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