Hexagonal Diamonds in Meteorites: Implications

Abstract

A new polymorph of carbon, hexagonal diamond, has been discovered in the Canyon Diablo and Goalpara meteorites. This phase had been synthesized recently under specific high-pressure conditions in the laboratory. Our results: provide strong evidence that diamonds found in these meteorites were produced by intense shock pressures acting on crystalline graphite inclusions present within the meteorite before impact, rather than by disintegration of larger, statically grown diamonds, as some theories propose.

The martensitic transformation in silicon—III. comparison with other work

“…and Marvin [24] and by Hanneman et al [28]. The latter also observed dh diamond in Goalpara meteorites.…”

“…According to Hanneman et al [28]. their evidence indicates that cubic diamond cannot be transformed, even partially.…”

Lonsdaleite is faulted and twinned cubic diamond and does not exist as a discrete material

“…Diamond is reported to have a number of polytypes, of which lonsdaleite (also called hexagonal diamond) has received particularly intense attention. Lonsdaleite was first described almost 50 years ago from the Canyon Diablo iron meteorite 1,2 . Its formation was attributed to shock-induced transformation of graphite within the meteorite upon impact with Earth, and its occurrence was used as an indicator of shock [1][2][3] .…”

“…Lonsdaleite was first described almost 50 years ago from the Canyon Diablo iron meteorite 1,2 . Its formation was attributed to shock-induced transformation of graphite within the meteorite upon impact with Earth, and its occurrence was used as an indicator of shock [1][2][3] . It has since been reported from several meteorites as well as from terrestrial sediments and has been attributed to asteroidal impacts, both extraterrestrial and on Earth [4][5][6][7] .…”

Shock-compressed graphite to diamond transformation on nanosecond time scales

“…A good understanding of this particular transition is important for gaining insight into shockinduced phase transformations, 2 study of meteorite impacts, 3,4 technological applications involving the synthesis of industrial diamonds, 5,6 and for linking the shock work to static high pressure -high temperature (HP-HT) studies. 7 Although gem quality diamonds can now be fabricated routinely using chemical vapor deposition (CVD) approaches, 23,24 a detailed understanding of the shock-induced graphite to diamond transformation remains an important scientific challenge.…”