Diamond presolar

Presolar stardust grains diamond, graphite, carbides and oxides... 

Figure 5. Relative abundances of the Kr, Xe isotopes (Huss and Lewis 1994) in presolar diamonds have been measured in bulk samples (= many grains) and are plotted relative to solar wind abundances. The terrestrial atmosphere is shown for comparison and displays a pattern close to mass dependent fractionation relative to the solar wind. The primary nucleosynthetic processes at the origin of the different nuclei are also listed. Both Kr and Xe are elevated in the r-process isotopes, whereas only Xe is also enriched in the p-isotopes. These patterns are a strong argument in favor of a supernova origin for the diamonds. Ne isotopes in presolar diamond is within the field of bulk meteorite data.

Huss GR, Meshik AP, Smith JB, Hohenberg CM (2003) Presolar diamond, silicon carbide, and graphite in carbonaceous chondrites implications for thermal processing in the solar nebula. Geochim Cosmochim Acta 67 4823-4848... 

Nittler LR, Alexander CMOD (2003) Automated isotopic measurements of micron-sized dust application to meteoritic presolar silicon carbide. Geochim Cosmochim Acta 67 4961-4980 Nuth JA(1987) Small-particle physics and interstellar diamond. Nature 329 589... 

The discovery happened by accident. Lewis and Anders were frustrated by their failure to find the carrier of anomalous xenon in carbonaceous chondrites. They decided to try an extreme treatment to see if they could dissolve the carrier. They treated a sample of the colloidal fraction of an Allende residue with the harshest chemical oxidant known, hot perchloric acid. The black residue turned white, and to their surprise, when they measured it, the anomalous xenon was still there The residue consisted entirely of carbon, and when they performed electron diffraction measurements on it, they found that it consisted of tiny (nanometer sized) diamonds. After a detailed characterization that included chemical, structural, and isotopic studies, they reported the discovery of presolar diamond in early 1987 (Lewis et al., 1987). The 23-year search for the carrier of CCFXe (Xe-HL) was over, and the study of presolar grains had begun. 

The characteristics of the presolar diamonds also change with the metamorphic grade of the host meteorite. F igure 5.15 shows the typical bimodal release of heavy noble gases (here illustrated by xenon) in Orgueil, an unheated chondrite. This pattern is compared to the xenon-release patterns of two ordinary chondrites that have experienced different degrees of mild metamorphism. The amount of low-temperature gas, labeled P3 for historical reasons, is a sensitive function of temperature. Its abundance correlates well with other indicators of... 

Lewis, R. S., Tang, M., Wacker, J. F., Anders, E. and Steel, E. (1987) Interstellar diamonds in meteorites. Nature, 326, 160-162. The paper describing the discovery of the first presolar grains. 

Huss, G. R. and Lewis, R. S. (1994) Noble gases in presolar diamonds II Component abundances reflect thermal processing. Meteoritics, 28, 811-829. 

P3 and P6). Rather than being products of specific nucleosynthetic processes in specific stars, these components may represent mixtures of many stellar nucleosynthetic contributions, as might be found in the ISM (and our own solar system). It is worth recalling that presolar diamonds are too small to be analyzed separately, so the assortment of diamonds in a chondrite probably samples multiple stellar sources. 

C60 has not yet been detected in primitive meteorites, a finding that could demonstrate its existence in the early solar nebular or as a component of presolar dust. However, other allotropes of carbon, diamond and graphite, have been isolated from numerous chondritic samples. Studies of the isotopic composition and trace element content and these forms of carbon suggest that they condensed in circumstellar environments. Diamond may also have been produced in the early solar nebula and meteorite parent bodies by both low-temperature-low-pressure processes and shock events. Evidence for the occurrence of another carbon allotrope, with sp hybridized bonding, commonly known as carbyne, is presented. 

One of the enormous benefits of seeking diamond, or for that matter SiC, as presolar grain material is the incomparable resistance of the mineral to chemical attack. Other species are far more difficult but not impossible to isolate. 

Diamonds In bulk collections of large numbers of diamonds, 14N/15N near 400 is typical, confirming their presolar nature by the difference from the terrestrial ratio 272 (but see comments re. Jovian value, above and below). This isotopic ratio (as well as that of C) changes during stepwise combustion of the diamond collection, being much nearer to terrestrial 14N/15N = 272 in the earliest N released. The explanation is not known. 

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