silicate minerals. Analyses of almandine, forsterite, and schorl of known isotopic compositions indicate an analytical precision of ±0.3‰ (1σ) in δ18O and ±0.4 in δ17O with an accuracy of similar magnitude. Application to meteoritic samples is demonstrated by in-situ analysis of pyroxene and melilite from a type B CAI inclusion from the Allende Meteorite. The CAI data adhere to the carbonaceous chondrite anhydrous mineral line defined by conventional macroscopic fluorination methods and demonstrate that non-mass dependent differences of 1‰ amu−1 are discernible. The unique combination of analytical and spatial resolution afforded by the new UV laser microprobe will allow high-precision mapping of the distribution of anomalous oxygen in minerals from calcium-aluminum-rich inclusions on a previously unattainable scale.
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UV laser ablation and irm-GCMS microanalysis of 18O/16O and 17O/16O with application to a calcium-aluminium-rich inclusion from the Allende Meteorite
Geochimica et Cosmochimica Acta, 1998Co-Authors: Edward D Young, David W Coutts, D KapitanAbstract:Abstract Analyses of 18O/16O and 17O/16O in silicate and oxide minerals by UV laser ablation of 100 × 80 × 50 μm sample pits combined with irm-GCMS yield precision and accuracy similar to that of conventional methods. This represents a 100-fold reduction in minimum size relative to other fluorination methods based on gas-source mass spectrometry and enables high-precision in-situ intracrystalline analysis of silicate minerals. Analyses of almandine, forsterite, and schorl of known isotopic compositions indicate an analytical precision of ±0.3‰ (1σ) in δ18O and ±0.4 in δ17O with an accuracy of similar magnitude. Application to meteoritic samples is demonstrated by in-situ analysis of pyroxene and melilite from a type B CAI inclusion from the Allende Meteorite. The CAI data adhere to the carbonaceous chondrite anhydrous mineral line defined by conventional macroscopic fluorination methods and demonstrate that non-mass dependent differences of 1‰ amu−1 are discernible. The unique combination of analytical and spatial resolution afforded by the new UV laser microprobe will allow high-precision mapping of the distribution of anomalous oxygen in minerals from calcium-aluminum-rich inclusions on a previously unattainable scale.
Keiji Misawa - One of the best experts on this subject based on the ideXlab platform.
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magnesium isotopic fractionations in barred olivine chondrules from the Allende Meteorite
Meteoritics & Planetary Science, 2000Co-Authors: Keiji Misawa, Takashi FujitaAbstract:— The Mg-isotopic compositions in five barred olivine (BO) chondrules, one coarse-grained rim of a BO chondrule, a relic spinel in a BO chondrule, one skeletal olivine chondrule similar to BO chondrules in mineralogy and composition, and two non-BO chondrules from the Allende Meteorite have been measured by thermal ionization mass spectrometry. The Mg isotopes are not fractionated and are within terrestrial standard values (±2.0%o per amu) in seven of the eight analyzed ferromagnesian chondrules. A clump of relic spinel grain and its host BO chondrule R-11 give well-resolvable Mg fractionations that show an enrichment of the heavier isotopes, up to +2.5%‰ per amu. The Mg-isotopic compositions of coarse-grained rim are identical to those of the host chondrule with BO texture. The results imply that ferromagnesian and refractory precursor components of the Allende chondrule may have been formed from isotopically heterogeneous reservoirs. In the nebula region where Allende chondrules formed, recycling of chondrules and multiple high-temperature heating did not significantly alter the chemical and isotopic memory of earlier generations. Chemical and isotopic characteristics of refractory precursors of carbonaceous chondrite chondrules and CAIs are more closely related than previously thought. One of the refractory chondrule precursors of CV Allende is enriched in the heavier Mg isotopes and different from those of more common ferromagnesian chondrule precursors. The most probable scenario at the location where chondrule R-11 formed is as follows. Before chondrule formation, several high-temperature events occurred and then RPMs, refractory oxides, and silicates condensed from the nebular gas in which Mg isotopes were fractionated. Then, this CAI was transported into the chondrule formation region and mixed with more common, ferromagnesian precursors with normal Mg isotopes, and formed the BO chondrule. Because Mg isotope heterogeneity among silicates and spinel are found in some CAIs (Esat and Taylor, 1984), we cannot rule out the possibility that Mg isotopes of a melted portion of the refractory precursor (i.e., outer portion of CAI) are normal or enriched in the light isotope. Magnesium isotopes in the R-11 host are also enriched in the heavier isotopes, +2.5%o per amu, which suggests that effects of isotopic heterogeneity among silicates and spinel, if they existed, are not considered to be large. It is possible that CAI precursor silicates partially dissolved during the chondrule forming event, contributing Mg to the melt and producing a uniform Mg-isotopic signature but enriched in the heavier Mg isotopes, +2.5%‰ per amu. Most Mg isotopes in more common ferromagnesian chondrules represent normal chondritic material. Chemical and Mg-isotopic signatures formed during nebular fractionations were not destroyed during thermal processes that formed the chondrule, and these were partly preserved in relic phases. Recycling of Allende chondrules and multiple heating at high temperature did not significantly alter the chemical and Mg-isotopic memory of earlier generations.
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a relict refractory inclusion in a ferromagnesian chondrule from the Allende Meteorite
Nature, 1994Co-Authors: Keiji Misawa, Takashi FujitaAbstract:CARBONACEOUS chondrites such as the Allende Meteorite are composed of abundant ferromagnesian chondrules and (Ca, Al)-rich inclusions (CAIs) embedded in a fine-grained matrix. The chondrules were formed by melting of pre-existing solid precursor materials1, whereas CAIs formed either by direct condensation from the nebular gas or by high-temperature processing of solids in the nebula2. These two components usually appear as discrete objects in chondrites, and are believed3 to have formed independently before agglomeration of the chondrite parent bodies. However, elemental analyses of some Al-rich chondrules4–8 suggest that there was a refractory component—such as CAIs—in the chondrule precursor material. We report here the discovery of a ferromagnesian chondrule from the Allende Meteorite that contains an intact CAI fragment. This finding confirms that some CAIs coexisted with the precursor material of ferromagnesian chondrules, and helps to constrain the timing of the formation events of these two components.
R D Loss - One of the best experts on this subject based on the ideXlab platform.
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the isotopic composition of zinc palladium silver cadmium tin and tellurium in acid etched residues of the Allende Meteorite
Geochimica et Cosmochimica Acta, 1990Co-Authors: R D Loss, K J R Rosman, J R De LaeterAbstract:The isotopic and elemental abundances of Zn, Pd, Ag, Cd, Sn, and Te have been measured in three acid-resistant residues extracted from the Allende Meteorite. High-efficiency, low-contamination ion-exchange procedures were developed to separate and purify the nanogram amounts of these elements present. Elemental-abundance determinations performed by Mass Spectrometric Isotope Dilution agree with previously published work for similarly derived residues. No isotope anomalies similar to those found for Xe (Xe-HL) in these samples were detected for any of these elements, which is consistent with the residues not being derived directly from the Xe-HL carriers. The lack of major Te-isotope anomalies does not support earlier reports of {sup 126}Te and {sup 130}Te excesses which were measured by neutron activation in similar samples. Small excesses were detected in the minor isotopes of Sn and Te, but these may be due to measurement problems associated with the small ion currents obtained for these samples. Two of the residue solutions contain Cd with up to several percent excesses for {sup 106}Cd and {sup 108}Cd. Interpretations of these results are limited by the unknown nature of the carrier minerals in the residues but may indicate the presence of a p-process component in Allende residues.
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zinc isotope anomalies in Allende Meteorite inclusions
The Astrophysical Journal, 1990Co-Authors: R D Loss, G W LugmairAbstract:The isotopic compositions of Zn, Cr, Ti, and Ca have been measured in a number of CAIs from the Allende Meteorite. The aim was to test astrophysical models which predict large excesses of Zn-66 to accompany excesses in the neutron-rich isotopes of Ca, Ti, Cr, and Ni. Some of the CAIs show clearly resolved but small excesses for Zn-66 which are at least an order of magnitude smaller than predicted. This result may simply reflect the volatility and chemical behavior of Zn as compared to the other (more refractory) anomalous elements found in these samples. Alternatively, revision of parameters and assumptions used for the model calculations may be required. 34 refs.
