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.     

Oral Histories in Meteoritics and Planetary Science – XVII: Joseph Goldstein

Abstract– In this interview, Joseph Goldstein ( Fig. 1 ) recounts how he became interested in meteorites during his graduate studies working with Robert Ogilvie at MIT. By matching the Ni profiles observed across taenite fields in the Widmanstätten structure of iron meteorites with profiles he computed numerically he was able to determine cooling rates as the meteorites cooled through 650–400 °C. Upon graduating, he worked with a team of meteorite researchers led by Lou Walter at Goddard Space Flight Center where for 4 years he attempted to understand metallographic structures by reproducing them in the laboratory. Preferring an academic environment, Joe accepted a faculty position in the rapidly expanding metallurgy department at Lehigh University where he was responsible for their new electron microprobe. He soon became involved in studying the metal from lunar soils and identifying the metallic component from its characteristic iron and nickel compositions. Over the next two decades he refined these studies of Ni diffusion in iron meteorites, particularly the effect of phosphorus in the process, which resulted in superior Fe‐Ni‐P phase diagrams and improved cooling rates for the iron meteorites. After a period as vice president for research at Lehigh, in 1993 he moved to the University of Massachusetts to serve as dean of engineering, but during these administrative appointments Joe produced a steady stream of scientific results. Joe has served as Councilor, Treasurer, Vice President, and President of the Meteoritical Society. He received the Leonard Medal in 2005, the Sorby Award in 1999, and the Dumcumb Award for in 2008.

Figure 1 Open in figure viewer PowerPoint Joseph Goldstein.     

METEORITIC METAL IN APOLLO 16 SAMPLES

One hundred metallic particles from Apollo 16 soils (61181, 65701) and rocks (60018, 60315, 66055) have been investigated microscopically and by electron microprobe analysis. Their cobalt content indicates a meteoritic origin for all but one particle. However, most contain more phosphorus than typical meteoritic metal, possibly due to the reduction of phosphates in the lunar rocks. Compositions of coexisting kamacite and schreibersite indicate temperatures of about 550–650°C which are thought to have occurred during metamorphism. The bulk nickel content of the lunar metal is somewhat low by comparison with most iron meteorites or the metallic component of common stony meteorites. However, this may be due to compositional changes that occurred after emplacement in the lunar surface layer.     

Meteorites from Mongolia

Abstract— The mineralogy and composition of six Mongolian meteorites were studied in some detail. Previously, only limited information existed about these rocks, and some were still unclassified. The six meteorites include three ordinary chondrites and three irons. The ordinary chondrite Adzhi-Bogdo (stone) is a regolith breccia (LL3–6) containing various types of clasts (some of foreign origin) embedded within a fine-grained clastic matrix. Tugalin Bulen (H6) and Noyan Bogdo (L6) meteorites are typical, well-metamorphosed ordinary chondrites. Adzhi-Bogdo (iron) has to be regarded as an IA iron meteorite like Campo del Cielo or Canyon Diablo; although the sample studied had been heated to about 900 °C–950 °C some time in the past, thus eradicating all original structural elements. Manlai is structurally closely related to the IIC iron meteorites; but based on its chemistry, which does not fit into this group, it is suggested that Manlai is an anomalous iron meteorite. The third iron, Sargiin Gobi, is certainly a normal member of the IA iron meteorites. The concentrations and isotopic compositions of He, Ne, and Ar were measured for all meteorites and their gas retention ages and exposure ages are discussed.     

FTIR 2–16 micron spectroscopy of micron‐sized olivines from primitive meteorites

Abstract— Infrared spectra of mineral grains from primitive meteorites could be useful for comparison with astronomical infrared spectra since some of their grains might be similar to those formed in the planet‐forming disks around young stars or in the envelopes surrounding late‐type stars. To assess the usefulness of meteorite spectra, olivine grains separated from primitive meteorites have been analyzed using FTIR microscope techniques in the 2–16 μm wavelength range. The sub‐micron sizes of the grains made a complex preparation process necessary. Five characteristic bands were measured near 11.9, 11.2, 10.4, 10.1, and 10.0 μm. The results of 59 analyses allow the calculation of band positions for meteoritic olivines as a function of their iron and magnesium contents. Comparison of the meteoritic results with astronomical data for comets and dust around young and old stars, which exhibit bands similar to the strongest infrared bands observed in the grains (at 11.2 μm), show that the spectral resolution of the astronomical observations is too low to ascertain the exact iron and magnesium (Mg: Fe) ratio of the dust in the 8–13 μm wavelength range.     

FOUR NEW IRON METEORITE FINDS

Four new irons are described; Buenaventura (IIIB) from Chihuahua, Mexico: mass 114 kg; Denver City (anomalous) from Texas, USA: mass 26.1 kg; Kinsella (IIIB) from Alberta, Canada: mass 3.7 kg; and Tacoma (IA) from Washington, USA: mass 17 g. Denver City is unique, i.e., not related to any other known iron. Tacoma is the smallest iron meteorite recorded. All were purchased for the UCLA collection following a publicity drive for new meteorites     

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:     

Thallium in meteorites

Abstract— Thallium has been quantified in 50 iron meteorites and 6 chondrites using a combination of solvent extraction and graphite furnace atomic absorption spectrometry. The accuracy of the data was checked by analysis of two iron meteorites by laser-excited ICP mass spectrometry. The Tl abundance values for irons appear to be the first recorded and show that the Tl content allows for taxonomic separation of several groups on Tl vs. Ni abundance plots. The Tl content of irons is inversely correlated with abundances of platinum group metals such as Ir, Pt, and Rh and, in this respect, behaves like Pd and As that favour sulphur-rich phases in meteorites. Analysis of carbonaceous chondrites showed a 30-fold enrichment of Tl compared with ordinary chondrites.     

Natural variations in the rhenium isotopic composition of meteorites

Rhenium is an important element with which to test hypotheses of isotope variation. Historically, it has been difficult to precisely correct the instrumental mass bias in thermal ionization mass spectrometry. We used W as an internal standard to correct mass bias on the MC‐ICP‐MS, and obtained the first precise δ¹⁸⁷Re values (~±0.02‰, 2SE) for iron meteorites and chondritic metal. Relative to metal from H chondrites, IVB irons are systematically higher in δ¹⁸⁷Re by ~0.14 ‰. δ¹⁸⁷Re for other irons are similar to H chondritic metal, although some individual samples show significant isotope fractionation. Since ¹⁸⁵Re has a high neutron capture cross section, the effect of galactic cosmic‐ray (GCR) irradiation on δ¹⁸⁷Re was examined using correlations with Pt isotopes. The pre‐GCR irradiation δ¹⁸⁷Re for IVB irons is lower, but the difference in δ¹⁸⁷Re between IVB irons and other meteoritic metal remains. Nuclear volume‐dependent fractionation for Re is about the right magnitude near the melting point of iron, but because of the refractory and compatible character of Re, a compelling explanation in terms of mass‐dependent fractionation is elusive. The magnitude of a nucleosynthetic s‐process deficit for Re estimated from Mo and Ru isotopes is essentially unresolvable. Since thermal processing reduced nucleosynthetic effects in Pd, it is conceivable that Re isotopic variations larger than those in Mo and Ru may be present in IVBs since Re is more refractory than Mo and Ru. Thus, the Re isotopic difference between IVBs and other irons or chondritic metal remains unexplained.     

GEOLOGY AND TERRESTRIAL AGE OF THE DERRICK PEAK METEORITE OCCURRENCE,ANTARCTICA

Sixteen iron meteorites together weighing 320 kg were recovered from the north-eastern flank of Derrick Peak, northern Britannia Range, Antarctica (156°30′E, 80°05′S), in December 1978. The well preserved meteorites rested cleanly upon an elevated, lag covered, glacially carved post-Middle Miocene to Pliocene bench cut into Devonian orthoquartzites intruded by Jurassic dolerite, and at a lower elevation upon Middle Pleistocene glacial drifts. In considering that the irons are in situ, and based on drift correlations along the Transantarctic Mountains, a maximum terrestrial age of 200,000–300,000 years B.P. is favoured.     

Thermal and impact histories of reheated group IVA,IVB, and ungrouped iron meteorites and their parent asteroids

Abstract– The microstructures of six reheated iron meteorites—two IVA irons, Maria Elena (1935), Fuzzy Creek; one IVB iron, Ternera; and three ungrouped irons, Hammond, Babb’s Mill (Blake’s Iron), and Babb’s Mill (Troost’s Iron)—were characterized using scanning and transmission electron microscopy, electron‐probe microanalysis, and electron backscatter diffraction techniques to determine their thermal and shock history and that of their parent asteroids. Maria Elena and Hammond were heated below approximately 700–750 °C, so that kamacite was recrystallized and taenite was exsolved in kamacite and was spheroidized in plessite. Both meteorites retained a record of the original Widmanstätten pattern. The other four, which show no trace of their original microstructure, were heated above 600–700 °C and recrystallized to form 10–20 μm wide homogeneous taenite grains. On cooling, kamacite formed on taenite grain boundaries with their close‐packed planes aligned. Formation of homogeneous 20 μm wide taenite grains with diverse orientations would have required as long as approximately 800 yr at 600 °C or approximately 1 h at 1300 °C. All six irons contain approximately 5–10 μm wide taenite grains with internal microprecipitates of kamacite and nanometer‐scale M‐shaped Ni profiles that reach approximately 40% Ni indicating cooling over 100–10,000 yr. Un‐decomposed high‐Ni martensite (α₂) in taenite—the first occurrence in irons—appears to be a characteristic of strongly reheated irons. From our studies and published work, we identified four progressive stages of shock and reheating in IVA irons using these criteria: cloudy taenite, M‐shaped Ni profiles in taenite, Neumann twin lamellae, martensite, shock‐hatched kamacite, recrystallization, microprecipitates of taenite, and shock‐melted troilite. Maria Elena and Fuzzy Creek represent stages 3 and 4, respectively. Although not all reheated irons contain evidence for shock, it was probably the main cause of reheating. Cooling over years rather than hours precludes shock during the impacts that exposed the irons to cosmic rays. If the reheated irons that we studied are representative, the IVA irons may have been shocked soon after they cooled below 200 °C at 4.5 Gyr in an impact that created a rubblepile asteroid with fragments from diverse depths. The primary cooling rates of the IVA irons and the proposed early history are remarkably consistent with the Pb‐Pb ages of troilite inclusions in two IVA irons including the oldest known differentiated meteorite ( Blichert‐Toft et al. 2010 ).     

Impact-induced devolatilization of four ungrouped ataxites and the formation of a silica glass spherule in ALHA77255

Allan Hills A77255, Babb's Mill (Blake's Iron), Nordheim, and Chinga are ungrouped ataxitic iron meteorites that are similar to the IAB group of noncarbonaceous-type irons in their concentrations of common and refractory siderophile elements. Mo-isotopic data show that ALHA77255, Nordheim, and Chinga are carbonaceous-type (CC) irons. (The Mo-isotopic composition of Babb's Mill [Blake's Iron] has not yet been measured, but it also seems likely to be a CC iron.) Relative to mean IAB irons, these four ataxites are severely depleted in moderately volatile elements: Ga, >99%; Ge, >99%; Cu, 79%–97%; As, 70%–96%; P, 76%–90%. These samples were probably devolatilized by major collisions on separate parent asteroids (consistent with fractional crystallization modeling showing they are unlikely to be derived from the same metallic core). Collisionally induced devolatilization of ALHA77255 likely facilitated the formation of a 5-mm diameter silica–glass spheroid in this meteorite. The spheroid may have formed by a complex process involving impact-induced vaporization of mantle material in its parent asteroid, followed by fractional condensation.     

The Mazapil meteorite: From paradigm to periphery

Abstract— The remarkable fact about the Mazapil meteorite is that it fell on the same night, in 1885, that the Andromedid meteor shower underwent a spectacular outburst. The simultaneity of these two events has driven speculation ever since. From ?1886 to ?1950 the circumstances of the Mazapil fall were taken, by a number of researchers, as the paradigm that demonstrated the fact that comets were actually swarms of meteoritic boulders. Beginning ?1950, however, most researchers began to adopted the stance that the timing of the Mazapil fall was nothing more than pure coincidence. The reason behind this change in interpretation stemmed from, amongst other factors, the fact that none of the prominent annual meteor showers could be clearly shown to deliver meteorites. Also, with the introduction of the icy‐conglomerate model for cometary nuclei, by F. Whipple in the early 1950s, it became increasingly clear that only exceptional circumstances would allow for the presence of large meteoritic bodies in cometary streams. Further, by the mid 1960s it had been shown that meteorites could, in fact, be delivered to the Earth from the main belt asteroid region via gravitational resonances. With the removal of the dynamical “barrier” against the delivery of meteorites from the asteroid region, the idea that the Mazapil meteorite could have been part of the Andromedid stream fell into complete disfavor. This being said, we nonetheless present the results of a study concerning the possible properties of the parent object to the Mazapil meteorite based upon the assumption that it was a member of the Andromedid stream. This study is presented to illustrate the point that while cometary showers do not yield meteorites on the ground, this does not, in fact, substantiate the argument that no meteoritic bodies reside in cometary streams. Indeed, we find no good reason to suppose that an object with the characteristics of the Mazapil meteorite could not have been delivered from the Andromedid stream. However, we argue that upon the basis of the actual reported observations and upon the scientific maxim of minimized hypothesis and least assumption it must be concluded that the timing of the fall of the Mazapil meteorite and the occurrence of the Andromedid outburst were purely coincidental.     

Buddha from space—An ancient object of art made of a Chinga iron meteorite fragment*

Abstract– The fall of meteorites has been interpreted as divine messages by multitudinous cultures since prehistoric times, and meteorites are still adored as heavenly bodies. Stony meteorites were used to carve birds and other works of art; jewelry and knifes were produced of meteoritic iron for instance by the Inuit society. We here present an approximately 10.6 kg Buddhist sculpture (the “iron man”) made of an iron meteorite, which represents a particularity in religious art and meteorite science. The specific contents of the crucial main (Fe, Ni, Co) and trace (Cr, Ga, Ge) elements indicate an ataxitic iron meteorite with high Ni contents (approximately 16 wt%) and Co (approximately 0.6 wt%) that was used to produce the artifact. In addition, the platinum group elements (PGEs), as well as the internal PGE ratios, exhibit a meteoritic signature. The geochemical data of the meteorite generally match the element values known from fragments of the Chinga ataxite (ungrouped iron) meteorite strewn field discovered in 1913. The provenance of the meteorite as well as of the piece of art strongly points to the border region of eastern Siberia and Mongolia, accordingly. The sculpture possibly portrays the Buddhist god Vai?ravana and might originate in the Bon culture of the eleventh century. However, the ethnological and art historical details of the “iron man” sculpture, as well as the timing of the sculpturing, currently remain speculative.     

The meteoritic origin of Tutankhamun's iron dagger blade

Scholars have long discussed the introduction and spread of iron metallurgy in different civilizations. The sporadic use of iron has been reported in the Eastern Mediterranean area from the late Neolithic period to the Bronze Age. Despite the rare existence of smelted iron, it is generally assumed that early iron objects were produced from meteoritic iron. Nevertheless, the methods of working the metal, its use, and diffusion are contentious issues compromised by lack of detailed analysis. Since its discovery in 1925, the meteoritic origin of the iron dagger blade from the sarcophagus of the ancient Egyptian King Tutankhamun (14th C. BCE) has been the subject of debate and previous analyses yielded controversial results. We show that the composition of the blade (Fe plus 10.8 wt% Ni and 0.58 wt% Co), accurately determined through portable x‐ray fluorescence spectrometry, strongly supports its meteoritic origin. In agreement with recent results of metallographic analysis of ancient iron artifacts from Gerzeh, our study confirms that ancient Egyptians attributed great value to meteoritic iron for the production of precious objects. Moreover, the high manufacturing quality of Tutankhamun's dagger blade, in comparison with other simple‐shaped meteoritic iron artifacts, suggests a significant mastery of ironworking in Tutankhamun's time.     

Mass‐dependent fractionation of nickel isotopes in meteoritic metal

Abstract— We measured nickel isotopes via multicollector inductively coupled plasma mass spectrometry (MC‐ICPMS) in the bulk metal from 36 meteorites, including chondrites, pallasites, and irons (magmatic and non‐magmatic). The Ni isotopes in these meteorites are mass fractionated; the fractionation spans an overall range of ～0.4‰ amu^?1. The ranges of Ni isotopic compositions (relative to the SRM 986 Ni isotopic standard) in metal from iron meteorites (～0.0 to ～0.3‰ amu^?1) and chondrites (～0.0 to ～0.2‰ amu^?1) are similar, whereas the range in pallasite metal (～–0.1 to 0.0‰ amu^?1) appears distinct. The fractionation of Ni isotopes within a suite of fourteen IIIAB irons (～0.0 to ～0.3‰ amu^?1) spans the entire range measured in all magmatic irons. However, the degree of Ni isotopic fractionation in these samples does not correlate with their Ni content, suggesting that core crystallization did not fractionate Ni isotopes in a systematic way. We also measured the Ni and Fe isotopes in adjacent kamacite and taenite from the Toluca IAB iron meteorite. Nickel isotopes show clearly resolvable fractionation between these two phases; kamacite is heavier relative to taenite by ～0.4‰ amu^?1. In contrast, the Fe isotopes do not show a resolvable fractionation between kamacite and taenite. The observed isotopic compositions of kamacite and taenite can be understood in terms of kinetic fractionation due to diffusion of Ni during cooling of the Fe‐Ni alloy and the development of the Widmanstätten pattern.     

The catalog of the meteorite collection of the Italian Museum of Planetary Sciences in Prato (Italy)

For the first time, this paper presents to the planetary scientists' community the catalog of the meteorite collection preserved at the Italian Museum of Planetary Sciences (Museo Italiano di Scienze Planetarie, henceforth MISP) in Prato (Italy). Founded in 2005, MISP is a type specimen official repository approved by the Nomenclature Committee of the Meteoritical Society. It represents one of the few museums worldwide entirely devoted to planetary sciences. The catalog of its meteorite collection encompasses 430 meteorites for a total of 1536 specimens, including 291 thin sections, 184 thick sections, and 278 specimens that MISP has classified. Furthermore, MISP is currently classifying 57 other meteorites. Some samples were found during meteorite recovery expeditions in hot deserts, promoted by MISP in collaboration with diverse Italian universities and national research institutions. MISP also keeps an impact rocks collection comprising 257 samples. In a country like Italy, where most of the collected meteorites are housed in museums whose catalogs are not available online, the publication of the MISP meteorite collection catalog, together with the catalog of the impact rocks collection, represents not only a significant scientific primary source but also a remarkable tool for disseminating meteoritics to nonresearch audiences in educational activities and citizen science projects.     

The formation of the Widmanstätten structure in meteorites

Abstract— We have evaluated various mechanisms proposed for the formation of the Widmanstätten pattern in iron meteorites and propose a new mechanism for low P meteoritic metal. These mechanisms can also be used to explain how the metallic microstructures developed in chondrites and stony‐iron meteorites. The Widmanstätten pattern in high P iron meteorites forms when meteorites enter the three‐phase field α + γ + Ph via cooling from the γ + Ph field. The Widmanstätten pattern in low P iron meteorites forms either at a temperature below the (α + γ)/(α + γ + Ph) boundary or by the decomposition of martensite below the martensite start temperature. The reaction γ → α + γ, which is normally assumed to control the formation of the Widmanstätten pattern, is not applicable to the metal in meteorites. The formation of the Widmanstätten pattern in the vast majority of low P iron meteorites (which belong to chemical groups IAB‐IIICD, IIIAB, and IVA) is controlled by mechanisms involving the formation of martensite α₂. We propose that the Widmanstätten structure in these meteorites forms by the reaction γ → α₂ + γ → α + γ, in which α₂ decomposes to the equilibrium α and γ phases during the cooling process. To determine the cooling rate of an individual iron meteorite, the appropriate formation mechanism for the Widmanstätten pattern must first be established. Depending on the Ni and P content of the meteorite, the kamacite nucleation temperature can be determined from either the (γ + Ph)/(α + γ + Ph) boundary, the (α + γ)/(α + γ + Ph) boundary, or the M_s temperature. With the introduction of these three mechanisms and the specific phase boundaries and the temperatures where transformations occur, it is no longer necessary to invoke arbitrary amounts of under‐cooling in the calculation of the cooling rate. We conclude that martensite decomposition via the reactions γ → α₂ → α + γ and γ → α₂ + γ → α + γ are responsible for the formation of plessite in irons and the metal phases of mesosiderites, chondrites, and pallasites. The hexahedrites (low P members of chemical group IIAB) formed by the massive transformation through the reaction γ → α_m → α at relatively high temperature in the two‐phase α + γ region of the Fe‐Ni‐P phase diagram near the α/(α + γ) phase boundary.     

Campo del Cielo: A Campo by any other name

A sample of Campo del Cielo with any other name would have the same composition. During the last three decades, our instrumental neutron activation analyses (INAA) of many supposedly new iron meteorites have shown an anomalously large fraction to have compositions within the compositional field of the IAB‐MG iron Campo del Cielo. A plot of Ir versus Au provides the best discrimination; only two independent‐fall irons found after 1980 with good recovery documentation fall within the 90% contour ellipse around the centroid of this Campo field, and one of these is from Antarctica. Now (early 2018) a total of 36 other irons attributed to other geographical locations have compositions that cannot be resolved from the Campo compositional field. Because it is possible that some of these are actually independent falls, the Meteoritical Society Nomenclature Committee has chosen to assign about half these meteorites Nova XXX names used for meteorites whose discovery localities are not adequately documented. However, for Campo‐like irons with too little information (e.g., total weight not known) or for which no adequately large type specimens are available, the decision is to call them Campos with the working name used during the UCLA analysis. In the UCLA Meteorite Collection, they are cataloged together with the documented Campos.