Experimental shock synthesis of diamonds in a graphite gneiss

Kenkmann, T.; Hornemann, U.; Stöffler, D.

doi:10.1111/j.1945-5100.2005.tb00402.x

Cited by 15 publications

(11 citation statements)

References 23 publications

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“…These processes were heating through void collapse (experiments GG092 and GG094)47, frictional heating due to mineral impedance contrasts (experiment GG093) and shock compression effects (experiments GG094 and GG095)48. The general experimental conditions are listed in Supplementary Table 1 and analytical results are detailed below.…”

Section: Resultsmentioning

confidence: 99%

Shock-transformation of whitlockite to merrillite and the implications for meteoritic phosphate

et al. 2017

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Meteorites represent the only samples available for study on Earth of a number of planetary bodies. The minerals within meteorites therefore hold the key to addressing numerous questions about our solar system. Of particular interest is the Ca-phosphate mineral merrillite, the anhydrous end-member of the merrillite–whitlockite solid solution series. For example, the anhydrous nature of merrillite in Martian meteorites has been interpreted as evidence of water-limited late-stage Martian melts. However, recent research on apatite in the same meteorites suggests higher water content in melts. One complication of using meteorites rather than direct samples is the shock compression all meteorites have experienced, which can alter meteorite mineralogy. Here we show whitlockite transformation into merrillite by shock-compression levels relevant to meteorites, including Martian meteorites. The results open the possibility that at least part of meteoritic merrillite may have originally been H+-bearing whitlockite with implications for interpreting meteorites and the need for future sample return.

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Section: Resultsmentioning

confidence: 99%

Shock-transformation of whitlockite to merrillite and the implications for meteoritic phosphate

et al. 2017

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“…The key difference between laboratory experiments and natural shock events during impact cratering relates to the enormous energy released during natural impacts, and long duration of a large natural shock pulse (~1 second) that may be many orders of magnitude longer than those (~ns-s) that can be replicated in the laboratory (De Carli et al, 2002;DeCarli et al, 2002) (Sharp and DeCarli, 2006). Additional processes related to mineralogical complexity may include the transient appearance of very hot (3000-4000K) impact melts (Kenkmann et al, 2005).…”

Section: Stable and Metastable Phase Relations: Diamond "Lonsdaleitementioning

confidence: 99%

Structural characterization of natural diamond shocked to 60 GPa; implications for Earth and planetary systems

Jones

McMillan

Salzmann

et al. 2016

Lithos

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The possible presence of the high-density carbon polymorph with hexagonal symmetry known as "lonsdaleite" provides an important marker for shock impact events. It is typically considered to form as a metastable phase produced from graphite or other carbonaceous precursors. However, its existence has recently been called into question. Here we collected high-resolution synchrotron X-ray diffraction data for laboratory-shocked and natural impact diamonds that both show evidence for deviations from cubic symmetry, that would be consistent with the appearance of hexagonal stacking sequences. These results show that hexagonality can be achieved by shocking diamond as well as from graphite precursors. The diffraction results are analyzed in terms of a general model that describes intermediate stacking sequences between pure diamond (fully cubic) and "lonsdaleite" (fully hexagonal) phases, with provision made for ordered vs disordered stacking arrangements. This approach provides a "hexagonality index" that can be used to characterize and distinguish among samples that have experienced different degrees of shock or static high pressure-high temperature treatments. We have also examined the relative energetics of diamond and "lonsdaleite" structures using density functional theoretical (DFT) methods. The results set limits on the conditions under which a transformation between diamond and "lonsdaleite" structures can be achieved. Calculated Raman spectra provide an indicator for the presence of

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“…Whereas complex organics are unstable at the higher temperatures experienced outside of Mercury's permanently shadowed regions, graphite and amorphous carbon, the most likely products from high-temperature impact vaporization and re-condensation, are thermally stable to up to 4,000 K, permitting global distribution. Nanodiamonds, well-known products of hypervelocity impacts into carbon 30 , should also accumulate through ongoing bombardment. Regardless of local or regional variations in reflectance, the globally distributed presence of an unidentified opaque material, which we propose to be carbon, is necessary to explain Mercury's low overall reflectance throughout all terrain types 1,12 .…”

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confidence: 99%

Darkening of Mercury's surface by cometary carbon

2015

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Mercury's surface is darker than that of the Moon 1,2 . Ironbearing minerals and submicroscopic metallic iron produced by space weathering are the primary known darkening materials on airless bodies. Yet Mercury's iron abundance at the surface is lower than the Moon's 3,4 ; another material is therefore likely to be responsible for Mercury's dark surface 1,2,5-8 . Enhanced darkening by submicroscopic metallic iron particles under intense space weathering at Mercury's surface 9-12 is insu cient to reconcile the planet's low reflectance with its low iron abundance 12 . Here we show that the delivery of cometary carbon by micrometeorites provides a mechanism to darken Mercury's surface without violating observational constraints on iron content. We calculate the micrometeorite flux at Mercury and numerically simulate the fraction of carbonaceous material retained by the planet following micrometeorite impacts. We estimate that 50 times as many carbon-rich micrometeorites per unit surface area are delivered to Mercury, compared with the Moon, resulting in approximately 3-6 wt% carbon at Mercury's surface (in graphite, amorphous, or nanodiamond form). Spectroscopic analysis of products of hypervelocity impact experiments demonstrates that the incorporation of carbon e ectively darkens and weakens spectral features, consistent with remote observations of Mercury 1,2,5-8,12 . Carbon delivery by micrometeorites provides an explanation for Mercury's globally low reflectance and may contribute to the darkening of planetary surfaces elsewhere.Efforts to characterize the composition of Mercury's surface over the past several decades revealed a planet described by dark and featureless visible to near-infrared reflectance spectra; multispectral data acquired by the MESSENGER spacecraft recently reconfirmed the absence of a 1-µm absorption feature at Mercury 1,2,5-8 . The

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Experimental shock synthesis of diamonds in a graphite gneiss

Cited by 15 publications

References 23 publications

Shock-transformation of whitlockite to merrillite and the implications for meteoritic phosphate

Shock-transformation of whitlockite to merrillite and the implications for meteoritic phosphate

Structural characterization of natural diamond shocked to 60 GPa; implications for Earth and planetary systems

Darkening of Mercury's surface by cometary carbon

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