Natural occurrence of silicon carbide in a diamondiferous kimberlite from Fuxian

Leung, I. S.; Guo, Wenxiang; Friedman, Irving; Gleason, Jim D.

doi:10.1038/346352a0

Cited by 71 publications

(28 citation statements)

References 9 publications

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“…Even in the highly oxidized environment of the Earth's crust, silicon carbide can be found as a bona fide mineral (Leung et al, 1990), where it may be the result of metamorphic reprocessing of silicate under highly reducing conditions (Mathez et al, 1995). Silicon carbide is also a widely distributed component of carbonrich grains in carbonaceous chondrites (Bernatowicz et al, 2003), as is silicon nitride (Pillinger, 1992).…”

Section: Organosilanes In Astronomical Contextmentioning

confidence: 98%

Many Chemistries Could Be Used to Build Living Systems

2004

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It has been widely suggested that life based around carbon, hydrogen, oxygen, and nitrogen is the only plausible biochemistry, and specifically that terrestrial biochemistry of nucleic acids, proteins, and sugars is likely to be "universal." This is not an inevitable conclusion from our knowledge of chemistry. I argue that it is the nature of the liquid in which life evolves that defines the most appropriate chemistry. Fluids other than water could be abundant on a cosmic scale and could therefore be an environment in which non-terrestrial biochemistry could evolve. The chemical nature of these liquids could lead to quite different biochemistries, a hypothesis discussed in the context of the proposed "ammonochemistry" of the internal oceans of the Galilean satellites and a more speculative "silicon biochemistry" in liquid nitrogen. These different chemistries satisfy the thermodynamic drive for life through different mechanisms, and so will have different chemical signatures than terrestrial biochemistry.

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Section: Organosilanes In Astronomical Contextmentioning

confidence: 98%

Many Chemistries Could Be Used to Build Living Systems

2004

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“…The reason for such enthusiasm surrounding natural SiC is that, like diamond and graphite, SiC may be an important C-bearing phase in the Earthʼs mantle. It may provide information about carbon cycling (Leung 1990;Leung et al 1990) and redox condition, which in turn affects the volatiles composition in deep Earth, the occurrence of partial melting, and the geochemistry of chalcophile and siderophile elements (Mathez et al 1995 and references therein).…”

Section: Introductionmentioning

confidence: 98%

The 6H-SiC structure model: Further refinement from SCXRD data from a terrestrial moissanite

Capitani

Pierro

Tempesta

2007

American Mineralogist

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The crystal structure of a terrestrial 6H-SiC moissanite has been reÞ ned in the P6 3 mc S.G. from area detector single crystal X-ray data, down to an R-index on the observed reß ections of 0.0205. The cell parameters reÞ ned over all the collected reß ections are a = 3.0810(2) and c = 15.1248(10) Å. The average Si-C bond lengths are 1.8898 Å, with average bonds along the stacking direction (1.8993 Å) slightly longer than those along the bilayer (1.8862 Å). The interlayer distances, deÞ ned as the distances along [0001] between Si-Si layers, which may occur either in cubic (c) or hexagonal (h) conÞ gurations, are maximal at the c-h interface (2.5270 Å) and minimal at the h-c interface (2.5165 Å), entailing that the h-bilayer is not equidistant from either c-bilayers. All the tetrahedral angles are identical within the experimental error and close to the ideal value of 109.47°, but those at the c-h interface, where a signiÞ cant distortion of 0.15° is recorded. Finally, the anisotropic displacement factors are utterly very small, identical among different atoms within the experimental error, and signiÞ cantly spherical. It thus appears that the 6H-SiC structure is affected by a slight relaxation along the [0001] stacking direction with respect to the ideal cubic structure, and that the relaxation is mainly accomplished at the c-h interface, i.e., at the twin-like boundary, where a bilayer in cubic conÞ guration links a bilayer in antiparallel, hexagonal conÞ guration. As far as we know this is the Þ rst crystal structure reÞ nement of a natural 6H-SiC moissanite. Possible implications on the polytype stability in the light of these results are brieß y discussed.

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“…This isotope fractionation corresponds to a formation temperature of 1,250°C ± 150°C, which is within a typical range for the formation of subcontinental lithospheric diamonds (1,150°C ± 100°C). The δ 13 C values of terrestrial SiC have also been reported to range from −18‰ to −35‰, which are much lower than coexisting diamond or CaCO 3 (37,38). Thus, the observed low δ With increasing depth within the mantle, CO 2 and carbonates become unstable with respect to diamond at 120-200 km.…”

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confidence: 95%

Carbon-bearing iron phases and the carbon isotope composition of the deep Earth

Juske

Polyakov

2014

Proc. Natl. Acad. Sci. U.S.A.

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The carbon budget and dynamics of the Earth’s interior, including the core, are currently very poorly understood. Diamond-bearing, mantle-derived rocks show a very well defined peak at δ13C ≈ −5 ± 3‰ with a very broad distribution to lower values (∼−40‰). The processes that have produced the wide δ13C distributions to the observed low δ13C values in the deep Earth have been extensively debated, but few viable models have been proposed. Here, we present a model for understanding carbon isotope distributions within the deep Earth, involving Fe−C phases (Fe carbides and C dissolved in Fe−Ni metal). Our theoretical calculations show that Fe and Si carbides can be significantly depleted in 13C relative to other C-bearing materials even at mantle temperatures. Thus, the redox freezing and melting cycles of lithosphere via subduction upwelling in the deep Earth that involve the Fe−C phases can readily produce diamond with the observed low δ13C values. The sharp contrast in the δ13C distributions of peridotitic and eclogitic diamonds may reflect differences in their carbon cycles, controlled by the evolution of geodynamical processes around 2.5–3 Ga. Our model also predicts that the core contains C with low δ13C values and that an average δ13C value of the bulk Earth could be much lower than ∼−5‰, consistent with those of chondrites and other planetary body. The heterogeneous and depleted δ13C values of the deep Earth have implications, not only for its accretion−differentiation history but also for carbon isotope biosignatures for early life on the Earth.

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Natural occurrence of silicon carbide in a diamondiferous kimberlite from Fuxian

Cited by 71 publications

References 9 publications

Many Chemistries Could Be Used to Build Living Systems

Many Chemistries Could Be Used to Build Living Systems

The 6H-SiC structure model: Further refinement from SCXRD data from a terrestrial moissanite

Carbon-bearing iron phases and the carbon isotope composition of the deep Earth

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