Magnetic study of magnetite in the Tagish Lake meteorite

Abstract— The saturation magnetization, saturation remanent magnetization, the coercive, and remanent coercive force were determined at room and liquid nitrogen temperatures for three pieces of the Tagish Lake meteorite. The results are compared to similar data for four other chondrites (Allende, Murray, Orgueil, and Murchison). The data suggests that the Tagish Lake meteorite is magnetically homogeneous, and is not as magnetically hard as the comparison chondrites. The magnetization measurements indicate that it contains about 10–11% multi‐domain magnetite. Magnetic susceptibility measurements on all the samples from 77 K to room temperature showed a Verwey transition for all the samples which contain a significant amount of multi‐domain magnetite. The coercive force data further indicate that the magnetite in Tagish Lake is multi‐domain and that the grain size is small and approximately 4–9 μm.     

Amino acids in the Tagish Lake meteorite

Abstract— High‐performance liquid chromatography (HPLC) based amino acid analysis of a Tagish Lake meteorite sample recovered 3 months after the meteorite fell to Earth have revealed that the amino acid composition of Tagish Lake is strikingly different from that of the CM and CI carbonaceous chondrites. We found that the Tagish Lake meteorite contains only trace levels of amino acids (total abundance = 880 ppb), which is much lower than the total abundance of amino acids in the CI Orgueil (4100 ppb) and the CM Murchison (16 900 ppb). Because most of the same amino acids found in the Tagish Lake meteorite are also present in the Tagish Lake ice melt water, we conclude that the amino acids detected in the meteorite are terrestrial contamination. We found that the exposure of a sample of Murchison to cold water lead to a substantial reduction over a period of several weeks in the amount of amino acids that are not strongly bound to the meteorite matrix. However, strongly bound amino acids that are extracted by direct HCl hydrolysis are not affected by the leaching process. Thus even if there had been leaching of amino acids from our Tagish Lake meteorite sample during its 3 month residence in Tagish Lake ice and melt water, a Murchison type abundance of endogenous amino acids in the meteorite would have still been readily detectable. The low amino acid content of Tagish Lake indicates that this meteorite originated from a different type of parent body than the CM and CI chondrites. The parent body was apparently devoid of the reagents such as aldehyldes/ketones, HCN and ammonia needed for the effective abiotic synthesis of amino acids. Based on reflectance spectral measurements, Tagish Lake has been associated with P‐ or D‐type asteroids. If the Tagish Lake meteorite was indeed derived from these types of parent bodies, our understanding of these primitive asteroids needs to be reevaluated with respect to their potential inventory of biologically important organic compounds.     

Diradicaloids in the insoluble organic matter from the Tagish Lake meteorite: Comparison with the Orgueil and Murchison meteorites

Abstract— The radicals in the insoluble organic matter (IOM) from the Tagish Lake meteorite were studied by electron paramagnetic resonance and compared to those existing in the Orgueil and Murchison meteorites. As in the Orgueil and Murchison meteorites, the radicals in the Tagish Lake meteorite are heterogeneously distributed and comprise a substantial amount (?42%) of species with a thermally accessible triplet state and with the same singlet‐triplet gap, ΔE ?0.1 eV, as in the Orgueil and Murchison meteorites. These species were identified as diradicaloid moieties. The existence of similar diradicaloid moieties in three different carbonaceous chondrites but not in terrestrial IOM strongly suggests that these moieties could be “fingerprints” of the extraterrestrial origin of meteoritic IOM and markers of its synthetic pathway before its inclusion into a parent body.     

Bulk mineralogical changes of hydrous micrometeorites during heating in the upper atmosphere at temperatures below 1000 °C

Abstract— Small particles 200 μm in diameter from the hydrous carbonaceous chondrites Orgueil CI, Murchison CM2, and Tagish Lake were experimentally heated for short durations at subsolidus temperatures under controlled ambient pressures in order to examine the bulk mineralogical changes of hydrous micrometeorites during atmospheric entry. The three primitive meteorites consist mainly of various phyllosilicates and carbonates that are subject to decomposition at low temperatures, and thus the brief heating up to 1000 °C drastically changed the mineralogy. Changes included shrinkage of interlayer spacing of saponite due to loss of molecular water at 400–600 °C, serpentine and saponite decomposition to amorphous phases at 600 and 700 °C, respectively, decomposition of Mg‐Fe carbonate at 600 °C, recrystallization of secondary olivine and Fe oxide or metal at 700–800 °C, and recrystallization of secondary low‐Ca pyroxene at 800 °C. The ambient atmospheric pressures controlled species of secondary Fe phase: taenite at pressures lower than 10^?2 torr, magnesiowüstite from 10^?3 to 10^?1 torr, and magnetite from 10^?2 to 1 torr. The abundance of secondary low‐Ca pyroxene increases in the order of Murchison, Orgueil, and Tagish Lake, and the order corresponds to saponite abundance in samples prior to heating. Mineralogy of the three unmelted micrometeorites F96CI024, kw740052, and kw740054 were investigated in detail in order to estimate heating conditions. The results showed that they might have come from different parental objects, carbonaterich Tagish Lake type, carbonate‐poor Tagish Lake or CI type, and CM type, respectively, and experienced different peak temperatures, 600, 700, and 800?900 °C, respectively, at 60–80 km altitude upon atmospheric entry.     

Petrography and mineral chemistry of the anhydrous component of the Tagish Lake carbonaceous chondrite

Abstract— Most studies of Tagish Lake have considered features that were either strongly affected by or formed during the extensive hydrous alteration experienced by this meteorite. This has led to some ambiguity as to whether Tagish Lake should be classified a CI, a CM, or something else. Unlike previous workers, we have focused upon the primary, anhydrous component of Tagish Lake, recovered through freeze‐thaw disaggregation and density separation and located by thin section mapping. We found many features in common with CMs that are not observed in CIs. In addition to the presence of chondrules and refractory forsterite (which distinguish Tagish Lake from the CIs), we found hibonite‐bearing refractory inclusions, spinel‐rich inclusions, forsterite aggregates, Cr‐, Al‐rich spinel, and accretionary mantles on many clasts, which clearly establishes a strong link between Tagish Lake and the CM chondrites. The compositions of isolated olivine crystals in Tagish Lake are also like those found in CMs. We conclude that the anhydrous inclusion population of Tagish Lake was, originally, very much like that of the known CM chondrites and that the inclusions in Tagish Lake are heavily altered, more so than even those in Mighei, which are more heavily altered than those in Murchison.     

Mineralogy of Tagish Lake: An ungrouped type 2 carbonaceous chondrite

Abstract— In this paper we describe the recovery, handling and preliminary mineralogical investigation of the Tagish Lake meteorite. Tagish Lake is a type 2 carbonaceous chondrite which bears similarities to CI1 and CM chondrite groups, but is distinct from both. Abundant phyllosilicates as well as chondrules (however sparse) and common olivine grains in the matrix preclude any other classification. The bulk density of Tagish Lake (1.67 g/cc) is far lower than CI or CM chondrites (2.2‐2.3 and 2.6‐2.9 g/cc, respectively), or any other meteorite for that matter. We have identified two lithologies: a dominant carbonate‐poor lithology and a less‐abundant carbonate‐rich lithology. The meteorite is a breccia at all scales. We have noted similarities between Tagish Lake and some clasts within the enigmatic meteorite Kaidun; possibly there are genetic relationships here worth exploring. In the paper we describe a clast of CM1 material within Tagish Lake which is very similar to a major lithology in Kaidun.     

Comparison of the trace element composition of Tagish Lake with other primitive carbonaceous chondrites

Abstract— A meteorite fall on 2000 January 18 was detected by U.S. Defense Department satellites which established its pre‐impact orbit. Fresh samples were collected from frozen Tagish Lake in British Columbia a week later and some properties of these samples reveal it to be a unique meteorite. We characterized Tagish Lake and 8 other samples using inductively‐coupled plasma mass spectrometry and radiochemical neutron activation analysis: data for 47 elements reveal that each of 9 carbonaceous chondrites of different type exhibit the Orgueil‐normalized plateaus expected for members of such types. Trends evident in Tagish Lake differ from all other carbonaceous chondrites, including CI and CM. Samples of Tagish Lake collected later show similar patterns affected by weathering.     

Mineralogical and spectroscopic investigation of the Tagish Lake carbonaceous chondrite by X‐ray diffraction and infrared reflectance spectroscopy

Abstract– We have carried out a sample‐correlated spectroscopic and mineralogical investigation of samples from seven different collection sites of the Tagish Lake C2 chondrite. Rietveld refinement of high‐resolution powder X‐ray diffraction (XRD) data was used to determine quantitative major mineral abundances. Thermal infrared (400–4500 cm⁻¹, 2.2–25.0 μm) spectra of the same samples were obtained using diffuse (biconical) reflectance infrared Fourier transform spectroscopy (DRIFTS). Our results are in good agreement with previous studies of the mineralogy of the Tagish Lake meteorite; we find however that Tagish Lake is more varied in major mineralogy than has previously been reported. In particular, we observed two new distinct lithologies, an inclusion‐poor magnetite‐ and sulfide‐rich lithology, and a carbonate‐rich, siderite‐dominated lithology in addition to the previously documented carbonate‐rich and carbonate‐poor lithologies. Grain density for each Tagish Lake sample was calculated from the measured mineral modal abundances and known mineral densities. For powders from three originally intact inclusion‐rich samples, the calculated grain density is 2.77 ± 0.05 g cm⁻³, in excellent agreement with those reported in the literature for other intact inclusion‐rich Tagish Lake samples. Tagish Lake disaggregated samples have a significantly higher calculated grain density due to their lower saponite‐serpentine content, likely a result of mineral separation in the meltwater holes from which they were collected; the disaggregated samples may not therefore adequately represent bulk samples of the Tagish Lake meteorite. The predominance of very fine‐grained material in the Tagish Lake samples investigated in this study is expected to produce infrared spectra representative of asteroidal regolith. Gypsum and talc have been found by XRD in powders from the inclusion‐rich, intact Tagish Lake samples in this study, and may have been present in the parent body; if present, these hydrous sulfates would complicate the interpretation of possible hydrated mineral features in asteroid infrared spectra.     

Multi-technique investigation reveals new mineral, chemical, and textural heterogeneity in the Tagish Lake C2 chondrite

The Tagish Lake meteorite, an ungrouped C2 chondrite that is related to CI and CM chondrites, is a heterogeneous accretionary breccia with several distinct lithologies that, in bulk, are thought to represent the first known sample of a primitive carbonaceous D-type asteroid. Textural and chemical zoning of clasts and matrix have been little studied and promise additional insight into early solar system processes in both the solar nebula and on the Tagish Lake parent asteroid. We have examined an intact 2.9 g fragment and two polished thin sections from the spring 2000 (non-pristine) Tagish Lake collection to ascertain the major mineralogy and textures of notable features such as chondrules, amoeboid olivine aggregates (AOAs), inclusions, clasts, matrix, and fusion crust. We designed three stages of analysis for this friable meteorite: an initial, non-destructive in situ reconnaissance by μXRD to document meteorite mineralogy and textures and to identify features of interest, followed by spatially correlated μXRD, SEM-EDX and colour SEM-CL analysis of polished thin sections to fully understand mineralogy and the record of texture development, and finally higher resolution SEM-BSE mapping to document smaller scale relationships.Our analyses reveal several previously unreported or poorly characterized features: (1) distinctive colour cathodoluminescence (CL) zoning in relict CAI spinel, in chondrule and AOA forsterite, and in calcite nodules occurring throughout the Tagish Lake matrix. Forsterite frequently shows CL colour and intensity zonation that does not correspond with major or minor element differences resolvable with EPMA, indicating a trace element and/or structural CL-activation mechanism for the zonation that is likely of secondary origin; (2) an irregular inclusion dominated by magnesioaluminate spinel, dolomite, and phyllosilicates with traces of a Ca, Ti oxide phase (likely perovskite) interpreted to be a relict CAI; (3) variable preservation of mesostasis glass in porphyritic olivine chondrules. We anticipate that our multi-technique methodology, particularly non-destructive μXRD, can be successfully applied to other rare and friable materials such as the pristine Tagish Lake fragments.     

Fe‐bearing phases in a ureilite fragment from the asteroid 2008 TC3 (= Almahata Sitta meteorites): A combined Mössbauer spectroscopy and X‐ray diffraction study

The iron‐bearing phases in a ureilite fragment (AS#051) from the Almahata Sitta meteorite are studied using Mössbauer spectroscopy, X‐ray diffraction (XRD), and electron microprobe analysis (EMPA). AS#051 has a typical ureilite texture of medium‐ to coarse‐grained silicates (olivine, orthopyroxene, and pigeonite) with minor opaques (Fe‐Ni metal, troilite, and graphite). The silicate compositions, determined by EMPA, are homogeneous: olivine (Fo_90.2), orthopyroxene (En_86.3Fs_8.6Wo_5.1), and pigeonite (En_81.6Fs_8.9Wo_9.5), and are similar to those of magnesian ureilites. The modal abundance of mineral phases was determined by Rietveld refinement of the powder XRD data. The Mössbauer spectra at 295 K and 78 K are composed of two sharp well‐defined paramagnetic doublets superimposed on a well‐resolved magnetic sextet and other weak absorption features. The two paramagnetic doublets are assigned to olivine and pyroxene (orthopyroxene and pigeonite), and the ferromagnetic sextet to kamacite (magnetic hyperfine field ≈ 33.2 T), in agreement with the XRD characterization. The Mössbauer results also show the presence of small amounts of troilite (FeS) and cohenite ([Fe,Ni,Co]₃C). Using the Mössbauer data, the relative abundance of each Fe‐bearing phase is determined and compared with the results obtained by XRD.     

Light dement geochemistry of the Tagish Lake CI2 chondrite: Comparison with CI1 and CM2 meteorites

Abstract— We have studied the carbon and nitrogen stable isotope geochemistry of a small pristine sample of the Tagish Lake carbonaceous chondrite by high‐resolution stepped‐combustion mass spectrometry, and compared the results with data from the Orgueil (CI1), Elephant Moraine (EET) 83334 (CM1) and Murchison (CM2) chondrites. The small chip of Tagish Lake analysed herein had a higher carbon abundance (5.81 wt%) than any other chondrite, and a nitrogen content (?1220 ppm) between that of CI1 and CM2 chondrites. Owing to the heterogeneous nature of the meteorite, the measured carbon abundance might be artificially high: the carbon inventory and whole‐rock carbon isotopic composition (δ¹³C ? +24.4%_o) of the chip was dominated by ¹³C‐enriched carbon from the decomposition of carbonates (between 1.29 and 2.69 wt%; δ¹³C ? +67%_o and δ¹⁸O ? +35%_o, in the proportions ?4:1 dolomite to calcite). In addition to carbonates, Tagish Lake contains organic carbon (?2.6 wt%, δ¹³C ? ?9%_o; 1033 ppm N, δ¹⁵N ? +77%_o), a level intermediate between CI and CM chondrites. Around 2% of the organic material is thermally labile and solvent soluble. A further ?18% of the organic species are liberated by acid hydrolysis. Tagish Lake also contains a complement of presolar grains. It has a higher nanodiamond abundance (approximately 3650–4330 ppm) than other carbonaceous chondrites, along with ?8 ppm silicon carbide. Whilst carbon and nitrogen isotope geochemistry is not diagnostic, the data are consistent with classification of Tagish Lake as a CI2 chondrite.     

Molecular and isotopic analyses of Tagish Lake alkyl dicarboxylic acids

Abstract— The Tagish Lake meteorite soluble organic suite has a general composition that differs from those of both CI and CM chondrites. These differences suggest that distinct processes may have been involved in the formation of different groups of organics in meteorites. Tagish Lake alkyl dicarboxylic acids have a varied, abundant distribution and are, with carboxylated pyridines, the only compounds to have an occurrence comparable to that of the Murchison meteorite. This study has undertaken their molecular and isotopic characterization, with the aim to understand their origin and to gain insights into the evolutionary history of the meteorite parent body. Tagish Lake alkyl dicarboxylic acids are present as a homologous series of saturated and unsaturated species with three‐ through ten‐carbon atom chain length. Linear saturated acids are predominant and show decreasing amounts with increasing chain length. A total of 44 of these compounds were detected with the most abundant, succinic acid, present at ?40 nmol/g meteorite. Overall the molecular distribution of Tagish Lake dicarboxylic acids shows a remarkable compound‐to‐compound correspondence with those observed in the Murchison and Murray meteorites. In both Tagish Lake and Murchison, the imides of the more abundant dicarboxylic acids were also observed. The hydrogen and carbon isotopic compositions of individual Tagish Lake dicarboxylic acids were determined and compared to those of the corresponding acids in the Murchison meteorite. All δD and δ¹³C values for Tagish Lake acids are positive and show a substantial isotopic enrichment. δD values vary from, approximately, +1120%_o for succinic acid to +1530%_o for methyl glutaric acid. δ¹³C values ranged from +12.6%_o for methyl glutaric acid to +22.9%_o for glutaric acid, with adipic acid having a significantly lower value (+5.5%_o). Murchison dicarboxylic acid showed similar isotopic values: their δ5¹³C values were generally higher by an average 17% and δD values were lower for succinic and glutaric acids, possibly due to contamination. The molecular and isotopic data collected for these compounds restrict their possible origin to processes, either interstellar or of very cold nebular regions, that produced significant isotopic enrichments. Saturated or partially unsaturated nitriles and dinitriles appear to be good precursor candidates as their hydrolysis, upon water exposure, would produce dicarboxylic acids and other carboxylated species found in Tagish Lake. This evolutionary course could possibly include pre‐accretionary processes.     

The New Peruvian Meteorite Carancas: Mössbauer Spectroscopy and X-Ray Diffraction Studies

The Carancas meteorite fell on 15 September 2007 approximately 10 km south of Desaguadero, near Lake Titicaca, Peru, producing bright lights, clouds of dust in the sky and intense detonations. The Carancas meteorite is classified as a H4–5 ordinary chondrite with shock stage S3 and a degree of weathering W0. The Carancas meteorite is characterized by well defined chondrules composed either of olivine or pyroxene. The Mössbauer spectra show an overlapping of paramagnetic and magnetic phases. The spectra show two quadrupole doublets associated to olivine and pyroxene; and two magnetic sextets, associated with the primary phases kamacite/taenite and Troilite (Fe²⁺). Metal particles were extracted from the bulk powdered samples exhibit only kamacite and small amounts of the intergrowth tetrataenite/antitaenite. X-Ray diffractogram shows the primary phases olivine, pyroxene, troilite, kamacite, diopside and albite. Iron oxides has not been detected by Mössbauer spectroscopy or XRD as can be expected for a meteorite immediately recovered after its fall.     

Geochemistry of the ungrouped carbonaceous chondrite Tagish Lake,the anomalous CM chondrite Bells,and comparison with CI and CM chondrites

Abstract— I have determined the composition via instrumental neutron activation analysis of a bulk pristine sample of the Tagish Lake carbonaceous chondrite fall, along with bulk samples of the CI chondrite Orgueil and of several CM chondrites. Tagish Lake has a mean of refractory lithophile element/Cr ratios like those of CM chondrites, and distinctly higher than the CI chondrite mean. Tagish Lake exhibits abundances of the moderately volatile lithophile elements Na and K that are slightly higher than those of mean CM chondrites. Refractory through moderately volatile siderophile element abundances in Tagish Lake are like those of CM chondrites. Tagish Lake is distinct from CM chondrites in abundances of the most volatile elements. Mean CI‐normalized Se/Co, Zn/Co and Cs/Co for Tagish Lake are 0.68 ± 0.01, 0.71 ± 0.07 and 0.76 ± 0.02, while for all available CM chondrite determinations, these ratios lie between 0.31 and 0.61, between 0.32 and 0.58, and between 0.39 and 0.74, respectively. Considering petrography, and oxygen isotopic and elemental compositions, Tagish Lake is an ungrouped member of the carbonaceous chondrite clan. The overall abundance pattern is similar to those of CM chondrites, indicating that Tagish Lake and CMs experienced very similar nebular fractionations. Bells is a CM chondrite with unusual petrologic characteristics. Bells has a mean CI‐normalized refractory lithophile element/Cr ratio of 0.96, lower than for any other CM chondrite, but shows CI‐normalized moderately volatile lithophile element/Cr ratios within the ranges of other CM chondrites, except for Na which is low. Iridium, Co, Ni and Fe abundances are like those of CM chondrites, but the moderately volatile siderophile elements, Au, As and Sb, have abundances below the ranges for CM chondrites. Abundances of the moderately volatile elements Se and Zn of Bells are within the CM ranges. Bells is best classified as an anomalous CM chondrite.     

Glassy magnetic cronstedtite signatures in Mukundpura CM2 chondrite based on magnetic and Mössbauer studies

We have studied the Mukundpura CM2 meteorite for magnetic properties as a function of temperature and magnetic field, as well as its Mössbauer spectrum, at room and low temperatures (up to 5 K). We find that the high temperature paramagnetic phase is followed by two magnetic transitions: a weak transition near 125 K and a strong transition at 8 K. The weak (125 K) magnetic phase can be attributed to complex Fe²⁺–Fe³⁺ constituents present in the meteorite. The absence of the characteristic sextet corresponding to magnetite in Mossbauer spectrum indicates that this magnetic phase is not magnetite, which, if present, must be in insignificant amount. The 8 K magnetic ordering is superimposed with weak ferromagnetic ordering, showing spin‐glass transition. The Mössbauer spectrum taken at 5 K substantiates the observed spin‐glassy nature, as very large hyperfine field ~32 T is recorded, causing localized subordering leading to spin‐glass behavior. The Mössbauer spectra also confirm that iron is mainly present in serpentine‐group minerals, both in ferrous and ferric states. The complete serpentinization of basic silicates indicates aggressive hydrous alteration. These results show that the observed spin‐glass signature is a characteristic feature of the cronstedtite phase in CM meteorites. This feature is unique to carbonaceous CM chondrites and could be used for nondestructive, quick, and independent classification of this rare class of meteorites. Furthermore, the absence of olivine and the presence of cronstedtite in Mossbauer spectra show that the degree of aqueous alteration observed is the most severe in Mukundpura CM2 meteorite, as compared to many other CM2 meteorites. The degree of aqueous alteration in CM2 carbonaceous chondrites increases in the sequence: Paris, Murchison, Murray, Mighei, Nogoya, Cold Bokkeveld, and Mukundpura.     

Systematics of Mössbauer absorption areas in ordinary chondrites and applications to a newly fallen meteorite in Jodhpur,India

Abstract— Mössbauer absorption areas corresponding to ⁵⁷Fe in olivine, pyroxene, troilite, and the metallic phase in ordinary chondrites are shown to exhibit certain systematic behaviors. H chondrites occupy 2 distinct regions on the plot of metallic phase absorption area versus silicate absorption area, while L/LL chondrites fall in a separate region. Similar separation is also observed when pyroxene absorption area is plotted against olivine absorption area. The one‐dimensional plot for the ratio of olivine area to pyroxene area separates L and LL chondrites. Based on these systematics, a newly fallen meteorite at Jodhpur, India is suggested to be an LL chondrite.     

Characterization of the matrix and fusion crust of the recent meteorite fall Ozerki L6

We studied the interior and the fusion crust of the recently recovered Ozerki L6 meteorite using optical microscopy, scanning electron microscopy (SEM) with energy dispersive spectroscopy, X‐ray diffraction (XRD), magnetization measurements, and Mössbauer spectroscopy. The phase composition of the interior and of the fusion crust was determined by means of SEM, XRD, and Mössbauer spectroscopy. The unit cell parameters for silicate crystals were evaluated from the X‐ray diffractograms and were found the same for the interior and the fusion crust. Magnetization measurements revealed a decrease of the saturation magnetic moment in the fusion crust due to a decrease of Fe‐Ni‐Co alloy content. Both XRD and Mössbauer spectroscopy show the presence of magnesioferrite in the fusion crust. The temperatures of cation equilibrium distribution between the M1 and M2 sites in silicates calculated using the data obtained from XRD and Mössbauer spectroscopy appeared to be in a good consistency: 553 and 479 K for olivine and 1213 and 1202 K for orthopyroxene.     

Application of Mössbauer spectroscopy,multidimensional discriminant analysis,and Mahalanobis distance for classification of equilibrated ordinary chondrites

Mössbauer spectra of equilibrated ordinary chondrites consist of two doublets due to paramagnetic iron present in olivines and pyroxenes and two sextets due to magnetically ordered iron present in metallic phases and troilite. The spectral areas of the different mineralogical phases found by Mössbauer spectroscopy in meteorites are proportional to the number of iron atoms in this mineralogical phase. This property of Mössbauer spectra can be the basis for constructing a method for the classification of ordinary chondrites. This idea was first explored at the Mössbauer Laboratory in Kanpur. This group suggested a qualitative method based on 2‐dimensional plots of Mössbauer spectral areas and thus classified properly some meteorites. We constructed a quantitative method using Mössbauer spectral areas, multidimensional discriminant analysis, and Mahalanobis distance (4M method) to determine the probability of a meteorite to be of type H, L, or LL. Based on 59 Mössbauer spectra, we calculated by the 4M method, S _cluster , the level of similarity of the Goronyo meteorite to the clusters. On the plot of ferrosilite versus fayalite, the point representing Goronyo is located on the border between H and L areas. Calculated by the 4M method, the meteorite Goronyo is 32% similar to type H, 75% to type L, and 11% to type LL. Additional mineralogical analyses suggested that the Goronyo meteorite would be classified as type L, although it was originally reported as type H in the Meteoritical Bulletin Database.     

A study of ordinary chondrites by Mössbauer spectroscopy with high‐velocity resolution

Abstract— An improvement in the velocity resolution and quality of Mössbauer spectra has been applied to a group of ordinary chondrites. This improvement permitted us to carry out a more detailed study of the iron bearing phases in these samples than has previously been possible. Mössbauer spectra of 11 ordinary chondrites of L and H chemical groups were measured using 4096 channels and presented for further analysis in 1024 channels. Subspectra of the metal grains of several chondrites demonstrated the presence of at least two magnetic sextets related to the main Fe(Ni, Co) phases. Moreover, Mössbauer study of extracted metal grains from Tsarev L5 revealed three sextets and one singlet spectral components related to various α‐Fe(Ni, Co), α‘‐Fe(Ni, Co), α₂‐Fe(Ni, Co), and γ‐Fe(Ni, Co) phases. Each subspectrum of olivine and pyroxene in Mössbauer spectra of ordinary chondrites was fitted by superposition of two quadrupole doublets related to M1 and M2 sites in minerals for the first time. An analysis of relative areas and Mössbauer hyperfine parameters was performed and some differences for L and H chondrites as well as for M1 and M2 sites were observed. Mössbauer parameters of troilite and oxidized iron were analyzed. In contrast to a previous study with 512‐channel spectra, the presence of oxidized iron was found in all chondrites.     

The oxygen isotopic composition of water from Tagish Lake: Its relationship to low‐temperature phases and to other carbonaceous chondrites

Abstract— The fall and recovery of the Tagish Lake meteorite in British Columbia in January 2000 provided a unique opportunity to study relatively pristine samples of carbonaceous chondrite material. Measurements of the oxygen isotopic composition of water extracted under stepped pyrolysis from a bulk sample of this meteorite have allowed us to make comparisons with similar data obtained from CI and CM chondrites and so further investigate any relationships that may exist between these meteorites. The much lower yield of water bearing a terrestrial signature in Tagish Lake is indicative of the pristine nature of the meteorite. The relationship between the isotopic composition of this water and reported isotopic values for carbonates, bulk matrix and whole rock have been used to infer the extent and conditions under which parent‐body aqueous alteration occurred. In Tagish Lake the difference in Δ17O isotopic composition between the water and other phases is greater than that found in either CM or CI chondrites suggesting that reaction and isotopic exchange between components was more limited. This in turn suggests that in the case of Tagish Lake conditions during the processes of aqueous alteration on the parent body, which ultimately controlled the formation of new minerals, were distinct from those on both CI and CM parent bodies.