Coarse Octahedrite Research Articles

A heavenly sword – forging a Campo del Cielo meteorite

Abstract After a thorough structural examination, a “Campo del Cielo” iron meteorite found in Argentina was forged at temperatures of about 1100 °C. This meteorite is classified as an IA group coarse octahedrite. Besides Fe, it also contains about 7 wt.% Ni and 1.5 wt.% Co, as well as small amounts of Mg, Si, Al, S, and P. Heat treatments above the eutectoid temperature induce a α-γ transformation of the present (Fe,Ni) solid solution. Owing to the retransformation that takes place upon cooling, the typical microstructure of the meteorite vanishes and a mainly ferritic polycrystalline microstructure forms (kamacite α-(Fe,Ni)). Only minor changes could be observed for the initially present taenite γ-(Fe,Ni). Schreibersite, also referred to as rhabdite (Fe,Ni)3P, melts and dissolves into the surrounding matrix. At high temperatures, locally present graphite likewise dissolves and cementite or martensite are formed upon cooling. Changes of other phases such as troilite (FeS) or lawrencite (Fe,Ni)Cl2 could not be detected. Given an initial weight of the meteorite fragment of approx. 1.5 kg, the intention was to manufacture a sword. However, since the meteorite broke apart during forging, only a knife could be manufactured.

Campo del Cielo – an Iron Meteorite found in Argentina

Abstract Fragments of the “Campo del Cielo” meteorite were first reported by conquistadores in Argentina in as early as 1576. This meteorite belongs to the group of iron meteorites and is classified as a group IA coarse octahedrite. The use of meteoric iron to make objects of daily use or hunting weapons in prehistoric times is only confirmed by very few finds. Metallographic examinations were performed to assess if it was realistic and in fact feasible to process meteoric iron. The bulk of the examined “Campo del Cielo” meteorite fragment found in Argentina is kamacite (α-Fe) with approx. 5.3 wt.% of dissolved Ni. Graphite was also detected in addition to various non-metallic phases. Due to high temperatures during processing, graphite can dissolve and a steel microstructure would form as a result.

NEW DATA ON THE STRUCTURE AND AGE OF THE KAALI METEORITE CRATERS (ISLAND OF SAAREMAA, ESTONIA)

Kaali meteorite craters are located on the Island of Saaremaa, 18 km northeast of its chief town Kuressaare, being the first established meteorite craters in Europe. Nine meteorite craters formed about 7500 years BP as a result of single iron meteorite falling apart, which was a typical coarse octahedrite with Fe/Ni ratio being equal to 91.5/8.3. Craters are spread within a wildlife reserve of the total area about 50 ha. Craters were formed in a two-layered target rock: till and dolomite. The diameter of the main crater is 105–110 m.

The Dunganville (New Zealand) meteorite: an iron octahedrite (Note)

The Dunganville meteorite, found near Greymouth, South Island, is a coarse octahedrite Class Og, Chemical Group 1. Electron probe analyses of .kamacite, taenite, and schreibersite are given, and a bulk analysis obtained by wet chemical and XRF methods is included. Very small, scarce inclusions of troilite contain grains of a pure end member chromite. Dunganville is the largest meteorite yet found in New Zealand; weight 50.2 kg, dimensions 35x21 × 16 cm.

Ulasitai: A new iron meteorite likely paired with Armanty (IIIE)

Abstract— The Ulasitai iron was recently found about 130 km southeast to the find site of the Armanty (Xinjiang, IIIE) meteorite. It is a coarse octahedrite with a kamacite bandwidth of 1.2 ± 0.2 (0.9–1.8) mm. Plessite is abundant, as is taenite, kamacite, cohenite, and schreibersite with various microstructures. Schreibersite is Ni‐rich (30.5–55.5 wt%) in plessite or coexisting with troilite and daubreelite, in comparison with the coarse laths (20.6–21.2 wt%) between the Widmanstätten pattern plates. The correlation between the center Ni content and the half bandwidth of taenite suggest a cooling rate of ˜20 °C/Myr based on simulations. The petrography and mineral chemistry of Ulasitai are similar to Armanty.The bulk samples of Ulasitai were measured, together with Armanty, Nandan (IIICD), and Mundrabilla (IIICD), by inductively coupled plasma atomic emission spectrometry (ICP‐AES) and mass spectrometry (ICP‐MS). The results agree with literature data of the same meteorites, and our analyses of four samples of Armanty (L1, L12, L16, L17) confirm a homogeneous composition (Wasson et al. 1988). The bulk composition of Ulasitai is identical to that of Armanty, both plotting within the IIIE field. We classify Ulasitai as a new IIIE iron and suggest that it pairs with Armanty.

Mineralogical and Geochemical Study of Zhaoping, Xifu and Hami Iron Meteorites

The mineralogy and bulk chemical compositions of three iron meteorites (Zhaoping, Xifu and Hami) recently found in China are reported here and are classified on the basis of their bulk chemical compositions. Zhaoping contains 93.4 mg/g Ni, 85.9 μg/g Ga, 418 μg/g Ge, 5.24 mg/g Co, 1.94 μg/g Ir, 0.774 μg/g W, and 1.62 μg/g Au and belongs to the low-Ni, low-Au subgroup of IAB. It is a coarse octahedrite and consists of kamacite, taenite, troilite, schreibersite and cohenite. The cohenite has entirely decomposed to graphite and low-Ni kamacite in our samples. Zhaoping contains some inclusions of Mn-free sarcopside which were rarely reported in IAB iron meteorites. Xifu has 74.1 mg/g Ni, 58.8g μg/g Ga, 150 μg/g Ge, and 0.913 μg/g W. Xifu is a member of group IIICD iron meteorite. Like most of IIICD irons, Xifu is a coarsest octahedrite with kamacite bandwidth larger than 3mm, and contains kamacite, taenite and schreibersite. Carbides and graphite are not found in the sample because of its being heterogeneous. Hami has 106 mg/g Ni, 5.36 mg/g Co and 0.922 μg/g Ir. We did not obtain the Ga and Ge contents in Hami because of their low concentrations and the limited precision of the INAA technique. Hami is an unclassified iron meteorite on the basis of the contents of other trace elements, structure and mineralogy. On mineralogy and structure, Hami resembles Rafruti, another unclassified iron meteorite.

Toronto, a new Canadian meteorite

Abstract— A specimen easily identified as an iron meteorite was first authenticated at the University of Toronto. Although the finder, Karl Heinz, is deceased, it is believed that the meteorite was found on a canoe trip in the Province of Québec. The 2.715 kg main mass is weathered and has no preserved heat‐affected zone, although the external shape has a suggestion of regmaglypts, providing evidence that the specimen is a new find. The meteorite is a coarse octahedrite, with kamacite bandwidth 1.64 ± 0.56 mm. Neutron activation analysis yielded Ni 70.4 mg/g, Ge 372 μg/g, Ga 87 μg/g, and Ir 2.55 μg/g, clearly indicating that it is a member of group IAB with composition similar to that of Canyon Diablo. However, of 13 minor and trace elements, As, Au, Ir, Pt, Re, and Sb are more than three standard deviations from well‐established Canyon Diablo means, and Ge differs by nearly three standard deviations. The meteorite thus appears to be a new find. The name is in recognition of the University of Toronto, where the meteorite was first examined.

Two new iron meteorites from the Province of Québec, Canada

Abstract— Two iron meteorites, identified in 1994, have been recovered from the Province of Québec, Canada. Lac Dodon is a coarse octahedrite of 800 g, displaying only minor evidence of terrestrial weathering. A heat‐affected zone up to 1 mm thick is fairly well preserved. Penouille is a medium octahedrite of 72.5 g that was recovered from an ocean beach. Traces of a heat‐affected zone are preserved. Analyses reveal that both meteorites are members of group IAB, although Penouille is in the Ni‐rich IB tail of the group.

The Lueders, Texas, IAB iron meteorite with silicate inclusions

Abstract The Lueders iron meteorite with silicate inclusions was recovered as a single specimen of ∼35.4 kg in Shackelford County, Texas, in 1973 and recognized as a meteorite in 1993. Siderophile element concentrations indicate chemical classification as a low‐Ni IAB iron meteorite closely related to Landes; like Landes, it has a Cu content ∼4σ above the main IAB‐IIICD trend and therefore we also designate Lueders as an anomalous member of IAB. The metallic host is composed of equigranular kamacite but with a suggestion of octahedral structure and with a bandwidth of 1.4 mm, suggesting structural classification as a coarse octahedrite (Og). The meteorite contains ∼23 wt% of roughly millimeter to centimeter‐sized angular silicate inclusions. Classification as a IAB is confirmed by O isotopic analysis of silicate inclusions. These inclusions contain an assemblage rich in silicates, troilite and graphite; lack certain minor phases (e.g., daubreelite); and have angular shapes. A variety of processes (e.g., fragmentation, partial melting, reduction) appear to have played a significant role in the formation of Lueders and all IAB iron meteorites. Petrologic and chemical differences confirm that Lueders is not paired with the widely distributed Odessa meteorite.

The Tianlin meteorite

Abstract Chemical data are reported for the Tianlin iron meteorite from south China. The meteorite is classified as a coarse octahedrite of group IA with complete decomposition of cohenite to ferrite and graphite.

A preliminary report of the Chisenga iron meteorite, Malawi

An iron meteorite fell on the afternoon of 17th January, 1988, in the Chisenga area, Chitipa district (10° 03′ 34″ S,33° 23′ 42″ E). The meteorite was immediately recovered. It is a triangular body 16 cm high and 15 cm on its base. The meteorite weighed 3.92 kg on recovery. Its surface has spectacular smooth thumb print-like depressions and is entirely covered by a black fusion crust. Chemical analysis has indicated 92.6% Fe, 6.2% Ni, 0.6% Co, 139 ppm Cr, 136 ppm Ag, 68 ppm Zn, 0.1 ppm Au, 0 ppm Pb, As and S. The meteorite crystallised as two phase kamacite and taenite. The Widmanstatten structure is composed of 1.5 mm wide kamacite bands and about 0.1 mm taenite bands. Nickel content indicates that the meteorite is close to Group IA and IIB of the chemical groups, while texture indicates that it is a coarse octahedrite. Shock before descending to earth and impact in flight and on landing resulted in fracturing. Terrestrial corrosion has attacked some of the nickel rich taenite-plessite bands.

Properties of the Guin ungrouped iron meteorite: the origin of Guin and of group-IIE irons

Guin is an ungrouped iron meteorite containing 45 μg/g Ga and 186 μg/g Ge. It is a coarse octahedrite with an unusually high Ni content (92.5 mg/g). Its metal composition is generally similar to irons in groups IAB and IIICD, but its closest relative is the Cruz del Aire ungrouped iron. Guin contains 6 ± 3 vol.% silicate inclusions that are petrologically and compositionally similar to those in IIE irons. The largest inclusion (2 × 4 cm) consists primarily of a shock-melted plagioclase-rich matrix surrounding large (1–15 mm), partly-melted augite grains. The oxygen isotopic composition of the inclusion ( δ 18O = 5.29‰; δ 17O = 3.87‰ ) is near the LL chondrite field. The Guin inclusion is similar in bulk composition to selected melt pocket glasses in ordinary chondrites produced in situ by preferential melting of plagioclase by shock compression. We suggest that the Guin assemblage formed by impact-melting on a chondritic parent body. Silicate inclusions in IIE irons share many petrologic and compositional (but not oxygen isotopic) characteristics with the Guin inclusions, suggesting that IIE irons also formed by impact-melting of chondritic materials. Individual IIE irons were probably derived from separate cratering events.

On the Distribution of Major and Trace Elements Between Metal and Phosphide Phases of Some Iron Meteorites

Abstract The concentrations of Fe, Ni, Co, P, Cu, Ga, Ge, Mo, Ru, Rh, Pd, W, Ir and Pt in the phosphides and the metal of the coarse octahedrites Campo del Cielo, Canyon Diablo, Cranbourne and Sardis, the coarsest octahedrite São Julião de Moreira and the hexahedrites Braunau and Lombard have been determined by spark source mass spectrometry. Striking differences are observed of the element contents between bulk meteorite and the phosphides as well as between the different phosphide modifications schreibersite and rhabdite. Extreme values are a 20 fold depletion of Ga and a 40 times higher content of Pd in the phosphides. A particularly strong correlation between the noble metal element content and size of phosphide aggregates is observed; it is shown that this correlation is not an artifact of the sample preparation but that is must be real.

ELEVEN NEW METEORITES FROM ANTARCTICA, 1976–1977

Basic petrographic, mineralogic, and chemical descriptions are given for all eleven meteorites recovered by the U.S.‐Japan team in Antarctica during the austral summer 1976–1977. The meteorites are: Mt. Baldr a (H6), Mt. Baldr b (H6), Allan Hills #1 (L6), Allan Hills #2 (coarsest octahedrite, chemical group IA), Allan Hills #3 (L6), Allan Hills #4 (LL3), Allan Hills #5 (eucrite), Allan Hills #6 (H6), Allan Hills #7 (L6), Allan Hills #8 (H6), and Allan Hills #9 (L6).

A scanning electron microscope (SEM) sturon me the magnetic domain structure of ion meteorites and their synthetic analogues.

Magnetic domain observations were carried out on iron meteorites and on sputter-deposited thin films of meteoritic composition (10, 20% Ni-Fe), by two SEM techniques: 1) high voltage (30kV) backscattered electron mode and 2) low-voltage (2kV) secondary electron image. To confirm and complement these, 3) Bitter-powder patterns were also observed in reflected-light microscopy. High energy SEM magnetic contrast revealed parallel-oriented arrays of stripe domains in kamacite (k) regions, at 60° (for ‹111› face) or 90° (for ‹100› face) to their taenite (t) boundaries, depending on the crystal orientation. Magnetic domain widths ranged from 15-25μm in the Gibeon meteorite (finest octahedrite, 8% Ni-Fe, average k-bandwidth 0.2mm) to 40-80μm in the Odessa meteorite (coarsest octahedrite, 7.29% Ni-Fe, 3.3mm k-bands). Finer domain substructure (-10μm) was resolved by Bitter-pattern microscopy in Odessa, as magnetic grids in each k grain, whose orientation was discontinuous across boundaries. Based on low-energy SEM observations of Gibeon, it appears that each micro-kamacite grain in plessite regions is a single domain. By the same technique, 1-5μm stripe domains separated by ≤0.5μm Bloch walls were resolved in a 20% Ni-Fe film and 0.2-2μum domains with 90° “elbow”-walls, typical of Fe3O4, were observed in a laboratory-produced Fe3O4 film. The much finer scale of magnetic domain structure in meteorites, by comparison with their metallographic-compositional features, may explain the presence of stable paleoremanence in the coarsely crystalline iron meteorites.The application of even higher-voltage (50kV) SEM to similar studies of terrestrial, lunar, and meteoritic materials promises to reveal the bulk domain-structure of their magnetic carriers and may thus afford a better understanding of their paleomagnetic record.

Isotope Analysis on Iron Meteorites with Ion Probe Mass Spectrometer

In order to investigate the isotopic effect of nickel which might have been brought into by the diffusion of nickel isotopes during the crystallization of an iron meteorite, the isotopic ratio 58Ni/60Ni and the nickel concentration were measured with the ion probe mass spectrometer. Krypton and argon ions were used as a primary ions, whose energy was 5 keV. The diameter and the current of the primary ion beam were 250 µm and 2×10-7 A on the surface of the sample target. Three iron meteorites, Odessa, Canyon Diablo and Hembury were analyzed. Two former samples belong to the class of coarse octahedrite, and the latter one medium octahedrite. The point-to-point analysis was carried out every 0.25 mm or 0.5 mm in the range of about 4 mm on the surface of the sample. The distribution of 58Ni/60Ni was likely to correlate to the nickel concentration in the case of Odessa and Canyon Diablo.

The Canyon Diablo meteorite

The giant diamond-containing Canyon Diablo meteorite is in composition a typical representative of the widespread group of iron meteorites — the coarse octahedrites. But it is unique in a number of scientifically important aspects. When it fell, it formed the Arizona (Barringer meteorite) crater (1220 m in diam), which is of the explosive type. The investigations of the shock recrystallization of the crater rocks and the meteoritic material are of importance for planetology, and in particular for the eludication of matter recrystallization conditions during the collisions of large cosmic bodies. The study of the diamonds contained in the Canyon Diablo meteorite is of importance to various branches of carbon cosmochemistry. The Canyon Diablo meteorite fell in Arizona, U.S.A., some tens of thousands years ago. However, the Arizona meteorite crater is well preserved owing to the semi-arid climatic conditions. Signs of shock recrystallization of the rocks — shatter cones, impactites, dense and super-dense silica modifications were revealed in the Arizona meteorite crater. Around the crater many samples of the Canyon Diablo iron meteorite have been found (at distances of up to 9 km from the crater), together with a great amount of finely dispersed meteorite matter. The total weight of the material attributed to the meteorite is put at 30 tons. A number of meteorite fragments have been oxidized to different degrees during terrestrial weathering. Typical samples of the Canyon Diablo meteorite are represented by coarse octahedrite matter with kamacite band widths of 1.8–2.2 mm. In many meteorite fragments, especially the fragments found on the crater rim, the Widmanstatten pattern has been destroyed as a result of the explosion which occurred when the meteorite hit the Earth. The meteorite is rich in accessory minerals (cohenite, schreibersite, troilite.). The Ni content is, in typical samples of the meteorite, about 7.16%, in rare, atypical, medium octahedrite samples the Ni content reached 8.2 %. In the content of trace elements the meteorite may be classified with the I Ga-Ge group. In the content of stable isotopes of elements there is no substantial difference between the Canyon Diablo meteorite and other octahedrites. Radioactive cosmogenic isotopes are represented by isotopes with a large half-life. The diamonds in the Canyon Diablo meteorite are unevenly distributed and are found inside the highly recrystallized meteorite fragments at the rim of the crater. Diamonds are present in the form of intergrowths of microcrystals, crystallite sizes are < 1μ, the sizes of the intergrowths reach 2–5 mm. Admixtures of graphite and the hexagonal diamond lonsdaleite are present in the intergrowths. From the evidence of shock recrystallization of the meteorite matter it would seem that the diamond containing fragments of the Canyon Diablo meteorite have undergone shock pressures of from 400 kbar to 1 mgbar at impact, at these pressures the diamonds would crystallise. The diamond-containing sample of the Canyon Diablo meteorite investigated by the author has experienced a shock pressure of up to 1 mgbar during the explosion.

The isotopic composition of ‘graphitic’ carbon from iron meteorites and some remarks on the troilitic sulfur of iron meteorites

The carbon isotopic composition of graphite inclusions and finely dispersed carbon from twelve iron meteorites has been studied. The analyses are given as parts permil deviations from the PDB standard. Forty-five analyses of inclusion-graphites from four coarse-grained octahedrites fall in the range from − 4.8 to − 8.2‰; within some of the inclusions a C 13 depletion toward the rim of the nodules is observed. Finely dispersed, residual carbon from four coarse octahedrites, obtained by dissolving the meteorite, shows distinctly lighter isotopic compositions ranging from −5.6 to −24.1%., probably representing a mixture of small inclusions and flakes as well as carbon contained in carbides or in solid solution in the nickel-iron. Graphite inclusions showing C 13 concentrations outside the above range for inclusion-graphites were found in 1. (1) two octahedrites with silicate inclusions, i.e., Four Corners (− 4.0%.) and Pine River (− 8.7%.). 2. (2) the hexahedrite Kendall County (−13.3 to −14.4%.). 3. (3) the ‘ataxite’ Dayton (−11.5 to −11-8%.). This suggests that the average carbon isotopic composition may not be identical for all iron meteorites. The large variability in the C 13 concentration encountered within individual irons contrasts with the isotopic constancy of sulfur observed in meteorites. It is proposed that the differences in the isotope distribution patterns of the two elements may be understood on the basis of the chemical phase relationships in the system Fe-Ni-S-C. However, while δC 13 variations within a meteorite may be discussed within this framework, little can be said as yet about possible causes for the suggested differences in C 13 concentrations between different meteorites.

The Redfields meteorite—A unique iron from Western Australia

SummaryA metallic mass brought to the Western Australian Museum from the Wongan Hills district N.W. of Perth has been identified as an iron meteorite of unique type. It has graphite inclusions about I mm across distributed throughout the metal giving a ‘raisin bread’ appearance. Its nickel content (6·65 %) is comparable with that of coarse octahedrites but the kamacite grain structure is anomalous. Its gallium, germanium, and nickel contents place it close to, but outside, Wasson's chemical group IIb. Taenite is absent and troilite is rare. Neumann bands in the kamacite are distorted and the kamacite has flowed around large schreibersite inclusions. The latter have an exceptionally low nickel content (7·0 %) and probably formed at an unusually high temperature. The kamacite contains more phosphorus than normal iron meteorites, and small schreibersite grains in the kamacite are relatively nickel-poor (22 %). The unusual structure of this iron is thought to be due to one or more of the factors high carbon, high phosphorus, and relatively rapid cooling.

THE GOSNELLS IRON — A FRAGMENT OF THE MOUNT DOOLING OCTAHEDRITE

A 1.5 kg iron found in 1960 at Gosnells, near Perth, Western Australia, belongs to Wasson's chemical group I‐An3 and is structurally unusual, being best described as a heat‐altered granular coarse octahedrite. It is chemically and structurally very similar to the Mount Dooling iron, found in 1909 about 400 km away, and has a fracture surface which fits the Mount Dooling mass very closely. The Gosnells fragment was probably transported by human agency, though it is not known when or by whom.