- Lonsdaleite
Hexagonal diamond or commonly Lonsdaleite (named in honour of
Kathleen Lonsdale ) is anallotrope of carbon with a hexagonal lattice, believed to form whenmeteor icgraphite falls toEarth . The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonalcrystal lattice. Lonsdaleite was first identified from theCanyon Diablo meteorite atBarringer Crater (also known as Meteor Crater) inArizona . It was first discovered in1967 . Lonsdaleite occurs as microscopic crystals associated with diamond in the Canyon Diablo meteorite; Kenna meteorite,New Mexico ; and Allan Hills (ALH) 77283, Victoria Land,Antarctica meteorite. It has also been reported from theTunguska impact site ,Russia .It is transparent brownish-yellow in
color and has an index of refraction from 2.40 to 2.41, aspecific gravity from 3.2 to 3.3, and a Mohs hardness of 7–8. The Mohs hardness of diamond is 10; the lower hardness of lonsdaleite is chiefly attributed to impurities and imperfections in the naturally occurring material. It can also be created by the thermal decomposition of a polymer,poly (hydridocarbyne) , at atmospheric pressure under argon starting at 110 °C.Crystal Structure
Lonsdaleite has a hexagonal
unit cell , related to thediamond unit cell in the same way that the hexagonal and cubic close packedcrystal system s are related.The diamond structure can be considered to be made up of interlocking rings of six carbon atoms, in the
chair conformation . In Lonsdaleite some of the rings are in the boat conformation instead.A diagram of the structure of lonsdaleite can be viewed here: [http://cst-www.nrl.navy.mil/lattice/struk.picts/hexdia.s.png] .A diagram of the structure of diamond can be viewed here: [http://cst-www.nrl.navy.mil/lattice/struk.picts/a4.s.png] .
ee also
*
List of minerals
*List of minerals named after people References
* cite book
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coauthors = "et al"
year = 1995
title = Mineralogy of Arizona
edition = 3rd edition
* cite journal
last = Frondel | first = C.
coauthors = U.B. Marvin
year = 1967
title = Lonsdaleite, a new hexagonal polymorph of diamond
journal = Nature
volume = 214
pages = 587–589
doi = 10.1038/214587a0
* cite journal
last = Frondel | first = C.
coauthors = U.B. Marvin
year = 1967
title = Lonsdaleite, a hexagonal polymorph of diamond
journal = Am.Min.
volume = 52
* cite journal
last = Bianconi | first = P.
coauthors = "et al"
year = 2004
title = Diamond and Diamond-like Carbon from a Preceramic Polymer
journal = J. Am. Chem. Soc. Vol.
volume = 126
issue = 10
pages = 3191–3202
doi = 10.1021/ja039254lExternal links
* [http://www.mindat.org/min-2431.html Mindat.org] accessed 3/13/05.
* [http://webmineral.com/data/Lonsdaleite.shtml Webmineral] accessed 3/13/05.
* http://prola.aps.org/pdf/PRB/v67/i2/e024108
* [http://cst-www.nrl.navy.mil/lattice/struk/hexdia.html Materials Science and Technology Division, Naval Research Laboratory website] accessed 5/14/2006.
* [http://octettruss.kilu.de/diamond.html lonsdaleite 3D animation]
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