Lonsdaleite is a hexagonal allotrope of the carbon allotrope diamond, believed to form when meteoric graphite falls to Earth. The great heat and stress of the impact transforms the graphite into diamond, but retains graphite's hexagonal crystal lattice. Lonsdaleite was first identified from the Canyon Diablo meteorite at Barringer Crater (also known as Meteor Crater) in Arizona. It was first discovered in 1967. 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 the Tunguska impact site, Russia. A regular hexagon A hexagon (also known as sexagon) is a polygon with six edges and six vertices. ... Eight allotropes of carbon: diamond, graphite, lonsdaelite, C60, C540, C70, amorphous carbon and a carbon nanotube. ... For other uses, see Diamond (disambiguation). ... Photo of a burst of meteors with extended exposure time A meteor is the visible path of a meteoroid that enters the Earths (or another bodys) atmosphere, commonly called a shooting star or falling star. ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... Earth is the current Good Article Collaboration of the week! Please help to improve this article to the highest of standards. ... It has been suggested that crystallization processes be merged into this article or section. ... In mineralogy and crystallography, a crystal structure is a unique arrangement of atoms in a crystal. ... The Canyon Diablo meteorite impacted at Barringer Crater, Arizona and is known from fragments collected around the crater and nearby Canyon Diablo which lies about 3 to 4 miles west of the crater. ... The Barringer Crater, also known as the Meteor Crater, is a famous impact crater created by a meteorite, located about 55 kilometers east of Flagstaff in the northern Arizona desert (USA). ... Official language(s) None Capital Largest city Phoenix Phoenix Area  Ranked 6th  - Total 113,998 sq mi  (295,254 km²)  - Width 310 miles (500 km)  - Length 400 miles (645 km)  - % water 0. ... 1967 (MCMLXVII) was a common year starting on Sunday of the Gregorian calendar (the link is to a full 1967 calendar). ... Official language(s) None; English and Spanish de facto Capital Largest city Santa Fe Albuquerque Area  Ranked 5th  - Total 121,665 sq mi  (315,194 km²)  - Width 342 miles (550 km)  - Length 370 miles (595 km)  - % water 0. ... right Artists rendition of the Tunguska Event Tunguska (Тунгуска) is a remote, largely uninhabited region in Siberia, Russia. ...

Lonsdaleite is also known as "hexagonal diamond." It is transparent brownish-yellow in color and has an index of refraction from 2.40 to 2.41, a specific 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. The refractive index of a material is the factor by which the phase velocity of electromagnetic radiation is slowed relative to vacuum. ... Relative density (also known as specific gravity) is a measure of the density of a material. ... Mohs scale of mineral hardness characterizes the scratch resistance of various minerals through the ability of a harder material to scratch a softer. ... Poly(hydridocarbyne) (PHC) is one of a class of carbon-based random network polymers primarily composed of tetrahedrally hybridized carbon atoms, each having one hydride substituent, exhibiting the generic formula [HC]n. ...

Lonsdaleite was named in honour of Kathleen Lonsdale. Dame Kathleen Lonsdale (January 28, 1903 - April 1, 1971) was a prominent crystallographer, who discovered the planar hexagonal structure of benzene. ...

Lattice Structure

Six-atom carbon rings in diamond uniformly take on the chair conformation of cyclohexane (marked 1) above. While most six-atom rings in lonsdaleite take on the same chair-conformation, others form the boat-conformation (marked 4), thus distinguishing its lattice structure from that of diamond.

Other allotropes of carbon can be described easily by referencing the base units of their lattice e.g. graphite is a flat sheet of benzene rings, where each ring consists only of carbon atoms bonded to other carbon atoms through double bonds with angles of 120 degrees between all bonds. However, the difference between lonsdaleite and diamond cannot be explained quite so simply. Image File history File links Cyclohexane_universe. ... Image File history File links Cyclohexane_universe. ... Graphite (named by Abraham Gottlob Werner in 1789, from the Greek γραφειν: to draw/write, for its use in pencils) is one of the allotropes of carbon. ... Benzene, also known as C6H6, PhH, and benzol, is an organic chemical compound that is a colorless and flammable liquid with a pleasant, sweet smell. ... Covalent bonding is a form of chemical bonding characterized by the sharing of one or more pairs of electrons between atoms, in order to produce a mutual attraction, which holds the resultant molecule together. ...

One common misconception is that lonsdaleite consists of a structure comprised of only of identical cyclohexane rings. However, this is only really true of pure diamond: every six carbon atom ring that can be found in the lattice of diamond is shaped identically to that of the most stable cyclohexane ring conformation. Such rings are characterized by their six single bonds, with angles of 109.5 degrees between each bond, and are not flat but instead form a chair structure (see diagram) in which any two carbon atoms opposite each other on the ring (those in positions 1 and 4, 2 and 5, and 3 and 6) take up spatial locations that are as far apart as possible. The structure of diamond is the most stable in existence for carbon, and is responsible for diamond's extreme hardness. Cyclohexane is a molecule with the molecular formula C6H12 (molar mass = 84. ... For other uses, see Diamond (disambiguation). ... Covalently bonded hydrogen and carbon in a molecule of methane. ... Cyclohexane conformation is a much studied topic in organic chemistry because of the complex interrelationship between the different conformers of cyclohexane and its derivatives. ...

The structure of lonsdaleite is very similar to that of diamond in that all six member rings in the lattice contain carbon atoms linked only by single bonds with 109.5 degrees between each bond. The difference is that not all such rings in lonsdaleite take the form of the chair structure; some rings form what is called a boat structure leaving the unbonded distance between adjacent carbon atoms smaller than that of the chair structure. This is fundamentally less stable, and causes the hardness of lonsdaleite to be slightly less than that of diamond. Despite the fact that the presence of boat-structure-rings in lonsdaleite is the mineral's defining characteristic, most rings in its lattice still form the more stable chair conformation. Cyclohexane conformation is a much studied topic in organic chemistry because of the complex interrelationship between the different conformers of cyclohexane and its derivatives. ...

A diagram of the structure of lonsdaleite can be viewed here: [1]. A diagram of the structure of diamond can be viewed here: [2].

References

• Mindat.org accessed 3/13/05.
• Webmineral accessed 3/13/05.
• Anthony, J.W.; et al (1995). Mineralogy of Arizona, 3rd.ed..
• Frondel, C., U.B. Marvin (1967). "Lonsdaleite, a new hexagonal polymorph of diamond". Nature 214: 587–589.
• Frondel, C., U.B. Marvin (1967). "Lonsdaleite, a hexagonal polymorph of diamond". Am.Min. 52.
• Bianconi, P., et al (2004). "Diamond and Diamond-like Carbon from a Preceramic Polymer". J. Am. Chem. Soc. Vol. 126 (10): 3191–3202.
• Materials Science and Technology Division, Naval Research Laboratory website accessed 5/14/2006.