Meteorite Specimens Research Articles

The Meteoritical Bulletin, No. 76, 1994 January: The U.S. Antarctic Meteorite Collection*

Abstract— The Meteoritical Bulletin number 76 contains a list of all classified meteorites collected by the United States' Antarctic meteorite program as of the summer of 1993. The compilation includes available information on classification, mass, weathering, olivine and pyroxene composition, 26Al activities, natural thermoluminescence levels, pairing, collection location and references to published descriptions for 5537 meteorite specimens. A list of the properties of metallic meteorites and a list of the most significant meteorites by class are also included.

Variations of the isotopic composition of sulfur in enstatite and ordinary chondrites

High-precision sulfur isotopic analyses (δ 33S, δ 34S, and δ 36S) of bulk ordinary and enstatite chondrites demonstrate that systematic variations exist. The average δ 34S values are −0.26 ± 0.07, −0.02 ± 0.06, and 0.49 ± 0.16%. for enstatite and ordinary and carbonaceous chondrites, respectively. Isotopic variations of different sample specimens of primitive meteorites, e.g., Qingzhen and Abee, have been observed which may be attributed to heterogeneity in the early solar nebula. Sulfur isotopic fractionations in both bulk samples and mineral separates are mass-dependent, and no nuclear isotopic anomalies have been detected. The sulfur isotopic compositions of both mineral and density separates have been measured. The sulfur isotopic compositions of separated chondrules from Chainpur and Bjurbole are reported. Significant isotopic difference for the chondrules from the bulk meteorite are noted for both meteorites.

The behavior of Fe-Ni metal during thermal metamorphism of the Jilin Chondrite

1. Under heat influence, the mobility of Fe-Ni metal was relatively high as compared with silicates. During thermal metamorphism of the Jilin meteorite (T ⩽ 800 °C), fine Fe-Ni metal particles in silicate condrules and matrix aggregated into coarse metal grains, which are as large as 5–10 mm in size,in situ or after a short-distance migration and concentration, and some even aggregated into metal nodules as large as 20–30mm in size, but their chemical composition still remains unchanged. 2. High-temperature and high pressure, as well as shock-loading experiments on Jilin meteorite samples provide further evidence that temperature plays an important role in metal /silicate redistribution and differentiation. The variation of temperature exerts great influence on the mode of metal-silicate redistribution. At about 1000 °C or less, metal particles moved and aggregated into rather coarse grains by thermal diffusion, or through the formation of eutectic melts together with FeS. When the temperature reaches about 1300 °C, full melting take place in the meteorite specimens, and at this time metals and metal sulfides play an important role in the immiscibility and gravitational differentiation of metal-silicate melts, thus leading to the rapid separation of metals or metal-sulfides from silicates, followed by the sinking of pure metals and metal-sulfides to the bottom of the experimental products and the formation of silicate melts almostly with no metals and sulfides in the upper parts.

The Dependence of Thermoluminescence Sensitivity Upon the Temperature of Irradiation in Meteorites and in Terrestrial Apatites

Abstract Measurements are reported on the TL sensitivity (i.e. TL glow output per unit ? ray test dose) of meteoritic specimens as well as terrestrial fluor- and chlor-apatites, as a function of irradiation temperature (Tirr). The irradiation temperatures ranged from liquid nitrogen to room temperature (77 - 293 K). A kilocurie 60Co ? ray source was used to deliver test doses of 400 Gy (40 krad) and 40 Gy (4 krad) to the various samples. A strong dependence of the TL sensitivity upon the temperature of irradiation was noted in the case of Kirin meteorite: its TL sensitivity (for the 493 K readout peak) decreased by a factor of ~2 when Tirr rose from liquid nitrogen (77 K) to dry ice in acetone (197 K) temperature, in the case of both 400 Gy and 40 Gy ? ray doses. In the case of the Antarctic meteorite specimen (ALHA 77182,13), there was a smaller effect, viz. a fall of ~14% in the TL output corresponding to dry ice and higher irradiating temperatures as compared to the 77 K irradiation. For chlorapatite, the TL sensitivity decreased monotonically with increasing temperature for both the 563 K and the 448 K glow peaks. For the fluorapatite, the effect of reduced response was observed only between -17 oC (256 K) and room temperature (293 K). Both the theoretical and the practical implications of these observations are discussed.

Helium, neon, and argon in meteorites—A data compilation

Noble gases have been measured in meteorites for more than 100 years. The last 50 years have been especially fruitful, with concentration and isotopic compositional analysis of He, Ne, Ar, Kr, and Xe making important contributions to meteorite research. Differently trapped noble gas components are the basis for understanding planetary atmospheres and even different stages of stellar evolution. Noble gases are a valuable tool to detect pairing of meteorite specimens or even to prove whether a rock is a meteorite or not. Noble gas data, however, are distributed over a large number of publications. Sometimes, only concentrations are given for selected isotopes or just a simple derivative quantity is published. We have tried to collect all available measurements of He, Ne, and Ar in meteorites. Here, we present the data in a form that will help easily calculate isotopic or elemental ratios for selected measurements. The present compilation contains all data available as of March 2004.

Geochemical investigations to explain iodine-overabundances in Antarctic meteorites

Iodine, bromine, and chlorine concentrations were determined in different Antarctic meteorite specimens (eucrites, high-iron and low-iron chondrites) with isotope dilution mass spectrometry. In all Antarctic meteorites I-overabundances have been analysed compared with the concentrations for non-Antarctic meteorites of the same class. Half of the Antarctic specimens show especially high concentrations of more than 1 μ/g. A similarly high enrichment effect in Antarctic meteorites was not found for Br and Cl, but smaller Cl excesses could be observed in some eucrites and high-iron chondrites. By analysing different types of Antarctic rocks, a significant decrease of the I concentration—but not of the Br and Cl concentration-was determined from the surfaces to the centers of the rocks. This shows that atmospheric I compounds interact with the surfaces of Antarctic rocks and, therefore, with those of Antarctic meteorites as well. Analyses of atmospheric halogens show that the gaseous compound CH 3I is probably responsible for the I-overabundance in Antarctic meteorites and rocks. Chloride and bromide are found in particles derived from sea-spray in Antarctic aerosols. Deposition of halogens in Antarctic snow near the coast shows I/Cl ratios 10–190 higher than the average value for seawater. The corresponding Br/Cl ratios are in the same range as seawater. On the basis of our results and of other reported data we construct a preliminary hypothesis for a geochemical I cycle in Antarctica, taking into consideration long-distance and short-distance transportation of different I compounds from the coast to inland Antarctica.

Photographic Catalog of the Selected Antarctic Meteorites

The collection of new meteorite specimens from Antarctica has commanded the attention of interested scientists for the past decade. Meteorites have been collected in large numbers by Japanese exploration teams in the Yamato Mountains, East Antarctica region. The first meteorites were discovered there in 1969. Expeditions in 1973, 1974, 1975–1976, and 1979–1980 have added over 4000 meteorites to the National Institute of Polar Research Collection. Another 700 were added in 1976 through 1979 by joint Japan‐United States teams in the Transantarctic Mountains, South Victoria Land. It should be noted that when meteoroids fall, they usually break up into many pieces. It has not been established how many individual falls make up this large collection of individuals. The Photographic Catalog of the Selected Antarctic Meteorites contains 178 photographs of 134 meteorites selected from the NIPR Collection. The majority of the photographs are of whole or broken stones in the condition they were found on the ice. Some photographs show cut or broken faces made during the sampling of the meteorites for investigation. A brief description of the specimen is included with each photograph. The publishers hope that these photographs and hand‐specimen descriptions will be helpful in guiding detailed petrologic, chemical, and physical studies in the future.

CANADIAN ARCTIC METEORITE SEARCH: 1981

The recovery of several thousand meteorite fragments from Antarctica has led to speculation that accumulations may occur on the Earth's other major ice caps. Meteorites falling over the past 80,000 years on the Devon Island ice cap in the Canadian Arctic may be exposed at the surface near the ice cap margin. From the terrestrial meteorite flux, ice movement rates, and fragmentation factors it is calculated that 12,560 samples of 150 g mass are potentially concentrated in a 65 km2 zone along the northwest margin. A search of this region on foot and by helicopter in July, 1981, failed to recover any specimens. Although metre‐sized gneissic boulders, plucked from the underlying Precambrian basement, were concentrated in this zone it is postulated that the unseasonal 30 cm snow cover on the ice prohibited the recognition of possible meteorite specimens, which may average only 5 cm in diameter.

THE DERRICK PEAK, ANTARCTICA, IRON METEORITES

Sixteen iron meteorite specimens, Derrick Peak A78001 through DRPA78016, were recovered from the slopes of Derrick Peak, Antarctica, in 1978. Recovery from a relatively small area combined with their strikingly similar appearances suggest they represent a single fall. The metallographic structure of the two specimens that have been cut is dominated by regions of swathing kamacite enclosing coarse schreibersite and schreibersite‐troilite inclusions. Patches of coarsest octahedrite Widmanstätten structure are interspersed. Specimens DRPA78008 and DRPA78009 have been analyzed: 6.64, 6.59 wt % Ni; 0.51, 0.46 wt % Co; 0.35, 0.34 wt % P. The specimens are coarsest octahedrites of chemical group IIB.

An Antarctic iron meteorite contains preterrestrial impact-produced diamond and lonsdaleite

Of the many meteorites recovered so far from the Allan Hills, Antarctica, only nine have been irons. One of these, ALHA77283, contains troilite(FeS)–graphite(C)–schreibersite((Fe,Ni)3P)–cohenite(Fe3C) inclusions rich in the carbonado-type diamond–lonsdaleite ‘nodules’ previously described from the Canyon Diablo meteorite1,2. The Canyon Diablo, Arizona, meteorite, the excavator of Meteor Crater, is the only other iron meteorite known to contain these high-pressure minerals, and their occurrence in that meteorite has been explained as the result of shock-induced transformation of graphite, most probably at the moment of terrestrial impact and disintegration of the projectile during crater formation3–6. The suggestion7 that formation was by high gravitational pressure has not been accepted. Virtually identical diamond–lonsdaleite-containing material in ALHA77283 occurs in a meteorite specimen with a well developed heat-altered zone produced by atmospheric ablation. It seems, therefore, that the diamond and lonsdaleite were present in the meteoroid before its final ablative passage through the atmosphere and soft landing on the ground. The shock event that produced these high pressure phases, therefore, must have taken place on its parent body or have been associated with the disruption of that body. Here we present the metallographic and X-ray diffraction data on which this conclusion is based.

Antarctic Meteorite Program

The promise of substantially increasing knowledge about young igneous events in meteorite parent bodies was made with the discovery of two rare Antarctic achondrites during the 1979–1980 austral summer season. The NSF‐sponsored program to recover meteorites from Antarctica will continue during the 1980–1981 season along the Transantarctic Mountains near McMurdo Station. The search will concentrate on an ice field near Reckling Peak, about 260 km northwest of McMurdo.As in past seasons, all Antarctic finds will be returned to the Johnson Space Center in Houston for classification and curation. Many of the 27 meteorite specimens returned in 1979 have been tentatively classified; some scientifically exciting meteorites have been identified, including six achondrites. For example, Elephant Moraine A79001 is a 7.9‐kg specimen that appears to be closely related to the Shergotty, India, and the Allan Hills A77005 meteorites. This rare class of achondrite sparks interest among meteorite investigators: The meteorites show similarities to terrestrial materials in their abundances of several elements and in the oxidation state. They apparently experienced igneous differentiation in recent solar system history. In addition, the Elephant Moraine specimen may be the first meteorite found to exhibit a mineral and textural gradient produced during igneous differentiation.

3. Asteroid Surface Materials from Reflectance Spectroscopy: A Review

The quality and quantity of asteroidal spectral reflectance data has increased rapidly in recent years. This data can be either (a) classified into spectral, polarization and/or albedo groups (e.g., ‘C’, ‘S’, etc.) which should tend to lump together grossly similar materials, or (b) interpreted utilizing laboratory and theoretical understanding of spectral features (e.g., absorption bands, continuum shape and slope) which are diagnostic of mineralogy or mineral chemistry. Mineral assemblages have been identified on asteroid surfaces which are comparable to most known meteorite types or which have undergone the types of processes (e.g., melting and differentiation) necessary to produce the meteoritic assemblages. The ordinary chondrites, which dominate the meteoritic flux reaching the Earth’s surface, are very rare or absent on Main Belt asteroids but appear common on the small asteroids which approach or cross the orbit of the Earth. The present interpretations of asteroidal spectra are not yet quantitative enough to permit the evaluation of specific asteroids as the sources bodies of particular meteorite specimens in terrestrial collections.

A Comparison of the Noble Gases in Three Meteorite Specimens Labeled Springfield

The abundance and isotopic composition of the noble gases were measured in three Spring-field specimens identified by the Denver Museum of Natural History with numbers 7029, 379.13 and 6040. The latter specimen contains more cosmogenic noble gas isotopes than the other two specimens and the abundance pattern of trapped noble gases in specimen 6040 is distinct from that in the other two specimens. Specimen 7029 contains about seven times as much radiogenic 40Ar and about four times as much radiogenic 129Xe as does specimen 379.13. These results indicate that the three specimens did not come from a single meteoroid.

Spectral reflectance characteristics of the meteorite classes

Spectral reflectance curves (0.35–2.5 μm) have been measured for about 150 individual meteorite specimens which represent nearly all the types and subtypes of meteorites present in terrestrial meteorite collections. The spectra of members of each meteorite class are discussed in terms of the composition, abundance, and distribution of the component mineral phases. The range of meteoritic minerals is divided into four classes based on the optical properties of a mineral as defined by the optical density and conductivity of that mineral. These classes are (1) metals (e.g., the Ni-Fe minerals taenite, kamacite, etc.), (2) dielectric transparent phases which contain transition metal ions (Fe2+, Ti3+, etc.) (e.g., the common rock-forming silicates pyroxene, olivine, feldspar), (3) dielectric transparent phases which do not contain transition metal ions (e.g., the pure magnesium enstatite pyroxenes of enstatite chondrites and achondrites), and (4) opaque semiconductor phases (e.g., troilite (FeS), carbon, and carbon compounds typical of the carbonaceous chondrites). The mixing of phases follows the rule that the spectral contribution of a phase at a given wavelength is proportional to the relative optical density of that phase times the effective abundance of the phase. The important results of this study are as follows: (1) The spectral reflectance curves of a meteorite class, representing a particular mineral assemblage and metamorphic grade, do not differ significantly. (2) The variations between the spectra of different meteorite types are significant and are understandable in terms of differences in the composition, abundance, and distribution of the component mineral phases. These variations are of sufficient magnitude to permit discrimination of meteorite types from spectral data. (3) There exist a series of diagnostic features in the spectrum of a meteoritic material (absorption band presence, position, symmetry, and intensity as well as the continuum slope, curvature, and inflection points) which can be utilised in the general interpretation of telescopic spectral reflectance measurements of asteroids. (4) The positions of the 1.0- and 2.0-μm absorption features common in meteoritic materials are sensitive indicators of pyroxene compositions and of the olivine/pyroxene ratio. (5) The physical properties of a surface material (particle size, packing, illumination angle) for a reasonable range of these parameters do not significantly affect the normalized spectral reflectance curve measured for that material.

14C- 39Ar Me correlations in chondrites and their pre-atmospheric size

Cosmogenic 14C has been measured in 12 chondrites and the stone phase of the mesosiderite Bondoc. For the chondrites analysed the activities vary between 44 and 72 dpm/kg; the low value of (4.5 ± 0.9) dpm/kg for Bondoc is essentially due to its large pre-atmospheric size and not to a terrestrial age of several half-lives of 14C. In eight cases 39Ar in the metal phase from the same meteorite specimens had been measured previously. The results are combined to derive the pre-atmospheric radii R 0 of the meteoroids and depth of burial of the samples investigated. Values of R 0 between 35 and 82 cm are obtained; of 14 samples ten came from a depth of 10 cm or less. The preponderance of samples from shallow depths is ascribed to asymmetrical ablation losses of the meteoroids during their passage through the atmosphere. A compilation of all published 14C concentrations in chondrites shows that the variations between different specimens from the same meteorites are almost as large as those for samples from different meteorites. Thus, there is no need to invoke different orbits of the meteoroids and a strong spatial gradient in the primary cosmic-ray intensity to explain variations of low-energy-produced cosmogenic nuclides in different meteorites.

Non-destructive determination of nickel in iron meteorites

Application of a portable radioisotope X-ray fluorescence analyser for the determination of nickel in iron meteorites is described. The error of the XRF method was ±0.5% Ni at the 95% confidence level, which was confirmed by comparison with the results of other authors. In spite of limited accuracy this version of the radioisotope XRF method may find a wide application in meteorite studies, for rapid and non-destructive verification and classification of collected meteorite specimens.

Identification of the Hydrated Iron Oxide Mineral Akaganéite in Apollo 16 Lunar Rocks

Apollo 16 rocks contain rustlike alteration. A mass of rust-colored, iron-rich crystals forming a grain 30 µm in diameter in rock 66095 has been identified by x-ray diffraction as akaganeite (β FeOOH). Other altered polycrystalline masses of less diameter are found associated with native FeNi metal grains. Akaganeite is known to occur in meteorite specimens, resulting from the oxhydration of lawrencite (FeCl 2 ) and native FeNi upon exposure to water vapor. The occurrence of akaganeite in the Apollo 16 rocks is essentially the same as in meteorites, and a similar process of alteration in an oxidizing environment is posulated for its origin. All or at least most of the akaganeite formed as a direct result of contamination by terrestrial water vapor of FeCl 2 -bearing lunar rocks.

A CENSUS OF THE METEORITES OF ROOSEVELT COUNTY, NEW MEXICO

In the five years from June, 1967, to June, 1972, a total of 99 meteorites were found in Roosevelt County, New Mexico and in adjoining Curry County. Of this number, 74 were found by one man. The finds include two achondrites, one pallasite, one carbonaceous chondrite, and 95 chondrites. They appear to represent more than 50 separate meteorite falls. The finding of a large number of meteorites in a small area provides data for an estimate of the probable quantity and average size of the meteorite specimens reaching the earth. The problems involved in allocating a total of 17 available local place names among more than 50 meteorite falls are discussed.

Hardness of kamacite and shock histories of 119 meteorites

Use of metallographic and X-ray diffraction techniques to study the shock histories of 119 iron and stony-iron meteorites, and measurement of the hardness of kamacite in these specimens and in artificially shocked-unannealed and annealed meteorite specimens. Shock increases kamacite hardness, but complications introduced by other physical and chemical properties of meteorites limit its utility as a shock indicator. About 50% of the meteorites studied show evidence for preterrestrial shock loading to pressures of greater than or equal to 130 kb, and 40% have not been shocked to such high pressures. The remaining meteorites have been heat-altered in such a way that their shock histories cannot be determined explicitly. These results, together with those obtained previously, indicate that the plurality, if not the majority, of all iron and stony-iron meteorites sampled by the earth were shocked to pressures of greater than or equal to 130 kb during preterrestrial collisions between asteroidal-sized objects.

THE RANSOM METEORITES

A number of stony meteorite specimens, presumably from a single fall, have been recovered from an area about 5–6 miles north of Ransom, Kansas. This paper presents a map of discovery locations, so far as known. Megascopic appearance, external and internal, of a typical (?) specimen is described. The Ransom meteorite has already been classified as an olivine‐bronzite chondrite — chemical group H of Van Schmus and Wood. Features observed in thin section are characteristic of petrologic type 4