Abstract

Several mechanisms and intermediate steps have been proposed to explain the transformation of graphite to diamond. However, the mechanism continues to be debated, in part because graphite that is incompletely transformed to diamond has not been reported; although such material could be used to better understand the diamond-forming process. Here we report the discovery of nano-sized grains of interstratified graphite and diamond from Gujba, an extraterrestrially shocked meteorite. We use high-resolution transmission electron microscopy (HRTEM) data from these grains to show that diamond formed via a reconstructive, topotactic rather than martensitic mechanism. Electron diffraction and HRTEM images show the following three-dimensional crystallographic relationships between the interstratified graphite and diamond: (001)g||(111) d, (100)g||(211)d, and (120) g||(011)d. These relationships yield the transition matrix linking the graphite and diamond unit cells, which become coincident for graphite compressed to 7 GPa. The specific product, whether single-crystal or twinned diamond, is dictated by the initial graphite polytype and transformation route. The derivation of a three-dimensional transition matrix is consistent with a topotactic relationship between graphite and the newly formed diamond.

Original languageEnglish (US)
Pages (from-to)531-538
Number of pages8
JournalAmerican Mineralogist
Volume99
Issue number2-3
DOIs
StatePublished - Feb 2014

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Diamond
Graphite
graphite
diamond
diamonds
High resolution transmission electron microscopy
transmission electron microscopy
Meteorites
matrix
high resolution
meteorites
Electron diffraction
meteorite
diffraction
derivation
electron diffraction
routes
Single crystals
crystal
electron

Keywords

  • crystal growth
  • Crystal structure
  • electron microscopy
  • meteorite

ASJC Scopus subject areas

  • Geochemistry and Petrology
  • Geophysics

Cite this

Transformation of graphite to diamond via a topotactic mechanism. / Garvie, Laurence; Németh, Péter; Buseck, P R.

In: American Mineralogist, Vol. 99, No. 2-3, 02.2014, p. 531-538.

Research output: Contribution to journalArticle

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