Yakutite Nanodiamond is Impact Ejecta from the Popigai Crater

by Tommy on 10/04/2017

There is a bit more to report on the ongoing lonsdaleite saga. It’s not quite a war. Yet. But close.


Mineralogical and crystallographic features of polycrystalline yakutite diamond, Hiroaki Ohfuji, Motosuke Nakaya, Alexander P. Yelissevev, Valentin P. Afanasiev and Konstantin D. Litasov, Journal of Mineralogical and Petrological Sciences, 112, 46-51 (1 February 2017), doi:10.2465/jmps.160719g

This study revealed for the first time the microtexture and crystallographic features of natural polycrystalline diamond, yakutite found in placer deposits in the Siberian Platform, Russia. Yakutite consists of well–sintered nanocrystalline (5–50 nm) diamond and small amount of lonsdaleite showing distinct preferred orientations. Micro–focus X–ray and electron diffractions showed a coaxial relationship between lonsdaleite 100 and diamond 111, suggesting the martensitic formation of yakutite from crystalline graphite. These textural and crystallographic features are well comparable to those of the impact diamonds from the Popigai crater located in the central Siberia and strongly support the idea that yakutite is a product of long–distance outburst from the Popigai crater, which has been inferred merely from the geochemical signatures.

See also: http://link.springer.com/article/10.1134/S1063776117010125

Investigation on the formation of lonsdaleite from graphite, V. A. Greshnyakov and E. A. Belenkov, Journal of Experimental and Theoretical Physics, 124, 2, 265–274 (23 March 2017), DOI:10.1134/S1063776117010125

Structural stability and the possible pathways to experimental formation of lonsdaleite—a hexagonal 2H polytype of diamond—have been studied in the framework of the density functional theory (DFT). It is established that the structural transformation of orthorhombic Cmmm graphite to 2H polytype of diamond must take place at a pressure of 61 GPa, while the formation of lonsdaleite from hexagonal P6/mmm graphite must take place at 56 GPa. The minimum potential barrier height separating the 2H polytype state from graphite is only 0.003 eV/atom smaller than that for the cubic diamond. The high potential barrier is indicative of the possibility of stable existence of the hexagonal diamond under normal conditions. In this work, we have also analyzed the X-ray diffraction and electron-microscopic data available for nanodiamonds found in meteorite impact craters in search for the presence of hexagonal diamond. Results of this analysis showed that pure 3C and 2H polytypes are not contained in the carbon materials of impact origin, the structure of nanocrystals found representing diamonds with randomly packed layers. The term “lonsdaleite,” used to denote carbon materials found in meteorite impact craters and diamond crystals with 2H polytype structure, is rather ambiguous, since no pure hexagonal diamond has been identified in carbon phases found at meteorite fall sites.

So lonsdaleite lives! But only fleetingly in impact nanodiamonds.

Shear strain is still the key to making lonsdaleite.

Exploding missiles is not the best way.

It takes nuance and finesse.


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