title: The nature and origin of interstellar diamond.
abstract: Microscopic diamond was recently discovered in oxidized acid residues from several carbonaceous chondrite meteorites (for example, the C delta component of the Allende meteorite).  Some of the reported properties of C delta seem in conflict with those expected of diamond.  Here we present high spatial resolution analytical data which may help to explain such results.  The C delta diamond is an extremely fine-grained (0.5-10 nm) single-phase material, but surface and interfacial carbon atoms, which may comprise as much as 25% of the total, impart an 'amorphous' character to some spectral data.  These data support the proposed high-pressure conversion of amorphous carbon and graphite into diamonds due to grain-grain collisions in the interstellar medium although a low-pressure mechanism of formation cannot be ruled out.
authors.affiliation: NASA Ames Research Center, Moffett Field, California 94035, USA.
authors.forename: D F
authors.initials: DF
authors.lastname: Blake
authors.forename: F
authors.initials: F
authors.lastname: Freund
authors.forename: K F
authors.initials: KF
authors.lastname: Krishnan
authors.forename: C J
authors.initials: CJ
authors.lastname: Echer
authors.forename: R
authors.initials: R
authors.lastname: Shipp
authors.forename: T E
authors.initials: TE
authors.lastname: Bunch
authors.forename: A G
authors.initials: AG
authors.lastname: Tielens
authors.forename: R J
authors.initials: RJ
authors.lastname: Lipari
authors.forename: C J
authors.initials: CJ
authors.lastname: Hetherington
authors.forename: S
authors.initials: S
authors.lastname: Chang
mesh_terms: D002244:Carbon / Q000737:chemistry*; D018130:Diamond / Q000032:analysis*; D019418:Evolution, Chemical; D018559:Exobiology; D005118:Extraterrestrial Environment; D019110:Meteoroids; D008855:Microscopy, Electron, Scanning; D016082:Solar System
chemical_list: D002244:Carbon; D018130:Diamond