THE MAGNETIC INVESTIGATION OF THE SIKHOTE-ALIN IRON METEORITE SHOWER AT THE SITE OF FALL

Individual and splinter specimens of the iron meteorite shower of Sikhote-Alin and rock samples from impact craters have been studied magnetically. The results indicate that: 1) Histograms for the distribution of natural remanent magnetization J_n of individual and splinter specimens are characterized by a high correlation coefficient (0.82 ± 0.06). For the splinter specimens, a trend to an increase in number of specimens with anomalously high J_n values is observed; 2) the Earth's magnetic field did not greatly affect the magnetic properties of this iron meteorite; and 3) for rock samples taken from different craters, there was found to be a relation between the natural remanent magnetization and the energy conditions of the crater formation.     

THE KRAMER CREEK,COLORADO METEORITE: A NEW L4 CHONDRITE

The Kramer Creek, Colorado, chondrite was found in 1966 and identified as a meteorite in 1972. Bulk chemical analysis, particularly the total iron content (20.36%) and the ratio of Fe_total/SiO₂ (0.52), as well as the compositions of olivine (Fa_21.7) and orthopyroxene (Fs_18.3) place the meteorite into the L-group of chondrites. The well-defined chondritic texture of the meteorite, the presence of igneous glass in the chondrules and of low-Ca clinopyroxene, as well as the slight variations in FeO contents of olivine (2.4% MD) and orthopyroxene (5.6% MD) indicate that the chondrite belongs to the type 4 petrologic class.     

New insights into the mineralogy and weathering of the Meridiani Planum meteorite,Mars

Meridiani Planum is the first officially recognized meteorite find on the surface of Mars. It was discovered at and named after the landing site of the Mars Exploration Rover Opportunity. Based on its composition, it was classified as a IAB complex iron meteorite. Mössbauer spectra obtained by Opportunity are dominated by kamacite (α‐Fe‐Ni) and exhibit a small contribution of ferric oxide. Several small features in the spectra have been neglected to date. To shed more light on these features, five iron meteorite specimens were investigated as analogs to Meridiani Planum with a laboratory Mössbauer setup. Measurements were performed on (1) their metallic bulk, (2) troilite (FeS) inclusions, (3) cohenite ((Fe,Ni,Co)₃C) and schreibersite ((Fe,Ni)₃P), and (4) corroded rims. In addition to these room‐temperature measurements, a specimen from the Mundrabilla IAB‐ungrouped meteorite was measured at Mars‐equivalent temperatures. Based on these measurements, the features in Meridiani Planum spectra can be explained with the presence of small amounts of schreibersite and/or cohenite and iron oxides. The iron oxides can be attributed to a previously reported coating on Meridiani Planum. Their presence indicates weathering through the interaction of the meteorite with small amounts of water.     

The mineralogy of the Yaringie Hill meteorite—A new H5 chondrite from South Australia

Abstract— The Yaringie Hill meteorite is a new H5 ordinary chondrite found in the Gawler Ranges, South Australia. The meteorite, which shows only minor signs of terrestrial weathering, is predominantly composed of olivine (Fa_17.2), orthopyroxene (Fs_15.1Wo_1.1), and three distinct phases of nickeliferous iron metal (kamacite, taenite, tetrataenite). Other minerals include troilite, plagioclase (Ab₈₁An₁₆Or₃), clinopyroxene (En₅₂Wo₄₂Fs₆), chlorapatite, merrillite, ilmenite, and native copper. Three types of spinel with distinctive textures (coarse, skeletal aggregates, rounded aggregates) and with compositions close to the join MgAl₂O₄‐FeCr₂O₄ are also present. Chondrules within the Yaringie Hill meteorite, which often have poorly defined boundaries, are placed in a recrystallized matrix. Shock indicators suggest that the meteorite experienced only weak shock metamorphism (S3).     

FORMS OF NONTERRESTRIAL DUST ON THE EARTH

The author carried out a study of pulverised cosmic matter extracted from the soil at the fall locality of the Sikhote Alin iron meteorite shower. Three forms of dust were distinguishable: meteoritic, sharp-angled, irregular particles from the break-up of the meteorite; meteoric, spherical, magnetic particles from ablation; and micro meteorites. Meteoritic and meteoric dust was also discovered in the soil of the regions of fall of the Boguslavka and Yardymly iron meteorites. Experiments made by the author for the purpose of obtaining artificial meteoric dust from meteoritic matter of various types have shown that the meteoric dust obtained from stony meteorites is composed of spherules similar to those extracted from the soil in the areas of fall of the Sikhote Alin, Boguslavka and Yardymly iron meteorites. Cosmic dust, the particles of which are usually called micrometeorites, due to their small size, are not subjected to the influence of temperature as they pass through the Earth's atmosphere and they reach the Earth's surface unaltered. It is proposed that meteoric and cosmic dust comprises the largest part of the cosmic matter falling onto the Earth:     

Oral histories in meteoritics and planetary science—XXV: Vagn F. Buchwald

Vagn Buchwald (Fig.  1 ) was born in Copenhagen where he attended school and college. Then after 18 months of military service, he assumed a position at the Technical University of Copenhagen. A few years later, he was presented with a piece of the Cape York meteorite, which led to an interest in iron meteorites. Through a campaign of informed searching, Vagn found the 20 ton Agpalilik meteorite (part of the Cape York shower) on 31st July 1963 and by September 1967 had arranged its transport to Copenhagen. After sorting and describing the Danish collection, which included application of the Fe‐Ni‐P phase diagram to iron meteorite mineralogy, Vagn was invited to sort and describe other iron meteorite collections. This led to a 7 yr project to write his monumental Handbook of Iron Meteorites. Vagn spent 3 yr in the United States and visited most of the world's museums, the visit to Berlin being especially important since the war had left their iron meteorites in bad condition and without labels. During a further decade or more of iron meteorite research, he documented natural and anthropomorphic alterations experienced by iron meteorites, discovered five new minerals (roaldite, carlsbergite, akaganeite, hibbingite, and arupite); had a mineral (buchwaldite, NaCaPO₄) and asteroid (3209 Buchwald 1982 BL1) named after him; and led expeditions to Chile, Namibia, and South Africa in search of iron meteorites and information on them. Vagn then turned his attention to archeological metal artifacts. This work resulted in many papers and culminated in two major books on the subject published in 2005 and 2008, after his retirement in 1998. Vagn Buchwald has received numerous Scandinavian awards and honors, and served as president of the Meteoritical Society in 1981–1982.     

THE NORTON COUNTY METEOROID: A CASE FOR STATISTICAL STUDY OF METEORITE FRAGMENTS

The size distribution of 15,000 fragments from the Norton County meteorite was examined with size-frequency histogram. The size is measured in phi units. The estimates of the moments β₁ and β₂ of the empirical distribution were used for approximating the latter with a theoretical frequency curve in terms of the Pearson system It was suggested that the beta distribution obtained from the Pearson system can be regarded as a superposition of two simpler distributions: a near to normal one, corresponding to a slower process of fragmentation, and a power-law one, assumed to result from fast fragmentation process. … All meteorite falls are important but some are more important than others … … This fall was of outstanding importance because with its arrival the entire picture of the word meteorite as portrayed in the total of collections throughout the world was notably altered … H. H. Nininger, 1949. Significance of the Norton, Kansas, meteorite in Transactions of the Kansas Academy of Sciences 52 , 113.     

THE CHEMISTRY AND MINERALOGY OF THE HOMEWOOD,MANITOBA, METEORITE

The Homewood meteorite is a slightly weathered find of 325 grams discovered in 1970 about 64 km southwest of Winnipeg, Manitoba. It consists of olivine (Fa_25.4; 43.8 normative wt. percent), orthopyroxene (Fs_23.3; 28.5 percent), kamacite and taenite (7.5 percent), troilite (5.6 percent), maskelynite (8.3 percent), chromite (1.0 percent), whitlockite (0.7 percent) and minor patchy Ca pyroxene. Bulk chemical analysis yielded Fe_total 21.60 wt. percent, Fe/SiO₂0.55, SiO₂/MgO 1.53 and Fe^O/Fe_total 0.29. Barred olivine, radiating pyroxene and porphyritic chondrules, all with ill-defined outlines, occur in the meteorite. Most chemical and mineralogical features characterize the Homewood meteorite as an L6 (hypersthene) chondrite. The presence of maskelynite, the undulatory extinction, extensive fracturing and pervasive mosaicism of olivine, and the poor definition of chondrule outlines suggest that the Homewood meteorite has been shocked in the range of 300–350 kbar.     

Evolution of molten material in iron cores of small planets

A parent body of the Lovina meteorite underwent processes which yielded dentritic structures of taenite in phosphide-sulfide-metal matrix unusual for iron meteorites. Similar dendritic structures can be found also in IIE meteorites as microinclusions but are unknown in other iron meteorites. The similarity between dendritic structures in the Lovina meteorite and metal-phosphide inclusions in IIE iron meteorites implies similar processes which led to their crystallization from molten materials in chambers of various sizes. Studying physical and chemical crystallization parameters of metal-phosphide inclusions in the Elga meteorite (IIE) makes it feasible to estimate the p-T conditions required for the unique Lovina meteorite to have formed. It is shown that dendrites in the Lovina meteorite may have been crystallized from molten materials close in composition to P-FeNi and P-S-FeNi that are produced when phosphides and sulfides melt locally in metals as a result of impact events with subsequent fast cooling. The temperature of homogeneous melting is likely to have been more than 1450°C, and the starting temperature of crystallization of such molten materials is estimated to have been between 1050 and 1150°C. The cooling rate of inclusions can be estimated to be 10⁻³ °C s⁻¹, based on the structural and chemical concordance between samples obtained experimentally (Chabot et al., 2000) and metal-phosphide inclusions (P-FeNi and P-S-FeNi) in the Elga meteorite. Large-sized dendrites in the Lovina meteorite imply cooling rates that are considerably less than 10⁻³ °C s⁻¹.     

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.     

Rumanová H5 chondrite,Slovaki

Abstract— An H5 chondrite was found near the village of Rumanová, Slovakia. dominant minerals of the meteorite are enstatite, olivine, kamacite, taenite and troilite. The minor minerals are oligoclase, augite, pigeonite, accessory chromite, whitlockite and chlorapatite. The composition of olivine (Fa_19.0) and low-Ca orthopyroxene (Fs_17.0), and the density and chemical composition of the meteorite correspond to those of an H chondrite. Normal zoning of Ni in metal grains and parallel planar fractures in olivine suggest weak shock metamorphism of stage S3. Due to moderate oxidation of metal, iron hydroxides were formed corresponding to weathering stage W2.     

THE BLOOMINGTON (LL6) CHONDRITE AND ITS SHOCK MELT GLASSES

The Bloomington meteorite, a 67.8 gram veined, brecciated chondrite, fell during the summer of 1938 in Bloomington, Illinois. Its olivine, orthopyroxene and metal compositions (fo₆₉, en₇₄ and Fe₅₂ Ni₄₈ respectively) and its texture identify it as a brecciated LL6 chondrite of shock facies d. Shock melt glasses occur in Bloomington as sparse melt pockets and veins in clasts and as isolated masses in the black, clast-rich matrix. The vein glasses chemically resemble bulk LL-group chondrites and thus appear to reflect total melting of the host meteorite. The melt pocket and matrix glasses, like those described previously in L-group chondrites, have more varied compositions and are typically enriched in normative plagioclase. All glasses that we analyzed in Bloomington have FeO/MgO and Na/Al ratios similar to those of LL-group chondrites, indicating that melting of this meteorite involved neither a significant change in the oxidation state of iron nor loss of sodium to a vapor phase. Bloomington is a monomict breccia whose components formed in place as a result of a single episode of shock and attendant melting.     

53Mn and 60Fe in iron meteorites—New data,model calculations

We measured specific activities of the long‐lived cosmogenic radionuclides ⁶⁰Fe in 28 iron meteorites and ⁵³Mn in 41 iron meteorites. Accelerator mass spectrometry was applied at the 14 MV Heavy Ion Accelerator Facility at ANU Canberra for all samples except for two which were measured at the Maier‐Leibnitz Laboratory, Munich. For the large iron meteorite Twannberg (IIG), we measured six samples for ⁵³Mn. This work doubles the number of existing individual ⁶⁰Fe data and quadruples the number of iron meteorites studied for ⁶⁰Fe. We also significantly extended the entire ⁵³Mn database for iron meteorites. The ⁵³Mn data for the iron meteorite Twannberg vary by more than a factor of 30, indicating a significant shielding dependency. In addition, we performed new model calculations for the production of ⁶⁰Fe and ⁵³Mn in iron meteorites. While the new model is based on the same particle spectra as the earlier model, we no longer use experimental cross sections but instead use cross sections that were calculated using the latest version of the nuclear model code INCL. The new model predictions differ substantially from results obtained with the previous model. Predictions for the ⁶⁰Fe activity concentrations are about a factor of 2 higher, for ⁵³Mn, they are ~30% lower, compared to the earlier model, which gives now a better agreement with the experimental data.     

Ultra‐reduced phases in Apollo 16 regolith: Combined field emission electron probe microanalysis and atom probe tomography of submicron Fe‐Si grains in Apollo 16 sample 61500

The lunar regolith contains a variety of chemically reduced phases of interest to planetary scientists and the most common, metallic iron, is generally ascribed to space weathering processes (Lucey et al. 2006 ). Reports of silicon metal and iron silicides, phases indicative of extremely reducing conditions, in lunar samples are rare (Anand et al. 2004 ; Spicuzza et al. 2011 ). Additional examples of Fe‐silicides have been identified in a survey of particles from Apollo 16 sample 61501,22. Herein is demonstrated the utility of low keV electron probe microanalysis (EPMA), using the Fe Ll X‐ray line, to analyze these submicron phases, and the necessity of accounting for carbon contamination. We document four Fe‐Si and Si⁰ minerals in lunar regolith return material. The new Fe‐Si samples have a composition close to (Fe,Ni)₃Si, whereas those associated with Si⁰ are close to FeSi₂ and Fe₃Si₇. Atom probe tomography of (Fe,Ni)₃Si shows trace levels of C (60 ppma and nanodomains enriched in C, Ni, P, Cr, and Sr). These reduced minerals require orders of magnitude lower oxygen fugacity and more reducing conditions than required to form Fe⁰. Documenting the similarities and differences in these samples is important to constrain their formation processes. These phases potentially formed at high temperatures resulting from a meteorite impact. Whether carbon played a role in achieving the lower oxygen fugacities—and there is evidence of nearby carbonaceous chondritic material—it remains to be proven that carbon was the necessary component for the unique existence of these Si⁰ and iron silicide minerals.     

Weathering in Antarctic H and CR chondrites: Quantitative analysis through Mössbauer spectroscopy

Abstract— Mössbauer spectroscopy is a very useful tool for identifying ferric iron weathering products in meteorites because of the capability to quantify the relative amounts of ferric iron in them. Mössbauer measurements were made of 33 Antarctic H chondrites (predominately H5) and two paired Antarctic CR chondrites. The primary goals of this study are to determine if Mössbauer spectroscopy can be used to determine which phases are weathering in Antarctic meteorites and if the relative amounts of ferric iron correlate with terrestrial age. Determining which minerals are weathering in ordinary chondrites appears very difficult due to variations in composition for different ordinary chondrites of the same meteorite class and possible problems in preparing homogeneous samples. The analysis of the two paired CR chondrites appears to indicate that metallic iron is predominately weathering to produce ferric iron for this class of meteorite. No correlation is seen between the relative amounts of ferric iron and terrestrial age for ordinary chondrites. One Antarctic H5 chondrite (ALHA77294) with a short ¹⁴C age of 135 ± 200 years from the dating of interior carbonate weathering products does have a relatively low amount of ferric iron, which is consistent with this meteorite being exposed on the surface for a relatively short time.     

THE COMPOSITION OF THE JOHNSTOWN METEORITE

A new analysis of the Johnstown meteorite, a hypersthene achondrite, gives the following results (weight percent): SiO₂ 53.48, TiO₂ 0.12, Al₂O₃ 1.43, Cr₂O₃ 0.83, FeO 15.63, MnO 0.54, MgO 25.87, CaO 1.40, Na₂O 0.04, K₂O 0.00, P₂O₅ 0.00, H₂O+ <0.1, H₂O- 0.05, Ni <0.05, Co <0.01, FeS 1.18, sum 100.57. Published and unpublished data on minor and trace elements in the bulk meteorite and in the pyroxene are presented in tabular form.     

A gamma‐ray spectroscopy survey of Omani meteorites

The gamma‐ray activities of 33 meteorite samples (30 ordinary chondrites, 1 Mars meteorite, 1 iron, 1 howardite) collected during Omani‐Swiss meteorite search campaigns 2001–2008 were nondestructively measured using an ultralow background gamma‐ray detector. The results provide several types of information: Potassium and thorium concentrations were found to range within typical values for the meteorite types. Similar mean ²⁶Al activities in groups of ordinary chondrites with (1) weathering degrees W0‐1 and low ¹⁴C terrestrial age and (2) weathering degree W3‐4 and high ¹⁴C terrestrial age are mostly consistent with activities observed in recent falls. The older group shows no significant depletion in ²⁶Al. Among the least weathered samples, one meteorite (SaU 424) was found to contain detectable ²²Na identifying it as a recent fall close to the year 2000. Based on an estimate of the surface area searched, the corresponding fall rate is ~120 events/10⁶ km²*a, consistent with other estimations. Twelve samples from the large JaH 091 strewn field (total mass ~4.5 t) show significant variations of ²⁶Al activities, including the highest values measured, consistent with a meteoroid radius of ~115 cm. Activities of ²³⁸U daughter elements demonstrate terrestrial contamination with ²²⁶Ra and possible loss of ²²²Rn. Recent contamination with small amounts of ¹³⁷Cs is ubiquitous. We conclude that gamma‐ray spectroscopy of a selection of meteorites with low degrees of weathering is particularly useful to detect recent falls among meteorites collected in hot deserts.     

Lunar meteorites from Oman

Abstract– Sixty named lunar meteorite stones representing about 24 falls have been found in Oman. In an area of 10.7 × 10³ km² in southern Oman, lunar meteorite areal densities average 1 g km^?2. All lunar meteorites from Oman are breccias, although two are dominated by large igneous clasts (a mare basalt and a crystalline impact‐melt breccia). Among the meteorites, the range of compositions is large: 9–32% Al₂O₃, 2.5–21.1% FeO, 0.3–38 μg g^?1 Sm, and <1 to 22.5 ng g^?1 Ir. The proportion of nonmare lunar meteorites is higher among those from Oman than those from Antarctica or Africa. Omani lunar meteorites extend the compositional range of lunar rocks as known from the Apollo collection and from lunar meteorites from other continents. Some of the feldspathic meteorites are highly magnesian (high MgO/[MgO + FeO]) compared with most similarly feldspathic Apollo rocks. Two have greater concentrations of incompatible trace elements than all but a few Apollo samples. A few have moderately high abundances of siderophile elements from impacts of iron meteorites on the Moon. All lunar meteorites from Oman are contaminated, to various degrees, with terrestrial Na, K, P, Zn, As, Se, Br, Sr, Sb, Ba, U, carbonates, or sulfates. The contamination is not so great, however, that it seriously compromises the scientific usefulness of the meteorites as samples from randomly distributed locations on the Moon.     

THE MINERALOGY AND CHEMISTRY OF THE ALTA'AMEEM METEORITE

The Alta'ameem hypersthene chondrite is a light gray brecciated and metamorphosed meteorite composed mainly of olivine (27% Fa), orthopyroxene (24.5% Fs) and plagioclase (An¹⁰). Other minerals include troilite, kamacite, taenite, chromite, ilmenite, clinopyroxene, chalcopyrite, and apatite or merrillite. The mineralogical and chemical analyses suggest that the Alta'ameem meteorite belongs to the amphoterite group of chondrites. The chemical composition includes the following: Fe 3.39, Ni 1.13, Co 0.05, Cu 0.01, FeS 6.48, SiO₂ 39.48, TiO₂ 0.28, Al₂O₃ 2.25, FeO 16.46, MnO 0.40, MgO 25.66, CaO 1.47, Na₂O 1.05, K₂O 0.15, P₂O₅ 0.47, Cr₂O₃ 0.45; total 99.18.     

The abundance and isotopic composition of Cd in iron meteorites

Cadmium is a highly volatile element and its abundance in meteorites may help better understand volatility‐controlled processes in the solar nebula and on meteorite parent bodies. The large thermal neutron capture cross section of ¹¹³Cd suggests that Cd isotopes might be well suited to quantify neutron fluences in extraterrestrial materials. The aims of this study were (1) to evaluate the range and magnitude of Cd concentrations in magmatic iron meteorites, and (2) to assess the potential of Cd isotopes as a neutron dosimeter for iron meteorites. Our new Cd concentration data determined by isotope dilution demonstrate that Cd concentrations in iron meteorites are significantly lower than in some previous studies. In contrast to large systematic variations in the concentration of moderately volatile elements like Ga and Ge, there is neither systematic variation in Cd concentration amongst troilites, nor amongst metal phases of different iron meteorite groups. Instead, Cd is strongly depleted in all iron meteorite groups, implying that the parent bodies accreted well above the condensation temperature of Cd (i.e., ≈650 K) and thus incorporated only minimal amounts of highly volatile elements. No Cd isotope anomalies were found, whereas Pt and W isotope anomalies for the same iron meteorite samples indicate a significant fluence of epithermal and higher energetic neutrons. This observation demonstrates that owing to the high Fe concentrations in iron meteorites, neutron capture mainly occurs at epithermal and higher energies. The combined Cd‐Pt‐W isotope results from this study thus demonstrate that the relative magnitude of neutron capture‐induced isotope anomalies is strongly affected by the chemical composition of the irradiated material. The resulting low fluence of thermal neutrons in iron meteorites and their very low Cd concentrations make Cd isotopes unsuitable as a neutron dosimeter for iron meteorites.