Under some conditions, carbon crystallizes as lonsdaleite, a hexagonal crystal lattice with all atoms covalently bonded and properties similar to those of diamond.
12.
A quantitative analysis of the X-ray diffraction data of lonsdaleite has shown that about equal amounts of hexagonal and cubic stacking sequences are present.
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Some typical diamonds contain inclusions of common polymorph, lonsdaleite, have been found as inclusions in carbonados, although such inclusions might be expected if carbonados formed by meteorite impact.
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On the other hand, recent shock experiments with in situ X-ray diffraction show strong evidence for creation of relatively pure lonsdaleite in dynamic high-pressure environments such as meteor impacts.
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The property of lonsdaleite as a discrete material has been questioned, since specimens under crystallographic inspection showed not a bulk hexagonal lattice, but instead cubic diamond dominated by structural defects that include hexagonal sequences.
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One group examined carbon-14 dates for charcoal particles that showed wildfires occurred well after the proposed impact date, and the glass-like carbon was produced by wildfires and no lonsdaleite was found.
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The wurtzite form of boron nitride ( w-BN; point group = C 6v; space group = P6 3 mc ) has the same structure as lonsdaleite, a rare hexagonal polymorph of carbon.
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:I thought lonsdaleite occurs naturally and could in principle be harder than diamond ( except natural samples are never pure enough for that ) . talk ) 09 : 22, 8 May 2014 ( UTC)
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I would try to be clear about structures and show how lonsdaleite can be seen as derived from the diamond structure ( but hexagonal ) and nanotubes can be seen as derived from the graphite stucture ( rolled sheet ).
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I went to look this up, and according to Wikipedia, there's a whole nother kind of carbon called Lonsdaleite with a hexagonal matrix, which is harder than diamond in one plane but much softer in practice.
