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Article: Lonsdaleite


Lonsdaleite Properties and Structure

  • Allotrope of carbon with a hexagonal lattice
  • Translucent and brownish-yellow in color
  • Refractive index of 2.40-2.41
  • Specific gravity of 3.2-3.3
  • Hardness theoretically superior to cubic diamond
  • Hexagonal unit cell with interlocking rings of six carbon atoms
  • Some rings are in the boat conformation
  • Bonds between layers are in the eclipsed conformation
  • Predicted to be 58% harder than diamond on the 100 face
  • Natural specimens exhibit a range of hardness values

Formation of Lonsdaleite

  • Formed when graphite in meteorites undergoes immense heat and stress
  • Retains graphite's hexagonal crystal lattice
  • First identified in the Canyon Diablo meteorite
  • Microscopic crystals associated with ordinary diamond
  • Synthesized in the laboratory by compressing and heating graphite
  • Lonsdaleite is formed by shock compression of graphite.
  • Nanosecond formation of diamond and lonsdaleite has been observed in laboratory experiments.
  • Shock-compressed graphite can transform into hexagonal diamond in nanoseconds.
  • Polycrystalline aggregates of diamond with lonsdaleite have been found in Yakutian placers.
  • Evidence from central Mexico supports the Younger Dryas extraterrestrial impact hypothesis.

Occurrence of Lonsdaleite

  • Found in meteorites such as Canyon Diablo, Kenna, and Allan Hills 77283
  • Naturally occurring in non-bolide diamond placer deposits in the Sakha Republic
  • Claims of Lonsdaleite in sediments at Lake Cuitzeo are uncertain
  • Presence in local peat deposits linked to the Tunguska event
  • Disputed claims of Lonsdaleite in the Greenland ice sheet

Manufacture of Lonsdaleite

  • Produced by compressing and heating graphite in a static press or using explosives
  • Chemical vapor deposition can also produce Lonsdaleite
  • Thermal decomposition of poly(hydridocarbyne) can yield Lonsdaleite
  • Accidental discovery of room temperature Lonsdaleite production using a diamond anvil cell
  • Creation of large Lonsdaleite crystals with lasers, although they are destroyed shortly after
  • Lonsdaleite can be synthesized through chemical vapor deposition.
  • Hexagonal diamond formation has been observed from dissolved carbon in nickel.
  • Hexagonal diamond synthesis has been achieved on strained films.
  • Poly(hydridocarbyne) can be synthesized as a precursor to diamond and diamond-like ceramics.
  • Electrochemical polymerization can be used to form poly(hydridocarbyne) for diamond production.

Discovery, Identification, and Properties of Lonsdaleite

  • Lonsdaleite was first discovered in meteorites.
  • It was named after Dame Kathleen Lonsdale, an Irish crystallographer.
  • Confocal Raman spectroscopy can be used to observe the formation of hexagonal diamond.
  • Lonsdaleite has been identified in the Greenland ice sheet.
  • New evidence suggests that the Tunguska cosmic body was of meteoritic origin.
  • Lonsdaleite is a form of diamond with a hexagonal crystal structure.
  • It is considered to be harder than cubic diamond.
  • Lab-made hexagonal diamonds have been found to be stiffer than natural cubic diamonds.
  • Lonsdaleite has potential applications in high-pressure experiments and as an abrasive material.
  • The properties of lonsdaleite make it a valuable material for scientific research.

Lonsdaleite Data Sources

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