Canyon Diablo Meteorite Research Articles

A metallographic study of some fragments of the canyon diablo meteorite

The microstructures of several specimens collected from the rim of Meteor Crater were studied by conventional metallographic techniques. The general metallographic features of these meteorite specimens are the result of shock metamorphism due to impact with the earth. Certain of the cohenite inclusions were observed (under polarized light) to be polycrystalline, with an apparently random grain orientation. Other cohenite particles were only partially recrystallized, and still others were monocrystalline. This recrystallization of monocrystalline cohenite is also attributed to shock metamorphism. The lowest temperature that these individual meteorites had previously experienced was studied by Knox's method. These particular specimens had apparently been exposed to temperatures between -60°C and -195°C. The results of this limited investigation illustrate that metallography is an extremely useful tool for the meteoriticist.

Hexagonal Diamond—A New Form of Carbon

A new crystalline form of carbon—hexagonal diamond—has been synthesized in the laboratory under conditions of static pressure exceeding about 130 kbar and temperature greater than about 1000°C. It is necessary to start with well-crystallized graphite in which the c axes of the crystallites are parallel to each other and to the direction of compression. There is electrical evidence that the transformation starts at room temperature but hexagonal diamond is not retrieved unless a setting temperature exceeding about 1000°C is applied. The electrical and crystal characteristics have been studied. The crystal structure is hexagonal with a=2.52 Å and c=4.12 Å. The theoretical density is 3.51+g/cm3, same as cubic diamond. It has also been prepared recently in another laboratory from crystalline graphite by a method involving intense shock compression and strong thermal quenching. More recently it has been discovered to be present to the extent of over 30% in the Canyon Diablo meteorite diamonds.

X-Ray diffraction analysis of cohenite from iron meteorites

It has recently been observed that cohenite grains from iron meteorites show evidence of shock-induced alterations in crystal character. This paper reports the results of an X-ray diffraction investigation of cohenite from 50 Canyon Diablo meteorites and 8 Odessa shock standards. The crystal character of cohenite appears rather sensitive to shock pressure over the range 0-> 1000 kb. The alterations observed apparently represent successive stages in the solid state recrystallization of cohenite. This recrystallization probably occurs during the high-pressure portion of the shock wave since, because of cohenite's thermodynamic instability, the rate of its graphitization during low-pressure annealing appears to be much more rapid than its rate of recrystallization. It has been found possible to establish a pressure scale based upon features observed in diffraction photographs of cohenite grains from shock standards. This pressure scale is qualitatively consistent with the metallographic shock criteria proposed previously. The pressure gradient deduced by microscopy in a particular specimen has been verified and was found to be 40 kb/cm. Estimates, from metallographic criteria, of the degree of shock suffered by Canyon Diablo meteorites is essentially paralleled by shock estimates based on cohenite alteration. The sensitivity of the X-ray technique also serves to identify shocked meteorites which have not been at a pressure high enough to induce metallographic changes.

Kamacite–Taenite Relationships in Iron Meteorites

A NUMBER of investigators1–3 have used the method of electron probe X-ray microanalysis in the examination of metallic meteorites. For those simple octahedrites which are free of visible thermal metamorphism there is general agreement that the various morphological forms of taenite are distinctly non-homogeneous with respect to nickel, whereas the bulk of the kamacite is of more uniform nickel content, although there is a decrease of nickel within the kamacite where it comes into contact with taenite1,3. Extensive measurements of this effect have been made by Agrell, Long and Ogilvie3 on a sample of the Canyon Diablo meteorite, for which they found a nickel content of 6.8 ± 0.2 per cent for the bulk kamacite as compared with about 5.7 at the interface. In the machine used by Agrell, Long and Ogilvie the X-rays could be collected in a direction lying in the plane which contained the normal to the specimen surface and the intersection of the kamacite–taenite boundary with the surface. This simple geometry minimizes the anomalous effects which can arise if X-rays generated in one phase are absorbed by passage through another phase.

The isotopic composition of silver in the Canyon Diablo meteorite

Trace quantities of silver in the iron meteorite Canyon Diablo were isolated by chemical procedures with an average yield of 80% The isotopic composition of 5 samples of silver from the meteorite was measured on a 12-inch radius of curvature, double-focusing, fast-sweep mass spectrometer. The isotopic composition of 18 samples of terrestrial silver was measured for comparison. The meteoritic and terrestrial ratios of Ag107/Ag109 were found to be identical to within 1%. The silver content of Canyon Diablo is 58 parts per billion from isotopic dilution analyses of aliquots of the meteorite samples. Blanks were less than 10% of the sample size in our analyses. We are thus unable to confirm a previous report of a 4% excess of Ag107 for Canyon Diablo.

Reply [to “Reply on ‘Origin of diamonds in the Canyon Diablo and Novo Urei meteorites’ by Neville L. Carter and George C. Kennedy”

Reply [to “Reply on ‘Origin of diamonds in the Canyon Diablo and Novo Urei meteorites’ by Neville L. Carter and George C. Kennedy”

Canyon Diablo meteorite: Metallographic and mass spectrometric study of 56 fragments

Canyon Diablo meteorite examined, using mass spectrometry and metallography, noting shock effects

Origin of diamonds in the Canyon Diablo and Novo Urei meteorites

Detailed optical studies of the textural features of several hundred diamonds and associated phases in three specimens of the Canyon Diablo meteorite and one specimen of the Novo Urei achondrite were made. Diamonds in the Canyon Diablo are associated exclusively with troilite, graphite, and schreibersite, and they occur both in shock-heated and unreheated specimens. Diamonds in the Novo Urei occur in pods and lenses interstitial to slightly deformed olivine and pyroxene crystals. The diamonds, once formed, were shattered and partially graphitized. X-ray and electron microscope studies show that the diamond bodies, which range in size up to 2 mm in Canyon Diablo, are now composed of 0.5-μ subindividuals with nearly random orientations. The evidence obtained from these studies indicates that the diamonds probably precipitated as a stable phase from a late-freezing residuum composed primarily of iron sulfide, iron phosphide, and carbon, under high gravitational pressures. The diamonds were subsequently shattered, distorted, and partially graphitized, possibly from a pressure drop due to the disruption of the large parent body. The physical evidence against the theory that the diamonds originated by high temperature and pressures due to shock is convincing.

Sputtering of meteorites by He+, Ne+, and Ar+ ions

This letter gives some measurements on the erosion of meteorites by He+ and Ne+ ions. The experiments were performed in the isotope separator of the Laboratory for Mass Separation as described in a previous article on sputtering by Ar+ ions [Heymann and Fluit, 1962], The He+ sputtering coefficient for the Canyon Diablo meteorite has been measured by a technique different from that described previously because the removed material was too small to be measured by weighing. In this technique, the meteorite was irradiated with slow neutrons in the Argonaut reactor of the Reactor Centrum Nederland, Petten. The irradiated target was mounted inside a glass sphere at an angle of 45° to the separator ion beam, which entered the sphere through a circular hole (Figure 1). The sputtered material was deposited on the inside of the sphere. A small fraction (<10 per cent) was lost through the entry hole. The sputtered material was dissolved in acid containing cobalt, iron, and nickel carriers. The cobalt was isolated with an anion-exchange resin and electroplated on platinum disks, and the Co60 activity was measured in a proportional counter of low background.

The isotopic composition of silver in iron meteorites

Microgram quantities of silver were extracted from the troilite of Toluca iron meteorite and the metal phases of Sikhote Alin and Canyon Diablo meteorites using anion-exchange techniques. Isotopic analysis of silver in iron meteorites indicates a 2–3 per cent higher Ag 107 Ag 109 ratio relative to the terrestrial silver. If this excess Ag 107 is attributed to the decay of the extinct radioactive nuclide Pd 107, an unreasonably short interval of time between the end of nucleosynthesis and the formation of iron meteorites is indicated. The silver isotopic anomaly in iron meteorites appears too large to be attributed entirely to Pd 107 produced in the galactic synthesis of elements, and may have to be interpreted in terms of a last-minute contribution of some amounts of short-lived radioactivities to the solar nebula, or by postulating that some Pd 107 was produced in the solar system in its early stages, after its separation from the galactic nucleosynthesis. In either case, other short-lived radioactive nuclides would be extant in the early history of the solar nebula, and extinct radioactivity as the heat source in the early history of meteorite parent bodies becomes a definite possibility.

Structure and composition of Canyon Diablo meteorites as related to zonal distribution of fragments.

Structure and composition of Canyon Diablo meteorites as related to zonal distribution of fragments.