Metal Globules Research Articles

Heterogenity of planetesimal collisional plume probed by glass inclusions in metal globules of Sierra Gorda 013, an unusual CBa‐like chondrite

AbstractMetal‐rich carbonaceous CB chondrites are generally assumed to be materials accreted from the gas–dust plume formed in catastrophic collisions of planetesimals, at least one of which was differentiated into a metal core and silicate shell. Micron‐sized inclusions of siliceous alkali‐rich glasses associated with sulfides were found in the metal globules of the Sierra Gorda 013 (SG 013), a CBa‐like chondrite. These inclusions are unusual carriers of volatile alkalis which are commonly depleted in CB chondrites. The inclusions are presented by two types: (1) Al‐bearing Nb‐poor glass associated with daubréelite and (2) Nb‐bearing Ca,Al,Mg‐poor glass associated with an unknown Na‐bearing Cr‐sulfide. The glass compositions do not correspond to equilibrium condensation, evaporation, or melting. The Nb‐bearing glass has a superchondritic Nb/Ta ratio (31) most likely indicating the fractionation of Nb and Ta in the high‐temperature gas–dust impact plume due to condensation from vapor or evaporation of precursor Nb‐rich particles. The glasses are interpreted as reaction products between refractory plume condensate particles (or possibly planetary or chondritic solids) with relatively low‐temperature K‐Na‐Si‐rich gas in oxidized conditions, possibly in a common plume vapor reservoir. Compositional differences indicate that the glasses and sulfides originated from several different sources under different fO2, fS2, andTconditions and were likely combined together and transported to the metal globule formation region by material flows in the heterogeneous impact plume. The glass–sulfide particles were enclosed in the globules aggregated from smaller solid or molten metal grains. The metal globules were further melted during transport to the high‐temperature plume region or by plume shockwave heating. Thus, the composition of the glasses, the host metal, and the main mass of SG 013 shows dynamic heterogeneity of physical conditions and impact plume composition after a large‐scale planetesimal collision.

Sierra Gorda 013: Unusual CBa‐like chondrite

AbstractThe new metal‐enriched anomalous chondrite Sierra Gorda 013 (SG 013) contains two different lithologies. Lithology 1 (L1) is represented by anomalous CBa‐like chondrite material containing ~80 vol% of Fe,Ni‐metal particles and globules up to 6 mm in size; chondrules and clasts of types POP, BO, and SO (up to 5 mm in diameter); rare sulfides; and shock melted silicate–metal areas. It does not contain any fine‐grained matrix. Several chondrules contain chromite–pyroxene symplectites. Lithology 2 (L2) has a recrystallized texture with evenly distributed olivine, pyroxene and plagioclase. L2 does not have any chondrules or sulfides, and contains less Fe,Ni‐ metal (~25 vol%) than L1. Both lithologies contain reduced olivine (Fa2–4) and pyroxene (Fs3.5), similar to CBa chondrites. Similar to CBa, there is no Ni‐Co correlation in the SG 013 metal. Rare sulfides in L1 are enriched in V. Chromite was observed in both lithologies. Oxygen isotope compositions of both lithologies are different but in the range of CBa chondrites. Bulk major and trace element geochemistry of nonporphyritic chondrules and bulk siderophile compositions in metal globules of L1 indicate elemental fractionation during formation of metallic and silicate objects with records of the evaporation process: depletion in moderate and volatile elements with the exception of Cr. Bulk geochemistry of porphyritic chondrules of L1 and the silicate portion of L2 is similar and also indicates evaporation processes. The rare Earth element (REE) distribution of L1 chondrules records a very fractionated signature corresponding to possible differentiated precursor material, while the REE pattern of L2 is primitive chondritic. The formation of SG 013 could be explained by collisions of planetesimals producing an impact plume, the precursor material of which could be chondritic and possibly differentiated. Both lithologies were affected by secondary processes: L1 preserved the traces of shock events and partial melting resulting in formation of symplectites in chondrules, melt pockets, and metal–silicate melt between the metal globules; L2 was affected by shock thermal metamorphism (up to 900 °C) resulting in recrystallization.

IIE irons: Origin, relationship to ordinary chondrites, and evidence for siderophile‐element fractionations caused by chondrule formation

AbstractIIE irons were derived from chondritic precursors that were the most reduced ordinary chondrites. The bulk chemical (e.g., Ir/Ni, Ir/Au, Au/Ni, Co/Ni) and bulk isotopic (i.e., Δ17O and δ74/70Ge) compositions of IIE irons lie along extensions of LL‐L‐H trends. Chondrule‐bearing silicate clasts in IIE irons have mineralogical and petrological characteristics that extend LL‐L‐H trends; these clasts have higher modal metallic Fe‐Ni and lower values for olivine Fa, low‐Ca‐pyroxene Fs, kamacite Co, and mean chondrule diameter. IIE irons are modeled as agglomerating before H‐L‐LL chondrites; they acquired more 26Al and reached the Fe,Ni‐FeS eutectic temperature (~940 °C). An FeS‐rich metallic melt separated from unmelted silicate and drained to the core, eventually generating a dynamo. Most IIE metal remained within the crust/mantle region alongside recrystallized chondritic clasts. Alkali‐rich IIE silicate inclusions formed from late‐stage impacts via preferential melting of plagioclase. Some separation of K from Na occurred during vapor transport. Because most type I chondrules formed before most type II chondrules, the (type I)/(type II) modal ratio decreased from IIE to H to L to LL during agglomeration. Earlier‐formed chondrules acquired higher abundances of refractory metal nuggets within CAI‐fragment precursors, accounting for systematic changes in bulk OC of refractory/common siderophile and refractory/volatile siderophile ratios (IIE>H>L>LL). Because more Au and Co than Ni were retained in silicates, loss of metal globules from spinning partly molten type I chondrules caused systematic whole‐rock decreases in Au/Ni and Co/Ni from IIE through LL. Expelled globules had different nebular aerodynamic properties than chondrules and drifted away (accounting, in part, for the metal/silicate fractionation).

Laser Polishing of Ti6Al4V Fabricated by Selective Laser Melting

Selective laser melting (SLM) is emerging as a promising 3D printing method for orthopedic and dental applications. However, SLM-based Ti6Al4V components frequently exhibit high roughness values and partial surface defects. Laser polishing (LP) is a newly developed technology to improve the surface quality of metals. In this research, LP is applied to improve the surface finish of components. The results show that the laser beam can neatly ablate the aggregates of metallic globules and repair cracks and pores on the surface, resulting in a smooth surface with nanocomposites. Overall, the results indicate that using LP optimizes surface morphology to favor fatigue behavior and osteoblastic differentiation. These findings provide foundational data to improve the surface roughness of a laser-polished implant and pave the way for optimized mechanical behavior and biocompatibility via the laser process.

Quenched primary melt in Ramlat as Sahmah 517 – Snapshot of ureilite anatexis in the early solar system

Ureilites are the second largest group of achondrite meteorites but consensus is still lacking on the nature of their precursors, melting processes, and the genetic relationship between monomict ureilites and brecciated ureilites. The recently found ureilite Ramlat as Sahmah 517 is of special interest in this context. This meteorite lacks shock features in its primary silicates and belongs to a rare augite- and chromite-bearing subset of the monomict ferroan ureilites. It hosts abundant intergranular glass veinlets speckled with pyroxene and metal globules. Detailed petrographic investigations show that the Si-Al-rich glass represents quenched anatectic melt that was present prior to formation of the reduced olivine rims by incomplete low-pressure equilibration (smelting) of carbon and silicates. The melt facilitated smelting which, along with rapid crystallization of secondary pyroxene, modified the originally trachyandesitic melt. Melt-silicate equilibrium preceding these events is constrained by modelling using MELTS and the first reported in-situ measurements of LREE-enriched glass that is largely complementary to the depleted mafic silicates in monomict ureilites. The inferred major element composition of the partial melt that formed in RaS 517 is similar to that of trachyandesite in Almahata Sitta but RaS 517 lacks phosphates which are abundant in the Almahata Sitta trachyandesite and in alkali-rich feldspathic clasts in polymict ureilites. The LREE-depletion in the dominant monomict ferroan ureilite population can be explained by the formation of melt fractions similar to the glass in RaS 517 after initial rapid melting of phosphates. These finds provide evidence for a genetic relationship between ferroan ureilites and lithologies similar to the Almahata Sitta trachyandesite and further suggest that these ureilites formed by partial melting of P- and alkali-rich precursors with trace element concentrations similar to equilibrated ordinary chondrites. Quenched Si-Al-rich glass also occurs in magnesian ureilites but has lower concentrations of alkalis and LREE-depleted trace element signatures which can reflect more depleted compositions at the onset of partial melting. The evidence presented here favors a scenario in which the primary ureilite differentiation was driven by gradual heating from radioactive decay with resulting temperatures (>1100 °C) being maintained until disruption of the ureilite parent asteroid.

Trinitite redux: Mineralogy and petrology

Trinitite is the glass formed during the first atomic bomb test near Socorro, New Mexico, on July 16, 1945. The protolith for the glass is arkosic sand. The majority of the glass is bottle green in color, but a red variety is found in the northern quadrant of the test site. Glass beads and dumbbells, similar in morphology to micro-tektites, are also found at the Trinity site. The original description of this material, which appeared in American Mineralogist in 1948, noted the presence of two glasses with distinctly different indices of refraction (n = 1.46 and 1.51–1.54). Scanning electron microscopy (SEM) and Quantitative Evaluation of Minerals by SCANning electron microscopy (QEMSCAN) analysis is used to investigate the chemical composition and fine-scale structure of the glass. The glass is heterogeneous at the tens of micrometer scale with discrete layers of glass showing flow-like structures. The low index of refraction glass is essentially SiO2 (high-Si glass), but the higher index of refraction glass (low-Si glass) shows a range of chemical compositions. Embedded in the glass are partially melted quartz (α-quartz as determined by X-ray diffraction) and feldspar grains. The red trinitite consists of the same two glass components along with additional Cu-rich, Fe-rich, and Pb-rich silicate glasses. Metallic globules are common in the red trinitite In terms of viscosity, the high-Si and low-Si glasses differ by several orders of magnitude, and there is minimal mixing between the two glasses. QEMSCAN analysis reveals that there are several chemical subgroups (that can be characterized as simple mixtures of melted mineral components) within the low-Si glasses, and there is limited mixing between these glass subgroups. The red trinitite contains regions of Fe-rich glass, which show sharp contact with surrounding Fe-poor glass. Both the textural and chemical data suggest that these two glasses existed as immiscible liquids. The metallic droplets in the red trinitite, which consist of variable amounts of Cu, Pb, and Fe, show textural evidence of unmixing. These metals are largely derived from anthropogenic sources—Cu wire, Pb bricks, and the steel tower and bomb casing. The combination of mineralogical and chemical data indicate that temperatures on the order of 1600 °C and pressures of at least 8 GPa were reached during the atomic detonation and that there was a reducing environment during cooling, as evidenced by the presence of native metals, metal sulfides, and a low-Fe3+/Fe2+ ratio. Independent estimates of maximum temperature during the detonation are on the order of 8000 K, far higher than suggested by the mineral data. This discrepancy is probably due to the very short duration of the event. In all respects, the trinitite glasses are similar to tektites and fulgurites, and by analogy one conclusion is that temperature estimates based on mineralogical observations for these materials also underestimate the maximum temperatures.

Martian Dunite NWA 2737: Petrographic constraints on geological history, shock events, and olivine color

Meteorite Northwest Africa (NWA) 2737 is the second known chassignite, an olivine‐rich igneous rock with mineral compositions and isotopic ratios that suggest it formed on Mars. NWA 2737 consists of ∼85% vol. olivine (Mg#, molar Mg/(Mg + Fe), of 78.3 ± 0.4%), which is notable because it is black in hand sample and brown in thin section. Other minerals include chromite, pyroxenes (augite, pigeonite, orthopyroxene), and diaplectic glass of alkali‐feldspar composition. Aqueous alteration is minimal and appears only as slight dissolution of glass. NWA 2737 formed by accumulation of olivine and chromite from a basaltic magma; the other minerals represent magma trapped among the cumulus grains. Minerals are compositionally homogeneous, consistent with chemical equilibration in late and postigneous cooling. Two‐pyroxene thermometry gives equilibration temperatures ∼1150°C, implying a significant time spent at the basalt solidus. Olivine‐spinel‐pyroxene equilibria give ∼825°C (possibly the T of mesostasis crystallization) at an oxidation state of ∼QMF‐1. This oxidation state is consistent with low Fe3+ in olivine (determined by EMP, Mössbauer spectra, and synchrotron micro‐XANES spectroscopy) and with ∼10% of the iron in pyroxene being Fe3+. NWA 2737 experienced two shock events. The first shock, to stage S5–S6, affected the olivine by producing in it planar deformation features, intense mosaicism and lattice strain, and abundant droplets of iron‐nickel metal, 5–15 nm in diameter. At this stage the olivine became deeply colored, i.e., strongly absorbing at visible and near‐infrared (NIR) wavelengths. This shock event and its thermal pulse probably occurred at ∼170 Ma, the Ar‐Ar age of NWA 2737. The colored olivine is cut by ribbons of coarser, uncolored olivine with long axes along [100] and shorter axes on {021} planes: These are consistent with the easy slip law for olivine [100]{021}, which is activated at moderate strain rate at high temperature. Within these ribbons the olivine was coarsened and the iron metal globules coalesced to micron‐sized grains. The ribbons also are mosaicized and cut by planar fractures, which bespeak a second shock event, possibly that of ejection from Mars. The deeply colored olivine in NWA 2737 is unusual and represents a new “ground truth” type for remote sensing of Mars. Understanding the occurrence of the brown color in olivine in NWA 2737 places important constraints on interpretation of optical measurements.

Formation of metal and silicate globules in Gujba: a new Bencubbin-like meteorite fall

Gujba is a coarse-grained meteorite fall composed of 41 vol% large kamacite globules, 20 vol% large light-colored silicate globules with cryptocrystalline, barred pyroxene and barred olivine textures, 39 vol% dark-colored, silicate-rich matrix, and rare refractory inclusions. Gujba resembles Bencubbin and Weatherford in texture, oxygen-isotopic composition and in having high bulk δ 15N values (∼+685‰). The 3He cosmic-ray exposure age of Gujba (26 ± 7 Ma) is essentially identical to that of Bencubbin, suggesting that they were both reduced to meter-size fragments in the same parent-body collision. The Gujba metal globules exhibit metal-troilite quench textures and vary in their abundances of troilite and volatile siderophile elements. We suggest that the metal globules formed as liquid droplets either via condensation in an impact-generated vapor plume or by evaporation of preexisting metal particles in a plume. The lower the abundance of volatile elements in the metal globules, the higher the globule quench temperature. We infer that the large silicate globules also formed from completely molten droplets; their low volatile-element abundances indicate that they also formed at high temperatures, probably by processes analogous to those that formed the metal globules. The coarse-grained Bencubbin-Weatherford-Gujba meteorites may represent a depositional component from the vapor cloud enriched in coarse and dense particles. A second class of Bencubbin-like meteorites (represented by Hammadah al Hamra 237 and QUE 94411) may be a finer fraction derived from the same vapor cloud.

Formation of mesosiderites by fragmentation and reaccretion of a large differentiated asteroid

Abstract—We propose that mesosiderites formed when a 200–400 km diameter asteroid with a molten core was disrupted by a 50–150 km diameter projectile. To test whether impacts can excavate core iron and mix it with crustal material, we used a low‐resolution, smoothed‐particle hydrodynamics computer simulation. For 50–300 km diameter differentiated targets, we found that significant proportions of scrambled core material (and hence potential mesosiderite metal material) could be generated. For near‐catastrophic impacts that reduce the target to 80% of its original diameter and about half of its original mass, the proportion of scrambled core material would be about 5 vol%, equivalent to ∼10 vol% of mesosiderite‐like material. The paucity of olivine in mesosiderites and the lack of metal‐poor or troilite‐rich meteorites from the mesosiderite body probably reflect biased sampling. Mesosiderites may be olivine‐poor because mantle material was preferentially excluded from the metal‐rich regions of the reaccreted body. Molten metal globules probably crystallized around small, cool fragments of crust hindering migration of metal to the core. If mantle fragments were much hotter and larger than crustal fragments, little metal would have crystallized around the mantle fragments allowing olivine and molten metal to separate gravitationally. The rapid cooling rates of mesosiderites above 850 °C can be attributed to local thermal equilibration between hot and cold ejecta. Very slow cooling below 400 °C probably reflects the large size of the body and the excellent thermal insulation provided by the reaccreted debris. We infer that our model is more plausible than an earlier model that invoked an impact at ∼1 km/s to mix projectile metal with target silicates. If large impacts cannot effectively strip mantles from asteroidal cores, as we infer, we should expect few large eroded asteroids to have surfaces composed purely of mantle or core material. This may help to explain why relatively few olivine‐rich (A‐type) and metal‐rich asteroids (M‐type) are known. Some S‐type asteroids may be scrambled differentiated bodies.

Iridium distributions in silicate glass for sedimentology studies

Iridium distributions in silicate glass for sedimentology studies

Cutaneous reaction from a broken thermometer

A cutaneous and soft tissue reaction that resulted from a broken thermometer inside the mouth of a 10-year-old boy is described. Metallic mercury globules and glass pieces were identified in the excised tissue. On histologic examination, a zone of necrosis, polymorphonuclear leukocytes, macrophages, and multinucleated giant cells surrounded metallic mercury that appeared as dark opaque globules. Dense fibrosis and reactive lymphoid hyperplasia were also noted in the dermis and deeper tissues. The gold lysis test, scanning electron microscopy, and energy-dispersive x-ray analysis confirmed the presence of mercury in the tissue. A literature review on cutaneous mercury granuloma illustrates its unpredictable course. The cutaneous reaction may remain localized, but some cases are associated with an elevated mercury level in blood and urine, pulmonary embolism, mercury poisoning, and even with fatal outcome. Various manifestations of mercury poisoning and guidelines for the management of cutaneous mercury granuloma are discussed.

Lightning Strike Fusion: Extreme Reduction and Metal-Silicate Liquid Immiscibility

A glassy fulgurite, formed recently on a morainal ridge in southeastern Michigan, contains micrometer- to centimeter-sized metallic globules rich in native silicon, which unmixed from a silica-rich liquid. The unusual character of these globules and their potential for elucidating conditions of fulgurite formation prompted further study. Thermodynamic calculations indicate that temperatures in excess of 2000 K and reducing conditions approaching those of the SiO(2)-Si buffer were needed to form the coexisting metallic and silicate liquids. The phases produced are among the most highly reduced naturally occurring materials known. Some occurrences of other highly reduced minerals may also be due to lightning strike reduction. Extreme reduction and volatilization may also occur during high-temperature events such as lightning strikes in presolar nebulae and impacts of extraterrestrial bodies. As a result of scavenging of platinum-group elements by highly reduced metallic liquids, geochemical anomalies associated with the Cretaceous-Tertiary boundary may have a significant terrestrial component even if produced through bolide impact.

Cosmic spherules, asteroidal collisions and the possibility of detecting changes in the solar constant

Summary. The Poynting–Robertson effect, applied to ‘iron’spherules in dated deep-sea cores, should provide a test of whether or not cosmic spherules originate in asteroidal collisions. If D is the overall diameter of the spherule and δ its bulk density, the effect predicts that a number of straight sloping lines should appear in a plot of Dδ against arrival time for spherules down a core. From a Pacific core, 223 iron spherules (D≥ 45 μm), in a variety of states, were examined to estimate δ. But, a decision was made to use only 100 spherules in a final Dδ plot as δ had dubious accuracy for spherules with rusted or missing metal globules and for those with enclosed or burst bubbies. In this plot, two parallel sloping lines appear with some clarity. They are widely spaced in time and could be due to infrequent collisions amongst the few asteroids at ∼ 3.4 au. Possibly, there are more frequent collisions in the main belts, but lines showing these are not clearly revealed. During the examination (i.e. by cracking the spherules), 16 iron spherules of a new type were found. Instead of a metal globule, a black bead of glass is eccentrically enclosed in the oxide shell. The bead is a true non-magnetic glass, ruby-red in thin section. It is rich in oxides of Fe, Ni and Si. The metal globules from 59 spherules were analysed for Ni. This allowed the Ni percentage to be estimated for the original metal, prior to its partial oxidation. This Ni distribution is similar to the distribution in meteoritic iron. If an asteroidal origin is correct, it follows, from mass influx estimations, that an appreciable fraction of spherules must exist in the zodiacal cloud. Catastrophic asteroidal collision is suggested in order to produce a copious supply of melt-ejecta by frictional heating. It is also presumed that meteoritic chondrules were large droplets formed in ancient catastrophic asteroidal collisions. To detect changes in the Sun's luminosity, very accurate plotting is required. It is shown that the errors of the method are too great to detect any possible changes during the glacial cycles. However, long-period oscillations or a steady trend over ∼ 1 Myr are within range of the method for changes ∼ 3 per cent of the mean Sun.

Preparation and properties of iron-boron metallic glass ribbons melt spun in air

The preparation of metallic glass ribbons by melt spinning is a simple technique; however, a researcher often faces many problems when undertaking the preparation of such ribbons. The difficulties encountered are oxidation of the melt, choking of the nozzle by the solidified metal, formation of metal globules or ribbon fragments, oxidation of the ribbons, etc. These problems are particularly severe when working with high melting point alloys. This report describes certain experimental techniques used to overcome problems in preparation of metallic glass ribbons of iron-boron and other high melting point alloys. The ribbons thus produced have been characterized by transmission electron microscopy, mechanical tests and differential thermal analysis. The mechanical strength of the ribbon is comparable to the best recorded strength for ribbons of similar composition. Thedta data support the view that the formation of the phase Fe23B6 takes place upon crystallization of the eutectic alloy.

Multiple metallic mercury emboli

Metallic mercury embolisation is an unusual entity. It can be deliberate or accidental, arterial or venous. The radiological detection of the metallic mercury globules, and the pattern of distribution within the body, provide valuable information as to the mode of entry, especially when this is not forthcoming from the patient. In the chest, the distinction between pulmonary intravascular mercury emboli from aspirated intra-bronchial mercury is difficult. Points of differentiation are outlined, with special reference to the value of Ventilation and Perfusion (V/Q) radionuclide scans carried out in this case of self-administered intravenous metallic mercury embolisation. An unmarried 27-year-old female nurse presented on 2.4.84 with a week's history of a pyrexial illness, right pleuritic chest pain and marked repeated haemoptysis. Reduced air entry and a dull percussion note were elicited in the right lung base. There was no evidence of a deep venous thrombosis nor was the patient taking the contraceptive ...

Cosmic Spherules, Asteroid Collisions and the Solar Constant

AbstractIn 1980 (Phil. Trans. Roy. Soc. 297, 495) and in 1983 (Geophys. Jour. Roy. Astr. Soc. 75, 473) it was proposed that cosmic spherules are formed as splash ejecta in asteroidal collisions. The Poynting-Robertson effect size-sorts the spherules as they spiral to Earth in circular orbits. The time taken in My is given byΔt = 3.5 × 10−7 Dδ (a2 − 1)where a (in AU) is the collision distance from the Sun, D (in um) is the diameter of the spherules and δ (in kg/m−3) its density. In the 1983 paper, we tested the hypothesis by plotting the size of all the iron spherules (≥ 43 μm diam.) against time for two dated N. Pacific cores. Sloping lines, giving a ~ 2.1 AU, could be discerned; but their existence could be disputed - see figure 6.In current work, all the spherules from core V21-65 have been cracked open to find δ. Out of 220 spherules, 65 have rusted metal globules and these (Dδ) points give a confused plot, because of inaccurate δ-values. However, 66 spherules have their metal globules well preserved. Since globule diameter and %Ni can be accurately measured, δ can be calculated. These (Dδ) points show two sloping lines with some clarity, giving a ~ 3.4 AU; also, there are vague lines, giving a-values well within the main asteroid belt.To establish the hypothesis, wide cores are needed, giving an abundance of undamaged spherules. To obtain accurate a-values, the Robertson formula requires correction because of the spherule’s “hummocky” oxide surface. Also, any waviness in the sloping lines could be a measure of a variable solar constant.A new kind of iron spherule was found because of the cracking; 13 enclose opaque beads of true glass (rich in Fe, Ni and Si, no Mg) instead of metal globules. Crushed bits are deep ruby-red and nonmagnetic.

Metallography and thermal history of the Tieschitz unequilibrated meteorite — Metallic chondrules and the origin of polycrystalline taenite

It has been an enigma that in the Tieschitz, H3, and other unequilibrated chondrites the silicates show quench textures yet their metallic minerals, according to the Wood [6] model, appear to have cooled extremely slowly.In Tieschitz, spherical metallic chondrules up to 500 μm in diameter, with textures indicating an origin as liquid droplets, consist of polycrystalline intergrowths of α(kamacite), γ(taenite) and troilite. Interface Ni compositions of contiguous α (∼5 wt.%) and γ (∼50 wt.%) grains define equilibrium tie-line relationships in the Fe-Ni system indicating equilibration to ∼350°C (620 K). Polycrystalline γ(taenite) is multi-zoned with respect to Ni and is interpreted as the relict of a primary solidification structure. A mechanism whereby Ni compositional heterogeneities were produced in γ(taenite) by the rapid, non-equilibrium cooling of FeNiS melts during chondrule formation is discussed.Comparisons with lunar metal globules indicate solidification rates for Tieschitz metallic chondrules in the range 1–106 K/s. It is suggested that before or during aggregation, sub-solidus cooling in the temperature range ∼700–1400°C with cooling times of days to weeks allowed the preservation of a relict solidification structure in metallic chondrules. At a temperature of ∼700°C accretion and shallow burial (1–10 m) on the surface of the Tieschitz parent body provided insulation with slower cooling required to nucleate and grow α(kamacite) from the heterogeneous γ(taenite) under equilibrium conditions by the process of solid state diffusion proposed by Wood [6]. The cooling rate (1 K/106 yr) through 500°C derived using the Wood model is shown to be an underestimate of the real cooling rate of Tieschitz metal through that temperature, since it does not take into account Ni heterogeneities produced at higher temperatures. A rough estimate of the post-accretional cooling rate is obtained from the average size of α(kamacite) grains(<100 μm) andTeqα ∼ 350°C indicating a cooling rate of the order of<1K/103yr through 500°C.

The grape cluster, metal particle 63344,1

Metal particle 63344,1 consists of hundreds of metallic globules welded together to form a structure somewhat like a bunch of grapes. It is the largest lunar metal sample found to date, over 5 mm in its longest dimension. Silicate material is attached to the outside of the sample and consists mainly of glass and fragments of An-rich plagioclase derived from a regolith composed of fragments of highland-type rocks. The globules are all of the same composition (6.25 wt.% Ni, 0.35 wt.% Co, 0.8 wt.% P and Fe) and were produced at the same time and from the same source. No primary solidification structure was observed in the globules. A Widmansta¨tten pattern of kamacite in taenite and a precipitation pattern of phosphides, which were equilibrated to a temperature of ⪯600°C, also developed in the metal. The metallographic evidence indicates that the particle was slow cooled from the solidification temperature (∼1300°C) taking days to possibly months to reach 600°C. Two possible mechanisms are proposed for the formation of the globules of 63344,1. One mechanism involves the primary impact of an iron meteorite which produces a metallic liquid and vapor phase. The second mechanism involves the formation of a liquid pool of metal after impact of an iron meteorite projectile followed by a secondary impact in the liquid metal pool. Both mechanisms call for special conditions and sequences of events in order to form a chemically coherent cluster of metal globules uncontaminated by silicates. These globules may adhere after partial solidification and the particle may be slow cooled by burial 0.5–5 m deep in the original ejecta blanket.

A Classification for Granulation in Ancient Metalwork

Granulation, long considered to have been made by a unique process, decorates some of the most spectacular monuments of the ancient goldsmithjeweler. Pieces such as the great fibula from the Regolini-Galassi Tomb, 31.5 centimeters high, and heavily ornamented with quantities of minute, metal globules,' have made Etruscan jewelry and its most typical decoration-granulation-well known to all who admire fine metalwork. The ornamentation looks as though it would be difficult to do. Problems connected with the making of granulation were called to public attention over a hundred years ago by Alessandro Castellani,2 a professional jeweler who wrote and lectured extensively on the techniques used in ancient jewelry. In the wake of Castellani's revelations came countless speculations about this lost art. The belief spread that all granulation owed its construction to a single process, once lost, but recently found.3 Early in the course of this study it became apparent that a one-process theory was not supported by the evidence. Differences in the grainwork on objects from different sources were noted. What gave every appearance of, not one, but sever l types of granulation were detected, including a number of kinds of decoration that produced th superficial effect of granulation. The variations observed concern certain features

Shock induced thermal metamorphism and mechanical deformations in the Ramsdorf chondrite

The grey hypersthene chondrite Ramsdorf—which has short and concordant 4He-U/Th- and 40Ar- 40K-gas retention ages—shows unambiguous evidence for severe thermal and mechanical alterations. 1. (1) The distribution of metal and troilite is very inhomogeneous. Both are found together in rather large, millimeter-sized patches near slickenside “veins”. 2. (2) The normal separation of the metal into individual grains of Ni-poor kamacite and Ni-rich taenite is lacking. Instead, it occurs as rounded globules ( d ≲ 1 mm) with an interior Ni-content of about 11 per cent and a Ni-rich rim. We believe these rims not to be due to solid state lattice diffusion but to crystallization of metal from the melt. 3. (3) The silicate portion is extensively “recrystallized”: only occasionally chondrule remnants can be discovered; the feldspar (12 per cent An) has been transformed into a clear isotropic glass, which must have been a liquid melt proper. 4. (4) The pyroxenes are clinopyroxenes and are high (up to 16·3 per cent) and variable in CaO, the highest values being found at the pyroxene-glass interfaces. In about 30 per cent of all cases the CaO-content falls into the immiscibility gap of the enstatite-ferrosilite-diopside-hedenbergite system. 5. (5) Chromite occurs as small euhedral crystals in the glassy silicate matrix and as larger badly “corroded” crystals at the silicate-troilite boundaries. 6. (6) Some pyroxene crystals have been broken and the fragments displaced over short distances. In some metal globules shearing forces have shifted portions of the globules over distances up to 300 microns. At these shearing planes the Ni-rich rim is missing indicating the mechanical deformation to be a late feature acquired after the thermal alterations. It is proposed that the observed features came about by the following sequence of events: Shock heating with a mean residual temperature of about 1200°C, homogenization and redistribution of a metal + troilite melt by acceleration forces, rapid cooling to about 900°C within less than one month, a secondary collision causing the mechanical deformations. The rapid cooling indicates Ramsdorf to have had a radius of less than 2 m—more probably less than about 30 cm—at that time. At present it cannot be decided unambiguously whether this sequence of events occured 4 Ma ago-the cosmic ray exposure age-or 400 Ma ago—the radiogenic gas retention age.